Question 1

Does velocity banking, the HELOC chunking strategy, actually work?

Accepted Answer

Partly, and not for the reason it is sold on. Take the two halves separately. The chunking half moves balance from the mortgage to the line, and the interest avoided on one side and charged on the other follow the same amount over the same falling profile. They cancel except for the gap between the rates, so a 9% line against a 6.5% mortgage loses money on every cycle. Set the line to the mortgage rate on the velocity page and that figure goes to zero, to the cent.

The half that does work is the float. Income sitting against the line between payday and spending lowers the balance interest is charged on. That is worth your average float times the line rate, it has nothing to do with the lump sums, and you would get it without them. It is the same mechanism as an offset mortgage.

On the baseline loan with a 9% line, $9,000 of monthly income and a $10,000 chunk, ten years of it ends about $2,700 ahead of simply paying the same surplus into the mortgage, and about $48,000 ahead of paying only the minimum. The second number is the one you are shown, and roughly 94% of it is just paying extra.

Question 2

What is the catch with using a line of credit against my mortgage?

Accepted Answer

A fixed-rate mortgage cannot reprice, cannot be called and cannot be frozen. A home equity line can do all three, and it is secured by the same house. Moving balance from the first to the second changes what a bad year does to you, and that change appears in no total on any page here.

The costs the model leaves out all point the same way: setup and appraisal fees, annual fees, the draw period ending and becoming a repayment period, and a variable rate that moves in jumps rather than the smooth drift simulated here. Treat the figures as the friendly end of the range.

Question 3

Why does a $300,000 loan at 6.5% over 30 years cost about $682,637?

Accepted Answer

Because you make 360 payments of about $1,896.20, and 360 times $1,896.20 is $682,632. The level payment is rounded to the nearest cent, so the schedule underpays by a fraction of a cent each month and the final payment absorbs the residue, coming to $1,900.91 instead. The total is $682,637, of which $300,000 is the money you borrowed and $382,637 is interest.

The reason the interest is larger than the loan is that the balance stays large for a long time. Interest is charged every month on what you still owe, and on this loan you still owe about $189,000 after eighteen years. Roughly $1.28 of interest accompanies every dollar borrowed.

Nothing unusual is happening at 6.5%. The same loan at 3% costs $455,333 in total, and at 9% it costs $868,990. Time and balance do the work, not an unusual rate.

Question 4

Why is my first payment almost entirely interest?

Accepted Answer

Because interest is charged on the balance you currently owe, and at the first payment you owe the entire loan. One month of 6.5% on $300,000 is $1,625.00. Your payment is $1,896.20, so $1,625.00 goes to interest and $271.20 goes to principal, which is 14% of the payment.

From there it improves by itself. Each dollar of principal paid lowers the balance, which lowers next month interest charge, which leaves more of the same payment for principal. The split crosses fifty-fifty in month 233 on this loan.

This is not a fee structure or a trick in the paperwork. Any loan that charges interest on the outstanding balance and takes a level payment behaves this way.

Question 5

Why is an extra payment early worth so much more than the same amount later?

Accepted Answer

An extra dollar of principal removes the interest that dollar would have accrued over every month that remains. Early in the loan there are hundreds of months left, so the dollar works for a long time. Late in the loan there are few, so it works briefly.

On the baseline loan, $10,000 of extra principal in the first month removes about $53,600 of interest and pulls the payoff forward by 33 payments. The same $10,000 in year 25 removes about $4,400. That is roughly twelve times the effect for the same money, and the only difference is when it arrived.

This cuts both ways. It is the strongest argument for prepaying early, and also the reason cash committed early cannot be doing anything else for the same long stretch, which is exactly what the prepay versus invest comparison measures.

Question 6

How much does one extra payment a year actually save?

Accepted Answer

On the baseline loan, adding one twelfth of the payment to each month, which is $158.02, retires the loan in 290 payments instead of 360. That is about five years and eleven months earlier, and it lowers total interest from $382,637 to about $295,378, a saving of roughly $87,000.

Making one full extra payment once a year instead, in the twelfth month, gets you to 292 payments and saves about $84,000. The small difference is timing: the monthly version puts money to work sooner.

This is also what an accelerated biweekly plan does. Paying $948.10 every two weeks is 26 half payments, which equals 13 monthly payments a year. If a service charges a setup fee for that, it is charging you for an extra payment you can schedule yourself.

Question 7

Should I pay down the mortgage or invest the money?

Accepted Answer

The tool will not answer that for you, but it will make the tradeoff explicit. Prepaying earns a certain return exactly equal to your loan rate, because every dollar of principal removes interest that would definitely have been charged. Investing earns an uncertain return that you supply as an assumption.

The comparison is therefore between a known 6.5% and a number you typed. If the assumed after fee, after tax return is above the loan rate, the invest path ends with more money in the model, and if it is below, the prepay path does. The crossing point is visible on the prepay versus invest page.

Two things the arithmetic does not capture. Prepaid principal cannot be withdrawn without a sale or a new loan, so it costs liquidity, and an assumed return is not a realized one: the model has no volatility, so the invest path never has a bad decade.

Question 8

What does break-even mean for a refinance, and why does this tool show two of them?

Accepted Answer

The naive break-even divides the closing costs by the monthly payment saving. Six thousand dollars of costs against a $389 saving breaks even in 15 months. It answers one question: how long until the lower payment has repaid the fees.

The complete break-even compares the two whole positions month by month: everything paid so far on each path plus the balance still owed on each path. The first month where the refinanced position is the smaller number is the real break-even.

They differ whenever the new loan restarts the term. The naive figure cannot see that a lower payment may be lower because the debt was stretched, not because the rate fell. When the two disagree, the complete one is the one that accounts for what you still owe.

Question 9

How can a refinance with a lower monthly payment still cost me more?

Accepted Answer

Take the baseline loan five years in, with $280,833 left and 25 years to run. Refinancing into a new 30 year loan at 6.0% with $6,000 of costs drops the payment from $1,896.20 to $1,683.74. The naive break-even is 28 months, which sounds comfortable.

Over the life of that new loan you would pay about $606,144 plus the $6,000 in costs. Staying on the old loan costs about $568,865 from that same point. The refinance is roughly $43,000 more expensive even though every monthly payment is smaller.

The payment fell because 25 years of debt was respread over 30 years, and the half point of rate was not enough to offset the extra five years of interest. A lower payment is a cash flow fact, not a cost fact.

Question 10

Avalanche or snowball, and why do they give different answers?

Accepted Answer

Both pay every minimum and pour the leftover cash into one target debt. They differ only in which debt is the target: avalanche picks the highest rate, snowball picks the smallest balance. When those are the same debt, the two plans are identical.

Avalanche pays less total interest, because interest accrues per dollar at each rate and attacking the highest rate removes the most future interest. Snowball closes accounts sooner, which frees minimum payments earlier and shortens the list of bills you are managing.

Under a fixed budget the gap in dollars is usually modest, and the tool shows it for your actual debts rather than in the abstract. The comparison is between a measured amount of interest and a benefit you have to price yourself, which is why no ordering is labeled the winner here.

Question 11

Is my equity profit?

Accepted Answer

No. Equity has two sources and only one of them creates wealth. When you pay $500 of principal, your cash falls by $500 and your equity rises by $500. Your net worth at that instant has not moved at all: money changed form, from an account you can spend to an asset you cannot spend a piece of.

The other source is appreciation, and that one is new. Nothing left your pocket when the market revalued the house, so a $20,000 rise in value is a $20,000 rise in net worth, on paper.

Even the appreciation part is gross rather than net. Turning equity into money means selling, which costs 6% to 10% of the price, or borrowing against it, which creates a new debt. An equity chart that climbs steadily in a flat market is showing you cash conversion, not profit.

Question 12

My house doubled in 30 years. Is that a good return?

Accepted Answer

Doubling over 30 years is growth of 2.34% a year, because 2 raised to the power of one thirtieth is 1.0234. The word doubling sounds impressive because it hides the time it took.

If inflation averaged 2.5% over the same period, that doubling lost purchasing power. The nominal number went up and the real one did not, which is the most common way housing returns get overstated in conversation.

What the headline also omits is everything spent along the way: interest, taxes, insurance, maintenance and the cost of the sale itself. The equity page reports appreciation as a compound annual rate for exactly this reason.

Question 13

What happens to the numbers if my house does not appreciate at all?

Accepted Answer

Set appreciation to zero and the value line goes flat. Equity still rises, but only from principal paid, so the equity curve becomes a record of cash you moved rather than of wealth created.

The sale side changes more sharply. Selling costs are charged on the price regardless of any gain, so a sale in the early years returns less than you put in: the down payment, the closing costs and every dollar of interest and escrow are gone, and the only thing coming back is the principal you paid minus the cost of selling.

This is worth running before any decision that assumes appreciation. If a plan only works at 4% a year, the plan is a bet on the housing market, and the zero case tells you how large the bet is.

Question 14

What if the house falls 20% in value?

Accepted Answer

The loan balance does not move with the market, so the entire fall lands on your equity. On a $400,000 home, a 20% fall removes $80,000 of equity whether your equity was $200,000 or $40,000.

With 20% down, that fall takes essentially all of your equity: you owe about $320,000 on a home now worth $320,000, and after selling costs a sale would not cover the loan. With 10% down you would be underwater, meaning you would need to bring cash to closing in order to sell.

This is the downside face of leverage, and the model shows it exactly: enter a negative appreciation rate, or use the sensitivity page to sweep appreciation across a range and watch where net proceeds cross zero.

Question 15

Why does the tool refuse to tell me which option is best?

Accepted Answer

Because best requires weights that only you hold. Paying off a loan faster, keeping cash liquid, lowering the monthly payment and maximizing expected ending wealth are four different objectives, and no arithmetic converts one into another without a preference about your life.

What the tool can do without guessing is remove the options that lose on every objective at once. That step needs no weights, and what remains is the Pareto frontier, where each option gives up something to gain something.

So the optimizer returns a frontier and a handful of representative configurations rather than a single score. The comparison is honest; the choice is yours.

Question 16

How does leverage amplify gains and losses?

Accepted Answer

With 20% down you control five dollars of house for every dollar of your own money. Because the loan is a fixed claim, every dollar the house gains or loses lands on your equity, so a 5% rise in value is a 25% rise in your stake and a 5% fall is a 25% fall.

The amplification is symmetric, but the cost of holding it is not. Interest accrues every month whether the house rose, fell or did nothing, so the break-even move is not zero, it is whatever the carrying cost amounts to.

This is why return on the asset and return on your equity are two different numbers, and why the equity page reports both. One describes the property, the other describes your outcome.

Question 17

What does IRR mean for a home I live in, and why is it easy to misread?

Accepted Answer

IRR is the single annual rate that makes the present value of all the cash flows equal to zero. For a home the flows are the down payment and closing costs going out, every housing payment going out, and the net proceeds coming in at the sale.

Read literally, that series is all negative until the end, so the rate it produces describes the home as an asset that paid nothing for years. That understates it, because you were housed the whole time, which is why the tool also reports the return with imputed rent counted as a benefit.

Three more traps. A series whose signs alternate more than once can have several mathematically valid rates, a series that never turns positive has none, and IRR says nothing about the size of the result: a spectacular rate on a tiny amount of capital is a small amount of money. When the series is ambiguous the tool reports no rate rather than a confident one.

Question 18

Why compute a return both with and without imputed rent?

Accepted Answer

Because a home is two things at once: an asset you own and a service you consume. Counting only the cash flows prices the asset. Counting the rent you did not have to pay prices the whole arrangement, including the living in it.

The two numbers usually disagree by a lot. Without imputed rent, a home held for seven years often shows a poor return or a negative one after transaction costs. With it, the same period can look reasonable, because the monthly benefit was real even though no money arrived.

Neither figure is the true one. The version without rent is comparable to a stock portfolio, the version with rent is comparable to renting the same house, and knowing which question you are asking is the point of showing both.

Question 19

What does this tool deliberately not model?

Accepted Answer

Volatility above all. Every projection is deterministic, so the invest path never has a bad decade and the house never has a bad year unless you enter one. Returns compound smoothly at whatever rate you typed.

Also excluded: taxes beyond a single flat rate applied to investment gains and an optional mortgage interest deduction, inflation unless you switch it on, job loss or any interruption of income, rate resets on adjustable loans, prepayment penalties, loan recasting, private mortgage insurance rules that vary by program, association special assessments, and the state and local variation in nearly every cost line.

The reason is not laziness. Each of those needs an assumption that is far less knowable than a rate or a term, and a model that quietly invents one produces confident output from invented inputs. Where a number rests on an assumption, the page showing it says so.

Question 20

Why is there no Monte Carlo simulation?

Accepted Answer

A Monte Carlo run needs a volatility, a distribution shape and correlations between house prices, market returns and interest rates. Those inputs are much harder to know than a rate or a term, and a wrong distribution produces confident percentile bands anyway.

There is also a presentation problem. A fan chart reads as a forecast, and people take the median of a simulation as a prediction of their own life.

The alternative offered here is deterministic and inspectable: change one input on purpose and see exactly what it does. The sensitivity page sweeps a single variable across a range, and the scenario page holds several complete alternatives side by side.

Question 21

Where is my data stored, and does anything leave my browser?

Accepted Answer

None of your numbers leave your browser. There is no backend and no account, and every calculation on every page runs locally in this tab, including the optimizer, which runs in a web worker to keep the interface responsive. The site does count page views so I can see which tools get used, but that report carries the name of the page and nothing else: no cookie, no identifier that follows you between visits, and nothing drawn from a scenario.

Your scenarios, debts and preferences are saved in this browser local storage under a single versioned key. That is why they survive a reload and why they do not follow you to another device or another browser.

Clearing site data removes them permanently. If the numbers matter to you, export a backup from the settings page.

Question 22

How do I export and import my data?

Accepted Answer

The settings page has two export buttons. One writes a full backup as JSON, containing every scenario, your debts and your preferences. The other writes the active scenario alone, which is the file to share when someone wants to reproduce one specific setup.

Import accepts either shape. A full backup replaces everything currently in the browser, and a single scenario is added to your list without disturbing what is already there. If the file is valid JSON but not recognizable, nothing is changed and the page says so.

The amortization table also exports to CSV, which is the format to use when you want to check the arithmetic in a spreadsheet.

Question 23

Why is the last payment different from all the others?

Accepted Answer

The level payment is rounded to whole cents, so it almost never divides the loan perfectly. Over hundreds of months those fractions of a cent accumulate into a small residue, and the final payment is trimmed or extended so the balance lands on exactly zero.

On the baseline loan there are 360 payments: 359 of $1,896.20 and a final one of $1,900.91, which carries the accumulated rounding residue. Your lender does the same thing, which is why a real payoff statement rarely matches the regular payment.

Any extra principal makes this more visible, since the final scheduled payment is then whatever is left of the balance plus one month of interest on it.

Question 24

How does the tool handle rounding?

Accepted Answer

Every amount is an integer number of cents, so sums, differences and running balances are exact and no fractional dollar is ever stored. That is the only way a schedule of several hundred rows still reconciles with its totals at the end.

Whenever a rate multiplies a balance, or a factor is raised to a power, the calculation goes through a decimal library and is rounded once to a whole cent, half up, which is the convention lenders use. Rounding happens at that single point and never again downstream.

Display formatting is separate and never feeds back into the engine. A chart axis reading $1.2M is a label; the number behind it is still exact to the cent.

Question 25

Is PMI included in the interest figures?

Accepted Answer

No. PMI is insurance that protects the lender against default. It does not accrue on your balance and it stops when the loan to value threshold is reached even though the loan continues, so folding it into interest would misstate both numbers.

The tool tracks it inside the monthly housing payment, alongside property tax, insurance and association dues, and reports it as its own line. The same applies to escrow items: they are part of what you pay each month and none of them are part of the cost of borrowing.

This also means prepaying does not reduce them. What extra principal can do is reach the cancellation threshold sooner, which ends PMI earlier.

Question 26

Does this tool give financial advice?

Accepted Answer

No. It provides mathematical simulations for educational and planning purposes, and it does not provide financial, tax, legal or investment advice. It has no view on what you should do.

Every output is arithmetic performed on inputs you supplied. Change an assumption and the conclusion can reverse, which is a feature of the model and a reminder about how much the conclusion depends on the assumption.

Actual loan terms, taxes, investment returns, insurance costs and lender calculations may differ from what is shown here. A decision of this size is worth checking against the actual documents and, where the stakes justify it, with a professional who can see your whole situation.

Question 27

What does amortization actually mean?

Accepted Answer

It is the process of retiring a loan with a series of payments, where each payment covers the interest accrued since the last one and applies whatever is left to the balance.

The payment stays level while its composition shifts. Interest is charged on what is outstanding, so as the balance falls the interest portion falls and the principal portion grows to fill the same payment.

The amortization schedule is the row by row record of that process, and it is the ground truth for this app. Totals such as lifetime interest and payoff date are sums over that table rather than separate formulas, which is why they always agree with each other.

Question 28

What is the difference between the interest rate and the APR?

Accepted Answer

The interest rate determines your payment. The APR folds certain loan fees into a single annualized number so that two offers with different fee structures can be compared on one figure.

The catch is that APR spreads those fees over the full term. If you sell or refinance in year five, fees that the APR amortized over 30 years were actually consumed in five, so the APR understates their cost. Lenders also differ in which fees they include.

For a decision about your own holding period, comparing the total cash out of pocket over that period is more informative than comparing two APRs.

Question 29

Why does 6.5% not cost exactly 6.5% a year?

Accepted Answer

Because a mortgage quoted at 6.5% charges one twelfth of it each month, and those twelve charges compound. The effective annual rate is 6.697%.

The quoted rate is a convention for dividing, not a statement about what a year costs. Products with different compounding conventions can quote the same nominal rate and cost different amounts.

The tool follows the US mortgage convention throughout: the periodic rate is the annual rate divided by the number of payments per year, applied to the balance at the start of each period.

Question 30

Should I take a 15 year loan instead of a 30 year one?

Accepted Answer

The tool will show you the tradeoff rather than pick. A shorter term raises the payment and cuts lifetime interest sharply, because the balance falls faster and interest is charged on what remains.

The mirror image is flexibility. A 30 year loan with voluntary extra principal can reach a similar payoff date while leaving you free to stop paying extra in a bad month. A 15 year loan commits you contractually, which is often priced with a lower rate for exactly that reason.

Build both as scenarios and compare them on the metrics you care about: payment, total interest, payoff date and the cash left over each month. The scenario page holds them side by side.

Question 31

Do biweekly payments really save money?

Accepted Answer

It depends which plan you mean. Splitting your 12 monthly payments into 24 half payments is a cash flow convenience tied to paychecks and saves a negligible amount.

Paying every two weeks is different: a year holds 26 two week periods, so 26 half payments add up to 13 monthly payments. That thirteenth payment is the entire source of the savings, and on the baseline loan it retires the loan in about 24 years instead of just over 30.

The same result comes from adding one twelfth to each monthly payment yourself. A service charging a setup fee to arrange it is charging for scheduling, not for arithmetic.

Question 32

Will extra principal lower my monthly payment?

Accepted Answer

No, not by itself. Extra principal shrinks the balance, which means every remaining interest charge is computed on a smaller number and the schedule runs out of months earlier. The payment amount is unchanged.

What lowers the payment is recasting, where the servicer recomputes the payment from the reduced balance over the remaining term, usually for a fee and a minimum prepayment. Not every loan offers it and this tool does not model it.

This matters for cash flow planning. Prepaying improves your position but does not help the month your income drops, which is the argument for keeping a reserve separate from the loan.

Question 33

I have a lump sum. Does it matter which month I apply it?

Accepted Answer

Yes, and by more than most people expect. A lump sum removes the interest it would have accrued over the months that remain, so the earlier it lands the longer it works.

On the baseline loan, $10,000 applied in month 1 removes about $53,600 of interest. The same amount in month 61 removes about $37,100, and in month 241 about $8,600. Nothing about the loan changed, only the timing.

The extra payments editor lets you place a one time amount in any month, and the comparison panel reports the interest and months saved against the same loan without it.

Question 34

Could I be penalized for paying early?

Accepted Answer

Some loans carry a prepayment penalty, usually a percentage of the amount prepaid or a set number of months of interest, and typically limited to the first few years. Many mortgages have none, and several loan programs are barred from carrying one.

This tool does not model penalties. If your note has one, the interest saved shown here is larger than what you would actually keep, and the same applies to any refinance, which triggers the penalty as well.

The place to check is the note itself rather than the marketing sheet, since the term appears in the loan documents.

Question 35

How do I tell whether a refinance is worth it?

Accepted Answer

Enter the offer and read the complete break-even, then compare it with how long you expect to hold the loan. A break-even beyond your horizon means the costs are not recovered in the time you own the loan.

Watch the term as closely as the rate. Keeping the remaining term captures the rate improvement cleanly; taking a fresh 30 years also stretches the debt, which lowers the payment for a reason that is not a saving.

Then read the lifetime cost of both paths, not just the payment. The refinance page shows cumulative cash plus remaining balance on each path, which is the comparison that accounts for a restarted clock.

Question 36

Should I roll the closing costs into the new loan?

Accepted Answer

Rolling them in preserves cash today and converts the fee into a balance that accrues interest for the life of the loan. Paying them in cash spends the cash and leaves the balance clean.

Neither is free, and the tool prices both the same way: costs rolled in raise the loan amount, so they show up in the payment and in the lifetime interest. Costs paid in cash show up as cash out at closing and in the break-even.

The figure to compare is not the payment but the total of cash paid plus balance owed at your expected horizon, which is exactly what the complete break-even tracks.

Question 37

What does a cash-out refinance actually do to my position?

Accepted Answer

It converts equity into cash and into interest bearing debt in the same move. The new balance is the old balance plus the cash taken plus any financed costs, so both the payment and the lifetime interest rise relative to a plain rate and term refinance.

It also raises the loan to value ratio, which can move the loan into a worse pricing tier and can reintroduce mortgage insurance. Lenders generally price cash-out loans above rate and term loans for the same borrower.

The cash is a loan against the house, secured by the house. The tool shows it as what it is: a larger balance, a longer or costlier schedule, and more liquidity today.

Question 38

Are discount points worth paying?

Accepted Answer

Points are prepaid interest: cash at closing in exchange for a lower rate for as long as you hold the loan. That makes it a break-even question rather than a rate question.

Divide the cost of the points by the monthly saving they buy. Holding the loan past that month makes the trade profitable in cash terms; selling or refinancing before it does not. One point on a $300,000 loan is $3,000.

Build the two quotes as separate scenarios and compare total cash out at the horizon you actually expect. A quote with points and one without are not comparable until they are on the same footing.

Question 39

Do I need 20% down?

Accepted Answer

Twenty percent is a threshold, not a rule. Below it, conventional lenders generally require mortgage insurance, which is a monthly cost that protects the lender and buys you nothing except access to the loan.

A larger down payment lowers the loan, the payment and the lifetime interest, and it removes that insurance. It also converts liquid cash into an asset you cannot spend a piece of, and it increases the amount exposed to a fall in the value of the home.

Both effects are measurable here. Vary the down payment on the what-if page and watch the payment, the insurance, the interest and the liquidity left over move together.

Question 40

When does PMI stop?

Accepted Answer

On a conventional loan there are two mechanisms. You may request cancellation once the balance reaches 80% of the original value, and the servicer must terminate automatically at 78% based on the original amortization schedule, provided the payments are current.

Extra principal moves the balance down faster and pulls the request date forward. Cancellation based on the home having appreciated, rather than on payments, normally requires a new appraisal that you pay for.

Some loan programs carry insurance for the life of the loan and never cancel, in which case the only exits are a refinance or a sale. The tool models the loan to value threshold you enter and stops the charge there.

Question 41

What is actually inside closing costs?

Accepted Answer

Lender charges such as origination, underwriting and processing; third party charges such as appraisal, title insurance, survey and recording; any discount points you chose to buy; and prepaid items such as the first year of insurance and the initial escrow deposit.

The prepaid items are your own money moving forward in time rather than a fee. The rest is cash that leaves you and does not become equity, which is why a purchase does not break even on day one.

The tool treats them as cash at closing and as part of the cost side of every break-even, so they are never quietly ignored in a comparison.

Question 42

How much house can I afford?

Accepted Answer

Lenders answer with two ratios. The front end ratio is the full housing payment divided by gross monthly income; the back end ratio adds every other monthly debt payment. Thresholds vary by program and by compensating factors.

Both are measured against gross income, before tax, which is why a payment that qualifies can still feel heavy against take home pay. They also count minimum payments rather than balances, so a long term at a small minimum looks lighter than it is.

Qualifying is a statement about a lender willingness to lend. Whether the rest of your budget survives the payment is a different question, and it is the one the monthly housing figure here is meant to make concrete.

Question 43

Is renting throwing money away?

Accepted Answer

Rent is entirely unrecoverable, which is true and incomplete. Owning has unrecoverable costs as well: interest, property tax, insurance, association dues, maintenance, and the closing and selling costs paid at each end. Only the principal portion of a payment is recoverable, because it becomes equity.

So the honest comparison is unrecoverable cost against unrecoverable cost, not rent against the whole mortgage payment. In the early years of a loan, interest alone can exceed what the rent would have been.

The second half is opportunity cost. The renter invests the down payment and closing costs that the buyer spent, and whoever pays less each month invests the difference, so both paths are fully specified and net worth can be compared at any month.

Question 44

Why do my net proceeds look so much smaller than my equity?

Accepted Answer

Equity uses the market value of the home. Net proceeds subtract what the sale itself consumes: agent commission, seller closing costs, repairs and any concessions to the buyer. Together these commonly run 6% to 10% of the price.

On a $400,000 sale, that gap is $24,000 to $40,000 that the equity figure showed and the closing statement does not. The costs are charged on the price, so they are owed even when the sale loses money.

This is also why short holding periods are expensive: buying and selling within a few years pays both sets of transaction costs out of a small amount of appreciation.

Question 45

How much does my house have to appreciate just to break even?

Accepted Answer

Enough to cover the costs at both ends. Closing costs on the way in and selling costs on the way out mean a sale has to clear several percent of the value before the cash that went in comes back out.

The tool solves for that rate directly, so instead of assuming appreciation and reporting a gain, you read the appreciation the deal requires and judge whether it is plausible in your market. The shorter the holding period, the higher the required rate.

It is a useful sanity check on any purchase justified by future value, because the required number is often larger than the long run average people have in mind.

Question 46

Should the mortgage be part of my debt payoff plan?

Accepted Answer

It can be, and the tool lets you include it or leave it out. A mortgage is usually the largest balance and the lowest rate, which means an avalanche ordering puts it last and a snowball ordering also puts it last.

Including it changes what the debt-free date means. Clearing every consumer debt and clearing the house are different milestones, and the tool reports them separately so a long mortgage does not hide progress on everything else.

The mortgage is also secured, which makes missing a payment on it categorically different from missing one on a card. That is a risk consideration the interest arithmetic does not express.

Question 47

What is the rollover or snowball effect?

Accepted Answer

When a debt is paid off, its minimum payment stops being required. If you keep your total budget constant and redirect that freed minimum to the next target, the amount attacking it grows with every account retired.

This is what makes any payoff plan accelerate toward the end, and it is independent of the order you chose. The waterfall chart shows it as a flat total height with the bands beneath collapsing into fewer, larger payments.

It only works if the freed payment is actually redirected. If it gets absorbed into spending, the projected debt-free date here is optimistic, because holding the budget constant is an assumption about behavior rather than arithmetic.

Question 48

What happens if I only pay the minimums?

Accepted Answer

On an installment loan the minimum is the scheduled payment and the debt retires on time. On revolving credit the minimum is typically a small percentage of the balance plus interest, which stretches repayment over many years and can approach the point where the payment barely exceeds the finance charge.

If a payment is ever smaller than the interest accrued, the shortfall is added to the balance and the debt grows on its own. The tool flags that condition rather than simulating an endless loan, because a plan in that state never ends.

Entering your real minimums and rates makes the difference concrete: the same debts with and without a modest extra payment usually differ by years, not months.

Question 49

Why does the tool report a debt-free date and a mortgage-free date separately?

Accepted Answer

Because they answer different questions about your monthly cash. Consumer debts are often cleared years before the house, and the month the last card closes is when a large amount of monthly obligation disappears.

Keeping them apart also prevents a 30 year mortgage from swallowing the picture. A plan that clears everything except the house in four years looks very different from one that shows a single date in year 27.

The strategy lab reports both on one timeline, along with ending investments and the liquidity left over, so the tradeoffs between the three are visible at once.

Question 50

What return should I enter for investments?

Accepted Answer

There is no right number to hand you, and the tool deliberately does not suggest one. It is an input because it is an assumption, and the whole prepay versus invest comparison pivots on it.

What the tool can show is how much the answer depends on it. Sweep the return on the sensitivity page and read where the two paths cross: if the crossing point sits in the middle of the range you consider plausible, the comparison is not telling you much, and if it sits at the edge, the conclusion is robust to your uncertainty.

Whatever you enter, it is applied smoothly with no volatility, so the invest path in the model never has a bad decade. That is a real difference from an actual portfolio.

Question 51

How does the tool handle taxes on investment gains?

Accepted Answer

With a single flat rate applied to the gain at the end of the horizon. Real treatment depends on the account, the holding period, your bracket, your state and the year you sell, which is more about your situation than a browser tool should assume.

The reason a flat rate exists at all is that ignoring tax entirely would tilt the prepay versus invest comparison, since interest saved by prepaying is not taxed while investment gains generally are. Set the rate to zero to see the pre tax picture.

The mortgage interest deduction is handled the same way and is off by default, because it only produces a benefit when itemized deductions exceed the standard deduction.

Question 52

Why is the mortgage interest deduction off by default?

Accepted Answer

Because for most households it produces no benefit. The deduction only helps to the extent that itemized deductions exceed the standard deduction, and many people who pay mortgage interest every month still take the standard deduction.

Turning it on makes the loan behave as though its rate were lower, which lowers the measured value of prepaying on every page that compares the two. That is a large effect to apply on an assumption.

If you have confirmed that you itemize, turn it on and enter your marginal rate. The settings page warns about the consequence rather than hiding it.

Question 53

Are the numbers adjusted for inflation?

Accepted Answer

Not unless you switch it on. By default every dollar on every chart is a nominal dollar, so a payoff amount in year 25 is stated in year 25 dollars.

That matters most for long horizons. A fixed payment becomes lighter in real terms every year, and a home that grows at the rate of inflation has gained nothing in purchasing power even though the nominal value rose.

Turning the adjustment on divides future amounts by compounded inflation so they are expressed in today dollars. Mixing the two conventions in one comparison is the fastest way to reach a confident wrong answer.

Question 54

Why does no simulation ever spend my emergency reserve?

Accepted Answer

Because the value of a reserve lies in it remaining available. A model that deploys it to squeeze out extra interest savings would be optimizing by removing the thing that protects the plan.

The reserve amount you enter is therefore excluded from every allocation, including the optimizer and the strategy lab. Cash available for strategies is what remains above it.

It is also worth noting that prepaid principal is not a reserve. It cannot be withdrawn without a sale or a new loan, which is precisely the situation a reserve exists to avoid.

Question 55

What are scenarios for?

Accepted Answer

A scenario is a complete, named set of inputs: the loan, the costs, the extra payment rules and the assumptions around them. Saving several lets you compare whole alternatives rather than editing one set of numbers back and forth.

The comparison page puts them side by side on the metrics that usually decide things: payment, payoff date, total interest, total cash out and the balance and equity at five, ten and fifteen years.

It is the right tool for two quotes from different lenders, a 15 year against a 30 year, or the same house with two different down payments.

Question 56

What is the difference between the what-if page and the sensitivity page?

Accepted Answer

The what-if page moves several sliders at once and shows the whole picture updating live. It is for exploring, and for developing a feel for which inputs matter.

The sensitivity page sweeps one variable across a range while everything else stays fixed, and plots the result. It is for answering a specific question: over what range of rates does this conclusion hold.

Together they cover both halves of the same job. Explore until something looks decisive, then sweep that one input to see whether it really is.

Question 57

What does the Strategy Lab do that the other pages do not?

Accepted Answer

It puts every allocation of your extra cash on one timeline. Sending it all to the mortgage, all to the highest rate debt, all to investments, splitting it, or running an avalanche and then switching, are all simulated against the same budget and the same horizon.

The outputs are deliberately plural: debt-free date, mortgage-free date, total interest, ending investments, net position and liquidity along the way. A plan that wins on one of those often loses on another.

Reading it as a ranking would miss the point. It is a map of what your cash can do, and which corner of it you prefer is a judgment about risk and flexibility, not an arithmetic result.

Question 58

How does the optimizer search, and what does it return?

Accepted Answer

It evaluates thousands of complete configurations across the ranges you allow: term, rate, down payment, extra payment and any refinance offers you defined. Every configuration is run through the same engine as the rest of the app, so nothing is approximated.

It then discards every configuration that another one beats on all objectives at once. That step requires no weighting, which is why it is the only filtering the tool does on your behalf.

What comes back is the Pareto frontier plus a handful of representative points along it, such as the lowest lifetime cost, the earliest payoff and the lowest monthly payment. The search runs in a web worker, so the interface stays responsive while it works.

Question 59

Why do my lender numbers differ slightly from these?

Accepted Answer

Small differences usually come from conventions rather than errors. Servicers vary in day count, in when interest accrues relative to the posting date, in how a partial month at origination is handled, and in how an extra payment is applied if it is not clearly designated as principal.

Bigger differences usually come from inputs. Escrow amounts change when a tax bill or a premium changes, mortgage insurance rules vary by program, and a loan that adjusts will diverge from a fixed schedule at its first reset.

If a payoff quote and the schedule here disagree by more than a few dollars, the input to check first is the balance and start date, then whether every fee in the quote is present in the scenario.

Question 60

Does it matter how I tell the servicer to apply an extra payment?

Accepted Answer

It can. An unlabeled extra amount is sometimes applied to the next scheduled payment rather than to principal, which is a very different outcome: it does not reduce the balance and it does not remove future interest.

This tool assumes every extra dollar is applied to principal in the month it is made, which is the behavior that produces the savings shown. Designating a payment as additional principal is how that assumption is met in practice.

It is worth checking on the statement after the first one, since the difference compounds over the life of the loan.

Question 61

My equity chart goes up every month. Am I getting richer every month?

Accepted Answer

Only partly, and the chart cannot tell you which part on its own. Equity rises from two sources: principal you paid, which moved money from cash into the house without changing your net worth at that instant, and appreciation, which is new.

In a flat market the whole rise is conversion. You are more solvent and less liquid than before, and no wealth was created by the act of paying.

What does create wealth over time is the interest you no longer pay because the balance is smaller. That shows up as a lower total cost, not as the step in the equity line, which is why the tool separates the two.

Question 62

Can I check these numbers myself?

Accepted Answer

Yes, and the app is built so you can. Every headline total is a sum or a lookup over the amortization schedule rather than a separate formula, so the table and the metrics can never drift apart.

The amortization table exports to CSV. Open it in a spreadsheet, recompute the interest column as balance times the rate divided by twelve, and the principal column as the payment minus that, and the balance should track to the cent.

The financial engine also carries its own test suite, including a regression that pins the baseline loan at a payment of $1,896.20, total payments of $682,637 and total interest of $382,637.