Mortgage Duration Calculator
Mortgage duration here means one thing: how long your loan actually lasts. Enter your current balance, rate and monthly payment, add an extra amount each month or a one-time lump sum, and the calculator simulates the loan month by month to give you the payoff date, the total interest, and exactly how much time and interest the extras save against the standard schedule.
Fixed-rate amortization. The lump sum is applied before the first payment. Tell your servicer to apply extras to principal, not future payments.
Quick Answer
On a $300,000 balance at 6.5% with a $1,896.20 monthly payment, adding $200 a month from November 2026 ends the loan in November 2049: 277 payments over 23 years 1 month, with $279,186.15 of interest. Against the standard schedule (361 payments, $382,636.53 of interest), the extra $200 saves 7 years and $103,450.38. The calculator above is pre-filled with this exact case.
Key takeaways
- Duration here means time until payoff, counted in payments. It is not bond duration, and nothing here prices a security.
- Small and steady wins: $100 a month extra on the example loan saves $60,995.81 and 4 years 1 month.
- A lump sum lands before month one, so per dollar it removes more interest than the same money dripped in monthly.
- Extras only save interest when your servicer applies them to principal. Get that instruction on record and check the next statement.
- Quick Answer
- How to use this mortgage duration calculator
- What duration means here, and what it does not
- How the payoff math works
- Worked example: $300,000 at 6.5% with $200 extra a month
- Extra monthly, lump sum, or a recast: three different levers
- Make sure your servicer applies extras to principal
- What competing calculators miss
- The honest limits of this calculator
- Frequently asked questions
- Add This Calculator to Your Website
- References
How to use this mortgage duration calculator
Enter the loan as it stands today, not as it started. The tool needs your current balance and your actual required payment, which is what makes it work mid-loan, years after closing.
- Balance and rate: copy the current balance from your latest statement and your fixed APR. If you only know the original loan details, the mortgage payment calculator works out the principal and interest payment for a balance, rate and term.
- Monthly payment: enter the principal and interest part only. Leave out the escrow portion for taxes and insurance, because escrow money never touches the balance.
- Extra per month: the amount you can genuinely send every month. Use 0 to see the untouched schedule first; that baseline is what every saving is measured against.
- Lump sum: a one-off amount available now, such as a bonus, a tax refund or the proceeds of selling a car. The tool applies it before the first simulated month.
- First payment month: the month your next payment falls due. The payoff date counts forward from it, and the green badge in the results restates the saving in one line for copying or sharing.
What duration means here, and what it does not
Here, duration is the remaining life of your mortgage: the count of monthly payments until the balance reaches zero, expressed in years, months and a payoff date. That is the borrower meaning of the word, and it is the only one this calculator computes.
It is not the bond market meaning. In fixed income, Macaulay duration (after Frederick Macaulay’s 1938 study of bond yields for the National Bureau of Economic Research) is a present-value-weighted average of the times at which a bond pays its cash flows, and modified duration converts that into a price sensitivity: roughly how much a bond’s price moves when yields change by one percentage point. A mortgage borrower has no price to revalue and no yield curve to hedge, so neither measure answers the household question, which is simply: when is this loan gone, and what will it cost me on the way? If you arrived here expecting rate-sensitivity analysis for a bond or a mortgage-backed security, this is the wrong tool, and it is better to say so plainly than to dress a payoff simulator up as one.
How the payoff math works
The calculator runs an honest month-by-month simulation of the loan, the same arithmetic your servicer’s amortization schedule uses. There is no shortcut formula hidden inside it.
Your balance, minus any lump sum, before month one.
Balance × (annual rate ÷ 12).
The rest of the payment cuts principal.
The month the balance clears is the payoff date.
Payoff: the first month in which the new balance reaches zero. The final payment is only as large as the remaining balance plus its interest.
Two details are worth knowing. First, the simulation was cross-checked against the closed-form amortization formula, n = −ln(1 − P·r ÷ payment) ÷ ln(1 + r), and the two agree to the payment on every example in this article. Second, the standard schedule for the example loan runs 361 payments, not 360. The exact 30-year payment on $300,000 at 6.5% is $1,896.2041, and the entered $1,896.20 falls a fraction of a cent short each month, so a small stub balance survives payment 360 and is cleared by a smaller 361st payment. Real servicer schedules do exactly the same thing when a payment is rounded down, which is why your own payoff month can sit one month past the tidy anniversary.
Worked example: $300,000 at 6.5% with $200 extra a month
A borrower owes $300,000 at 6.5%, pays $1,896.20 a month, and can add $200. Every figure below is this calculator’s own output for those inputs, starting November 2026.
| Scenario | Payoff date | Duration | Total interest | Total paid |
|---|---|---|---|---|
| Standard schedule, no extras | November 2056 | 30 years 1 month (361 payments) | $382,636.53 | $682,636.53 |
| With $200 extra a month | November 2049 | 23 years 1 month (277 payments) | $279,186.15 | $579,186.15 |
The ladder below runs the same loan at four extra amounts. Read it as the price of time: each additional $100 a month buys fewer months than the last, because the loan it is shortening is already shorter. Savings are computed before rounding, so a row can differ by a cent from subtracting the rounded totals.
| Extra per month | Payoff date | Duration | Total interest | Interest saved | Time saved |
|---|---|---|---|---|---|
| $0 | November 2056 | 30 years 1 month | $382,636.53 | n/a | n/a |
| $100 | October 2052 | 26 years 0 months | $321,640.71 | $60,995.81 | 4 years 1 month |
| $200 (worked example) | November 2049 | 23 years 1 month | $279,186.15 | $103,450.38 | 7 years 0 months |
| $300 | August 2047 | 20 years 10 months | $247,519.43 | $135,117.10 | 9 years 3 months |
| $500 | April 2044 | 17 years 6 months | $202,875.11 | $179,761.42 | 12 years 7 months |
Extra monthly, lump sum, or a recast: three different levers
All three routes attack the same balance, but they buy different things. Extra monthly payments and lump sums shorten the term; a recast keeps the term and cuts the payment instead.
Extra every month
$200 a month on the example loan: debt-free November 2049, $103,450.38 of interest avoided. You can pause it in a bad month, which is its real advantage. The cost is discipline over decades, and roughly $55,000 of extra cash sent in total.
One lump sum now
$10,000 today on the same loan saves $53,917.43 and 2 years 10 months, because it stops a full $10,000 from accruing interest from month one. A $24,000 lump sum saves $113,457.41, more interest than the $200-a-month route, from far less cash sent. The catch: the money is locked into the house.
Recast after a lump sum
Many servicers will re-amortize a reduced balance over the remaining term for a modest fee. The payoff date stays where it was and the required payment falls, which helps cash flow but saves far less interest. This calculator models the first two levers, not a recast.
Borrowers running an offset account or a HELOC sweep are pulling the first two levers on a schedule, which is the strategy the mortgage accelerator calculator examines. The arithmetic underneath is identical to the simulation above: principal removed earlier stops charging interest sooner.
Make sure your servicer applies extras to principal
An extra payment only shortens your loan if it reduces principal. Sent without instructions, extra money can be used to advance your due date or held against future scheduled payments, and neither saves a cent of interest.
The Consumer Financial Protection Bureau makes the same point in its guidance on what your mortgage servicer must comply with under federal rules: check that your loan allows extra payments and that they are applied to principal rather than interest, noting that even $100 more per month may reduce the loan term by several years. Put “apply to principal” in the payment notes or the servicer’s online designation field, then confirm on the next statement that the balance dropped by more than the scheduled principal. Before sending a large lump sum, also check for a prepayment penalty: the CFPB’s explainer on what a prepayment penalty is covers the basics, and federal rules bar penalties on most residential mortgages made since January 2014 and tightly cap the rest. If your rate sits well above current rates, run the other comparison too: the cost to refinance mortgage calculator weighs closing costs against a lower rate, which is a different trade from prepaying the loan you have.
What competing calculators miss
The payoff and accelerator tools ranking for this keyword share one weakness: their published examples do not survive being re-run. Each claim below was checked against the standard amortization simulation used by the calculator above.
- BraveCalculator’s mortgage accelerator and payoff date pages give two different wrong answers to the same loan. A $300,000 loan at 5% over 30 years with $200 extra a month is said to end in 24 years 1 month saving “over $54,000” on one page, and in August 2044, 5 years 5 months early, saving $45,870 on the other. Run correctly with the $1,610.46 payment those pages quote, it ends after 283 payments (23 years 7 months, July 2043 from a January 2020 start), 6 years 6 months early, saving $69,211.44.
- CalcPocket’s extra payment table understates every row for a $300,000 loan at 6.5%. It shows $100 extra a month producing a 26 year 10 month payoff and $40,185 saved; the correct figures are 26 years exactly and $60,995.81. At $1,000 extra it shows 15 years 8 months and $178,006 saved, against a correct 12 years 9 months and $241,164.79.
- Recast Mortgage Calculator handles the mid-loan case well and offers a year-by-year balance table, which this page does not. Its cost is reconstruction: it rebuilds your balance from the original loan and the number of payments made, so any past extra payments or a past recast throw its starting point off. This tool starts from the balance on your statement today and the payment you actually make.
- ConvertersZone gets the same example loan right to within a dollar or two, and deserves the credit. The gap is scope: its extra payment comparison is a fixed table for one example loan inside a general mortgage calculator, with no lump sum input and no payoff month counted from your own start date.
- The gap this page fills: current balance plus your real payment (not a payment re-derived from a term), extra monthly and lump sum in the same run, a named payoff month, and worked numbers that match the closed-form formula to the payment.
The honest limits of this calculator
Every shortcut in the tool is listed here rather than buried. Knowing them makes the output more useful, not less.
- Fixed rate, principal and interest only. Adjustable rates, escrow, taxes, insurance and PMI are outside the model. Your total monthly outlay is higher than the payment entered here.
- The rate must be above zero. A 0% loan is rejected with an error rather than simulated, a known gap in the tool.
- The too-low payment check is conservative. It compares your base payment alone against one month of interest on the full balance, before the extra amount and lump sum are counted. A run can therefore be refused even when the combined payment would have amortized the loan, for example a small base payment paired with a large lump sum.
- The simulation caps at 1,200 months (100 years). A loan that would need longer is reported at the cap. Treat a result of 100 years 0 months as “longer than a century,” not as a true payoff date.
- Steady behaviour is assumed. The extra amount is sent every single month and the rate never changes. Missed extras push the real payoff later than the date shown.
Frequently asked questions
Whatever you can sustain every month. On the worked example loan, $100 a month extra saves $60,995.81 in interest and shortens the loan by 4 years 1 month, while $200 a month saves $103,450.38 and 7 years. A smaller amount you never skip beats a larger one you abandon after a few months.
Not always. Some servicers advance your due date or hold extra money against future scheduled payments, which saves no interest at all. Tell the servicer in writing to apply the extra amount to principal, then check the next statement to confirm the balance fell by more than the scheduled principal.
Per dollar, the lump sum wins because it removes principal before month one. A $10,000 lump sum on the worked example saves $53,917.43 in interest and 2 years 10 months. The catch is liquidity: money sent to principal is hard to get back, while a monthly extra can be paused, so keep an emergency fund first.
The calculator stops with an error when your base monthly payment does not exceed one month of interest on the full balance, because the balance would never fall. Note that the check uses the base payment and the full balance on their own: it runs before your extra amount and lump sum are counted, so a run can be rejected even when the combined payment would have worked.
Paying extra earns a guaranteed return equal to your mortgage rate, with zero market risk. Investing may return more over long periods but can also fall, and the comparison changes if your mortgage interest is deductible. Many households split the difference, and there is no single right answer.
By month-by-month simulation: each month the balance accrues interest at your annual rate divided by 12, then your payment plus extra is subtracted, until the balance reaches zero. The payoff month counts forward from your first payment month, and the count includes the final, smaller payment.
Yes. In this tool the lump sum reduces the balance before the first month of interest accrues, which is the best case for a lump sum and matches sending it with, or just before, your first simulated payment. A lump sum sent months later saves slightly less.
They are excluded. This calculator models principal and interest only, so your escrow charges continue unchanged whatever the extras do. Paying the loan off early ends the mortgage, not the tax and insurance bills, which you then pay directly.
Yes, with a large enough extra. On a $250,000 loan at 6.5 percent with the standard payment of $1,580.17, it takes about $598 extra a month to finish in exactly 180 payments (15 years 0 months). The often-quoted $490 figure is not enough: it lands at 197 payments, or 16 years 5 months, as this calculator shows.
No. Bond duration (Macaulay or modified duration) is a weighted average time to a bond’s cash flows and measures price sensitivity to rate changes. This page uses duration in the plain borrower sense: how long the mortgage lasts until payoff, in years, months and payments. Nothing here prices a bond or a mortgage-backed security.
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References
- Consumer Financial Protection Bureau. Your mortgage servicer must comply with federal rules. Accessed October 22, 2026.
- Consumer Financial Protection Bureau. What is a prepayment penalty?. Accessed October 22, 2026.
- Electronic Code of Federal Regulations. 12 CFR 1026.43: Minimum standards for transactions secured by a dwelling. Accessed October 22, 2026.
- Electronic Code of Federal Regulations. 24 CFR 203.22: Prepayment privilege for FHA-insured mortgages. Accessed October 22, 2026.
- Internal Revenue Service. Publication 936: Home Mortgage Interest Deduction. Accessed October 22, 2026.
- Freddie Mac. Primary Mortgage Market Survey. Accessed October 22, 2026.
- Federal Reserve Bank of St. Louis, FRED. 30-Year Fixed Rate Mortgage Average in the United States (MORTGAGE30US). Accessed October 22, 2026.
- Board of Governors of the Federal Reserve System. Statistical Release H.15: Selected Interest Rates. Accessed October 22, 2026.
- Macaulay, Frederick R. Some Theoretical Problems Suggested by the Movements of Interest Rates, Bond Yields and Stock Prices in the United States since 1856. National Bureau of Economic Research, 1938. Accessed October 22, 2026.
- Federal Housing Finance Agency. House Price Index (HPI). Accessed October 22, 2026.