Your real monthly payment — principal, interest, property tax, insurance and PMI together — plus what an extra payment saves and the month PMI drops off. Most mortgage calculators return principal and interest only, which is typically 25–30% below what actually leaves your account.
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The formulas
A $400,000 home with 20% down leaves a $320,000 loan. At 6.5% over 30 years, principal and interest come to $2,022.62. Add $400 property tax and $150 insurance monthly and the real payment is $2,572.62 — 27% higher than the figure a basic calculator returns. Over the full term the interest alone totals $408,142, more than the loan itself.
Why extra payments do so much
An extra payment goes entirely against principal, and every dollar of principal removed also removes all the future interest that dollar would have generated. The effect compounds backwards, which is why the numbers look implausible at first:
| Extra per month | Paid off in | Interest saved |
|---|---|---|
| Nothing | 30 years | — |
| $200 | 23 years 5 months | $105,429 |
| $500 | 18 years | $185,552 |
Based on the $320,000 example above at 6.5%.
Two hundred dollars a month — $72,000 over the shortened term — removes $105,429 of interest and six and a half years of payments. The saving exceeds the amount paid, because every extra dollar removes the interest that dollar would have carried for the rest of the term. That is an avoided cost at the loan’s own rate, which is a different thing from an investment return: it is certain, but it is not income, and mortgage interest may be deductible if you itemise, which narrows the gap.
One condition: confirm your lender applies extra payments to principal rather than holding them against the next instalment. Some require it to be specified. If it goes to the next payment instead, none of this happens.
APR is the number to compare, not the rate
Lenders advertise the interest rate. APR helps when comparing loans of similar term, because it folds in points and lender fees that the headline rate leaves out. It has a real limitation: it assumes you hold the loan to term, so it flatters an offer with high upfront fees if you sell or refinance early — and that is what most people do. Compare APR alongside the fee schedule, not instead of it.
A $320,000 loan at 6.5% with one discount point ($3,200) and $3,500 in lender fees has an APR of 6.705%. The advertised rate understated the cost by 0.205 points — about $13,000 over thirty years. A competing offer at 6.6% with no fees is cheaper, despite the higher headline rate.
This is why the Loan Estimate is legally required to state APR. Put the APRs side by side, and read them alongside the fee schedule rather than instead of it. APR is usually more useful than the note rate when the terms match, because it folds in points and lender costs. It assumes you hold the loan to term, though, so an offer with high upfront fees looks better under APR than it will turn out to be if you sell or refinance before the break-even point — and the note rate is what governs how the balance actually compounds. Both numbers answer different questions.
Mortgage insurance differs sharply by program
The insurance rules are where borrowers most often make an expensive assumption, because the four programs behave completely differently:
| Program | Monthly insurance | Does it cancel? |
|---|---|---|
| Conventional | PMI, ~0.3–1.5% | Yes — on request at 20% equity, automatically at 22% |
| FHA | MIP, ~0.55% | No — for the life of the loan if you put under 10% down. Removing it requires refinancing |
| VA | None | Not applicable — a one-off funding fee instead |
| USDA | Annual fee, ~0.35% | No — runs for the life of the loan |
On a $320,000 FHA loan, MIP at 0.55% costs $146.67 monthly — $52,800 across thirty years. The equivalent conventional PMI would cancel around year eight, costing roughly $13,600. That $39,000 difference is invisible in the monthly payment comparison, which is exactly why it catches people.
FHA is still the right choice for many buyers — the credit and down-payment requirements are genuinely easier. But if you can qualify conventionally with 20% down, the lifetime difference is substantial and worth calculating before deciding.
Biweekly payments: the quiet extra payment
Paying half your monthly amount every two weeks produces 26 half-payments a year — which is 13 monthly payments, not 12. That extra payment goes entirely to principal.
On the $320,000 example, biweekly clears the loan in 24.2 years instead of 30 and saves $93,997 in interest, with no meaningful change to your monthly budget. The mechanism is not a discount from the lender: you are simply making thirteen monthly payments a year instead of twelve, and the interest saving follows from paying principal down sooner.
Should you take a shorter term?
Shorter terms carry lower rates and far less total interest — but the monthly commitment is fixed and unforgiving. The real numbers on a $320,000 loan:
| Term | Monthly P&I | Total interest | Against 30 years |
|---|---|---|---|
| 30 years @ 6.5% | $2,023 | $408,142 | — |
| 20 years @ 6.3% | $2,348 | $243,593 | −$164,549 |
| 15 years @ 5.9% | $2,683 | $162,955 | −$245,187 |
| 10 years @ 5.8% | $3,521 | $102,472 | −$305,670 |
Rates shown reflect the typical spread between terms; your quotes will differ.
The 15-year saves $245,187 for $660 more each month. That is a strong trade on paper — but it is a contractual obligation, and a job loss in year seven does not care how good the arithmetic was.
Take the 30-year, then pay it at the 15-year amount voluntarily. You capture nearly all the interest saving while retaining the right to drop back to the lower required payment in a bad year. The cost is the slightly higher rate on the 30-year — typically 0.5%, which the flexibility usually justifies.
What a rate change does to your budget
Buyers tend to think in home prices. Lenders approve on payment, which means the rate quietly sets your price ceiling. Holding the payment fixed at $2,023:
| Rate | Loan you can carry | Against 6.5% |
|---|---|---|
| 5.0% | $376,777 | +17.7% |
| 5.5% | $356,227 | +11.3% |
| 6.0% | $337,356 | +5.4% |
| 6.5% | $320,000 | — |
| 7.0% | $304,015 | −5.0% |
| 7.5% | $289,270 | −9.6% |
Every half point moves your buying power by roughly 5%. On this loan that is $16,000 of house per half point — which is why locking a rate matters, and why waiting for prices to fall while rates rise often leaves you worse off than buying now.
Pay it down, or invest the difference?
The most common question after seeing the extra-payment numbers, and most articles answer it with a comparison that does not hold up.
The usual version puts $105,429 of interest saved against the value of a portfolio built from the same $200 a month. Those are different units — nominal dollars spread across twenty-three years against a single balance at one date — and the comparison also ignores what happens after the loan is gone. Someone who finishes early stops paying $2,022.62 a month and can invest that instead, for the six years and seven months they bought back.
Comparing the same cash flows over the same thirty years gives a different answer:
| Annual return | Invest $200 for 30 years | Prepay, then invest the freed payment | Difference |
|---|---|---|---|
| 4% | $138,810 | $200,496 | Prepay +$61,686 |
| 5% | $166,452 | $207,429 | Prepay +$40,977 |
| 6% | $200,903 | $214,671 | Prepay +$13,768 |
| 6.42% | $217,000 | $217,000 | Break-even |
| 7% | $243,994 | $222,239 | Invest +$21,755 |
| 8% | $298,072 | $230,148 | Invest +$67,924 |
| 10% | $452,098 | $247,060 | Invest +$205,038 |
The break-even sits at 6.42%, just under the loan’s own rate. Below it, prepaying wins; above it, investing does, and the margin widens quickly. A table that starts at 7% — as most do, including an earlier version of this one — shows only the half of the range where investing wins.
Investing wins only above the loan’s own rate above the mortgage rate, and historically equities have delivered that. But the comparison is not like-for-like: the mortgage saving is certain, the portfolio is not, and a decade of poor returns is entirely possible.
Three things settle it in practice rather than in theory. Employer match first — an immediate 50–100% return beats both. High-interest debt first — credit card debt at 20% makes this whole comparison irrelevant. And your own tolerance: someone who will lose sleep over market volatility is better served by the certain one, whatever the spreadsheet says.
Step-by-step guide
- Enter the home price and what you can put down. The percentage updates as you type — below 20% triggers PMI, which the calculator adds automatically.
- Use a realistic rate. Advertised rates assume excellent credit and often include discount points. Add roughly 0.25–0.5% for a realistic figure until you have a quote in writing.
- Fill in tax and insurance. Property tax is on the listing or the county assessor's site; if not, 1.1% of the price annually is a reasonable placeholder. Insurance runs $1,200–$2,400 for most homes.
- Try an extra payment. Enter $100, then $200. The interest saved is usually the moment the whole picture changes.
- Compare terms. Switch from 30 to 15 years — the payment rises noticeably, the total interest roughly halves.
Common mistakes
Mortgage terms, in plain language
The vocabulary lenders use, translated. Worth reading once before a first conversation with a broker.
| Term | What it means |
|---|---|
| APR | The interest rate plus lender fees, expressed annually. It is the number to compare between lenders — a low rate with high fees can carry a worse APR than a higher rate without them |
| Points | Prepaid interest. One point costs 1% of the loan and typically cuts the rate by about 0.25%. Worth it only if you keep the loan past the break-even, usually 4–6 years |
| LTV | Loan-to-value — the loan as a percentage of the home's value. Above 80% triggers PMI; below it, better rates become available |
| DTI | Debt-to-income — all monthly debt payments as a share of gross income. Most lenders cap around 43%, some to 50% with compensating factors |
| Escrow | An account the lender holds to pay your tax and insurance. Your payment funds it monthly; a shortfall after a tax reassessment raises the payment |
| Amortisation | The schedule splitting each payment between interest and principal. Front-loaded toward interest, which is why early extra payments matter most |
| Rate lock | A guarantee the quoted rate holds for a period, usually 30–60 days. Free at most lenders; extensions are not |
| Loan Estimate | A standardised three-page disclosure lenders must provide within three days of application. Compare these, not marketing pages |
| Recast | Re-amortising after a large lump payment, lowering the monthly figure without refinancing. Cheaper than a refinance and often overlooked |
| PMI vs MIP | PMI applies to conventional loans and can be cancelled. MIP applies to FHA loans and usually cannot be removed without refinancing — a significant difference over thirty years |
Frequently asked questions
What is included in a mortgage payment?
Four components, known together as PITI: principal, interest, taxes and insurance. Principal reduces the balance, interest is the lender's charge, and tax and insurance are usually collected monthly into an escrow account the lender pays out from. Add PMI if your down payment was under 20%, and HOA fees where they apply. Only the first two are what a basic mortgage calculator returns.
How much house can I afford?
The common guideline is that total housing costs stay under 28% of gross monthly income, and all debt payments under 36% — the ratios most lenders underwrite to. Work from the full PITI figure rather than principal and interest, or the answer comes out about 30% too optimistic. Our Home Affordability Calculator works backwards from income and existing debts.
When does PMI come off?
You can request cancellation at 20% equity, and under US federal law the lender must remove it automatically at 22% based on the original amortisation schedule. Extra payments reach that point sooner, and so does appreciation — though using appreciation usually requires paying for an appraisal. The calculator shows the month you hit 20% on the scheduled payments alone.
Is a 15-year mortgage better than a 30-year?
It costs far less in total interest and usually carries a slightly lower rate, but the monthly payment is roughly 40% higher and that commitment is fixed. A middle path many people prefer: take the 30-year for the flexibility of a lower required payment, then pay it like a 15-year voluntarily. You capture most of the interest saving while keeping the option to fall back in a difficult year. Switch the term above to compare both.
Should I put down more than 20%?
Twenty percent avoids PMI, which is the sharp threshold. Beyond that it becomes an ordinary comparison: money in the house avoids a cost equal to your mortgage rate, while money invested might earn more with risk. At 6.5%, paying down is a strong risk-free return. The stronger argument against going higher is liquidity — equity is difficult to access quickly, and an emergency fund matters more than a marginally smaller payment.
Why is my lender's quote higher than this?
Usually escrow. Lenders collect a cushion — typically two months of tax and insurance — and may require prepaid interest to the first of the following month. Your rate may also differ from the advertised one once credit score and points are applied. Ask for the Loan Estimate, which itemises every component and is legally required to be provided.
Do extra payments really save that much?
Yes, and the mechanism is straightforward once you see it. Early in a loan almost all of each payment is interest — on the example above, the first payment is $1,733 interest and $290 principal. An extra $200 goes entirely to principal, removing that balance and every future interest charge it would have carried. Doing it early matters far more than doing it later, because there is more remaining interest to cancel.
Is my information stored?
No. Every calculation runs in your own browser and nothing is transmitted or saved. That matters here — income, savings and the price of a home you are considering are exactly the details you should not be handing to a website.
Sources
- Consumer Financial Protection Bureau. What is a debt-to-income ratio? and the Ability-to-Repay rule under Regulation Z, 12 CFR 1026.43. The source of the 43% figure lenders work to.
- US Department of Housing and Urban Development. FHA Single Family Housing Policy Handbook 4000.1, Appendix 1.0. The upfront and annual MIP rates and the rule that annual MIP runs for the life of the loan above 90% LTV.
- Homeowners Protection Act of 1998, 12 U.S.C. 4901 et seq. Requires a lender to cancel PMI automatically at 78% of original value and on request at 80%, which is the rule the PMI drop-off month here follows.
- Truth in Lending Act, Regulation Z, 12 CFR 1026.22 and Appendix J. The definition of APR and the method used to fold fees and points into it, which is why the APR here differs from the note rate.
- Formula. The monthly principal and interest payment is
P × r × (1 + r)n ÷ ((1 + r)n − 1), whereris the annual rate divided by twelve andnthe number of payments. APR is solved iteratively for the rate that makes the discounted payments equal the amount financed.
Every figure on this page is computed by running the formulas above rather than quoted, so the article and the calculator cannot disagree. Rates, fees and escrow practice vary by lender and by state, and the thresholds cited are US federal rules. A lender’s own figure is the one that binds.
Related calculators
See the full list of Financial calculators, or try:
- Home Affordability Calculator — works backwards from your income
- Amortization Schedule Calculator — the full year-by-year table
- Mortgage Payoff Calculator — model extra payments in detail
- Refinance Calculator — whether a new rate is worth the closing costs
- Closing Cost Calculator — the cash you need beyond the down payment