Extra Payment Calculator — Pay Off Early, See Exact Savings
Enter your remaining loan details plus any extra monthly or annual amount, and see your new payoff date against the original one, how many months you cut, and the exact interest you save. Results update live as you type.
Calculator
Results
| Year | Standard balance | With extras |
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How Extra Payments Attack Your Loan Balance
Every regular mortgage payment is split two ways: interest owed for the month, and everything else against principal. Early in a 30-year loan the interest slice is huge — on the default example, the very first $1,516.96 payment carries $1,300.00 of interest and only $216.96 of principal. That is why the balance falls so slowly at first.
An extra payment changes the order of battle. It carries no interest of its own, so it goes entirely to principal. And every dollar of principal you remove early stops generating interest for every remaining month of the loan. The calculator models exactly this: it amortizes your balance month by month, adds your extra amount directly to principal in each month you pay it, and stops the clock when the balance hits zero.
Two things follow from the math. First, extra payments made in the early years are worth the most, because they block the most future interest. Second, the effect is not linear in time — $100 extra a month does more damage per dollar in year 2 than in year 22, because there is more remaining interest to avoid.
Example: $100 a Month, 30 Years, 6.5%
Take the default inputs: a $240,000 loan at 6.5% with 30 years remaining, plus $100 extra every month. Run through the calculator, these are the exact numbers:
- Standard payment: $1,516.96; with the extra, $1,616.96 a month
- Original payoff: 360 months (30 years) with $306,106.77 total interest
- New payoff: 302 months (25 years, 2 months) — 58 months, nearly 5 years, early — with $247,755.30 total interest
- Interest saved: $58,351.47 — across the shortened schedule you pay $30,200 of extra principal in total, and that early principal avoids $58,351 of interest the standard plan would have charged
The balance comparison at every fifth year, exactly as the calculator's table shows it:
| Year | Standard balance | With $100 extra monthly |
|---|---|---|
| 5 | $224,666.35 | $217,598.95 |
| 10 | $203,462.70 | $186,622.39 |
| 15 | $174,141.94 | $143,787.46 |
| 20 | $133,596.68 | $84,554.59 |
| 25 | $77,529.99 | $2,646.34 |
| 30 | $0.00 | $0.00 |
By year 20 the accelerated borrower owes $49,042 less, and the loan dies nearly five years before the standard schedule's final payment.
Extra Monthly vs Extra Annual: Which Saves More?
Both schedules put the same $1,200 a year toward principal, but they do not save the same interest. Money paid earlier removes balance earlier, and removed balance earns no interest. The monthly route pays $100 in month 1; the annual route pays $1,200 in one shot, and its timing matters:
- $100 extra every month: payoff in 302 months, interest saved $58,351.47.
- $1,200 once a year, paid at the loan's anniversary (start of the loan year): payoff in 301 months, interest saved $60,614.14 — slightly better than monthly, because $1,200 lands up front each year.
- $1,200 once a year, paid in the last month of each loan year: payoff in 304 months, interest saved $56,110.17 — the worst timing of the three, since the money sits idle for up to 11 months.
All three numbers are computed by the same amortization engine as the calculator above, on the same $240,000 / 6.5% / 30-year loan. The lesson is not that annual payments are bad — they are nearly as good — but that timing shifts the outcome. If your bonus arrives in January, applying it right away beats parking it in a checking account until December. A smaller amount applied sooner is usually worth more than a larger amount applied later.
One practical note: a recurring annual lump sum is easier to commit to than a higher monthly debit, and the calculator above handles both — enter the bonus under extra annual payment, or split it under extra monthly payment, and compare the payoff dates directly.
FAQ
Does an extra payment go to principal automatically?
Not always. Many servicers apply unexpected extra amounts to the next payment due, or park them in a suspense account, unless you mark the payment as applying to principal. When you make an extra payment, include a note such as "apply to principal" and check your next statement that the balance dropped by the full extra amount.
Should I refinance instead of making extra payments?
Extra payments and refinancing solve different problems. Extra payments are free, reversible in effect, and make sense when your rate is already decent and you simply want the loan gone sooner. Refinancing makes sense when market rates are clearly below your current rate and the closing costs pay for themselves in a reasonable time. If your rate is high, compare both with real numbers before choosing.
How much can I really save by paying $100 extra a month?
It depends on your balance, rate, and remaining term. On the default example used on this page ($240,000 at 6.5% over 30 years), adding $100 a month saves $58,351 in interest and pays the loan off 58 months, or nearly 5 years, early.
Is it better to pay extra monthly or once a year?
Paying the same total amount earlier and more often always saves more interest, because the balance shrinks sooner. Splitting $1,200 a year into $100 a month beats waiting and paying $1,200 at the end of the year, although the difference is modest. The earlier in the year a lump sum lands, the more it saves.
Do prepayment penalties apply to extra payments?
Most mortgages written in the United States today have no prepayment penalty, and federal rules restrict penalties on most loans made after 2014. Check your loan documents or ask your servicer to confirm before accelerating payments, especially on older or non-standard loans.
Want the Biweekly Version?
If instead of a fixed extra amount you want to see what half-payments every two weeks do to your loan, use the Biweekly Mortgage Calculator. For the two prepayment patterns compared head to head on the same loan, read Biweekly vs Extra Payments. The AmortWise homepage lists both tools side by side, and the terms of use explain how to interpret the estimates.