When will my mortgage actually be paid off?
Four inputs: what you still owe, your rate, the years left, and what extra you can put in. The calculator returns the month the loan is gone, how many months and dollars of interest the extra payments cut against the schedule, and the year-by-year balance on the way down. A one-time lump sum rides along under more assumptions.
Loading the calculator.
How extra principal works
A fixed-rate mortgage charges interest each month on whatever you still owe. The required payment never changes, but its split does: early on, most of it is interest because the balance is large. Every dollar of extra principal skips that line entirely, goes straight to the balance, and stops accruing interest for every month the loan had left. That is why the savings look outsized next to the payment.
At the defaults, a $300,000 balance at 6.65% with 25 years left costs $2,054 a month, and the schedule alone pays $316,149 of interest by Aug 2051. Adding $200 a month, about $2,254 in all, retires it by Nov 2046 instead: 4 years 9 months sooner and $70,464 of interest kept.
The required payment does not fall when you prepay; the term does. You keep writing the same check, just for fewer months, and the last one comes 4 years 9 months early. Tell your servicer the extra is for principal, or it may sit in escrow or be treated as an early next payment instead.
What $200 a month saves, and what more would
The savings scale better than linearly at the front: the first $100 of extra principal buys more months than the fourth, but every level keeps helping. Here is the defaults' $300,000 balance at each level of extra principal.
| Extra each month | Paid off | Sooner by | Interest saved |
|---|---|---|---|
| $100 | Dec 2048 | 2 years 8 months | $40,160 |
| $200 | Nov 2046 | 4 years 9 months | $70,464 |
| $500 | Jul 2042 | 9 years 1 month | $129,707 |
| $1,000 | Jul 2038 | 13 years 1 month | $181,734 |
The schedule alone ends at Aug 2051 after $316,149 of interest; $500 a month ends it at Jul 2042 and keeps $129,707 of that. The control under the result runs this same ladder for whatever balance, rate, and term you enter.
A lump sum now versus more every month
A lump sum and a monthly extra save interest by the same mechanism, but on different clocks. A one-time $10,000 today cuts the balance immediately, so every dollar of it stops accruing interest this month: at the defaults with no monthly extra, that alone moves the payoff to Sep 2049, 1 year 11 months early, and saves $38,966 of interest, with the payment unchanged at $2,054.
The $200 monthly extra reaches $10,000 of contributions only after 50 months, so each dollar starts working later; but the contributions never stop, which is why it ends up saving $70,464, cutting 4 years 9 months, over the whole loan. The two are not rivals: enter a lump sum under more assumptions and a monthly extra above it, and the calculator applies both to one schedule.
What the calculator does not know
Your note. Most conforming fixed-rate mortgages have no prepayment penalty, but some loans do, and a penalty can eat the early savings; the note, not this page, says so. The model also assumes every extra dollar is applied to principal the month you send it, which is exactly the instruction to give your servicer.
Recasting. Some servicers will re-amortize the loan after a large principal payment, lowering the required payment instead of shortening the term. That is a different trade, usually costs a fee, and is not modeled here: this page keeps the payment fixed and lets the term fall.
The rest of your housing bill. Escrow for taxes and insurance rides on top of the payment shown and does not shrink when you prepay, and the tax treatment of mortgage interest depends on whether you itemize. The figures here are principal and interest only.
For agents and scripts
This calculator is built to be used without a browser. Every input is a query parameter on this page, and the same parameters on the JSON twin return the complete answer as a document.
GET /tools/mortgage-payoff.json?balance=250000&rate=6.65&extra=500
The response carries inputs after parsing and clamping, result with the payoff month on the scheduled and accelerated paths, the months and interest saved, the yearly balance rows with the extra payments applied, plus sensitivity tables by monthly extra and by lump size, drivers ranked by effect with a plain sentence each, assumptions that say for every field whether you supplied it and which source the default came from, sources with URLs and as-of dates, warnings, a disclaimer, and in tool the canonicalUrl and jsonUrl that carry only your non-default parameters. The canonical URL is the answer's permanent address; use it when you cite the number.
Parameters, all optional, in any order:
balance($), default $300,000.rate(%), default 6.65%, from Freddie Mac Primary Mortgage Market Survey.yearsLeft(years), default 25 years.extra($ per month), default $200 per month.lump($), default $0.
Values accept plain numbers and loose human formats such as 100k, $100,000, or 6.5%. Unknown parameters are ignored, values outside a field's range are clamped and reported in warnings, and the endpoint never fails on bad input. Responses are cacheable for a day; the defaults change when their sources publish, and tool.version changes when the method does.
Common questions
What does paying an extra $200 a month do to a mortgage?
On a $300,000 balance at the published default rate of 6.65% with 25 years left, $200 of extra principal a month moves the payoff from Aug 2051 to Nov 2046. That is 4 years 9 months sooner, and it saves $70,464 of interest, because every month after the first charges interest on a smaller balance. Enter your own numbers and the page recomputes as you type.
Does paying extra lower my monthly payment?
No. On a standard fixed-rate mortgage the required payment is set by the note and does not change when you prepay; extra principal shortens the loan instead. A one-time $10,000 payment at the defaults leaves the payment at $2,054 but ends the loan 1 year 11 months early. The exception is a recast, where the servicer re-amortizes the reduced balance over the remaining term for a fee; that lowers the payment and keeps the date, and this calculator does not model it.
Is a lump sum now or a bigger monthly payment better?
Dollar for dollar, money that reaches the balance sooner saves more interest, so a lump sum you already have beats drip-feeding the same total. At the defaults, $10,000 today saves $38,966 of interest; $200 a month, which takes 50 months to add up to $10,000, saves $70,464 over the life of the loan because the contributions keep coming. They answer different questions: the lump sum is about money you have now, the monthly extra is about money you free up every month. The calculator takes both at once.
Should I pay extra on my mortgage or invest the money?
This calculator cannot answer that; it only prices one side. Paying extra earns you a guaranteed, tax-free return equal to your mortgage rate, and it cuts risk by ending a fixed obligation sooner. Investing offers a higher expected return that is not guaranteed, keeps the money reachable, and may keep more of a mortgage-interest deduction if you itemize. High-rate debt, an empty emergency fund, or an unmatched employer 401(k) contribution usually outrank both. The honest use of this page is to compute the guaranteed side precisely so you can weigh it against the uncertain one.
Where does the default rate come from?
The 6.65% default is the Freddie Mac Primary Mortgage Market Survey average for a 30-year fixed mortgage as of 2026-08-20. It is a placeholder for a new loan, not yours: an existing mortgage keeps the rate on its note no matter what the survey says this week. Enter the rate from your statement and every figure updates.
Can an agent or a script use this calculator?
Yes. Every input is a query parameter, and the same parameters on /tools/mortgage-payoff.json return the full answer as JSON: inputs, the payoff date on both paths, months and interest saved, year-by-year balances with the extra payments applied, drivers, sensitivity tables by extra amount and lump size, assumptions with sources, and warnings. No browser, no API key.
Sources
- Freddie Mac Primary Mortgage Market Survey, as of 2026-08-20. 30-year fixed-rate mortgage average 6.65%; 15-year 5.95%.
Default values on this page: rate 6.65% (Freddie Mac Primary Mortgage Market Survey). The balance, years left, and extra payment defaults are examples, and the lump sum defaults to zero.
Want the number for your actual finances?
Carlo is a personal finance agent. It knows your accounts, debts, and goals, so instead of a payoff date on an example loan it can weigh the extra payment against your emergency fund, your retirement match, and the other things you are working toward. Text it the question.
ask carlo anything(415) 376-5678
Written by Tejas Shah, Co-founder, Engineering. Building Carlo — the financial model that begins with the decision you're actually weighing. Previously engineering leadership across fintech and consumer startups.
This models extra principal on a fixed-rate, fully amortizing mortgage, with a published default for the rate. It is not a payoff quote or financial advice. Your servicer's payoff statement, and your note's terms on prepayment, are the figures that count.