DebtPayoffTools

Extra Payment Impact Calculator

See what an extra monthly amount and a one-off lump sum do to a debt’s payoff date and total interest.

Last reviewed

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Free · No sign-up · Runs in your browser

An extra payment removes more than its own value from a debt. It also removes every future month of interest that amount would have accrued, which is why a modest overpayment early in a loan has an effect far larger than the sum involved.

This calculator models both an ongoing monthly extra and a one-off lump sum, and reports the interest saved and the months removed.

Your numbers

Results update as you type. Nothing is sent anywhere.

Result

Interest saved

$42,304

Time removed

5.4 years

Months removed
65 months
Current payment
$1,256
New total payment
$1,456
Interest without overpaying
$151,655
Interest with overpaying
$109,351
Original payoff
264 months
New payoff
199 months

Extra amounts are applied to principal after that month’s interest, which is how most servicers handle them. Confirm your servicer does not hold extra funds as a prepaid future payment.

Paying an extra 200 each month removes 65 payments from the schedule.

Accelerated payoff by year

YearPrincipal paidInterest paidRemaining balance
1$6,407$11,069$173,593
2$6,819$10,656$166,775
3$7,257$10,218$159,517
4$7,724$9,751$151,793
5$8,221$9,254$143,572
6$8,750$8,725$134,822
7$9,313$8,163$125,509
8$9,912$7,564$115,598
9$10,549$6,926$105,049
10$11,228$6,248$93,821

How to use the extra payment impact calculator

  1. Enter the current balance, the rate and the years remaining.
  2. Enter the extra amount you can add each month.
  3. Enter any lump sum you plan to apply now.
  4. Compare the new payoff time against the original.

What people use this for

  • Deciding how much extra to pay each month.
  • Working out where a bonus or windfall does the most good.
  • Comparing overpaying a loan against saving the money.
  • Setting a target payoff date and finding the payment it requires.

Worked examples

Every figure below is produced by running this calculator against the example inputs, so the numbers always match the tool.

An extra $200 a month

A $180,000 balance at 6.25% with 22 years remaining, plus $200 a month.

Interest saved
$42,304
Time removed
5.4 years
New payoff
199 months

A $10,000 lump sum as well

The same loan with a lump sum applied immediately alongside the monthly extra.

Interest saved
$59,124
Months removed
83 months
Interest with overpaying
$92,531

Early overpayments are worth far more

The saving from an extra payment is the interest it prevents over the remaining life of the loan. The earlier it is made, the more months of interest it removes - which is why the same $10,000 saves several times more in year two than in year fifteen.

The corollary is that the rate matters as much as the timing. Overpaying a 22% card removes far more interest than overpaying a 6% mortgage, which is where extra money usually belongs first.

Check how the lender applies it

Extra funds should reduce the principal immediately. Some lenders instead hold them as a prepaid future instalment, which advances the due date without saving any interest at all.

Ask, and where possible mark the payment as principal-only. On many loans it is the difference between a real saving and none.

Methodology and assumptions

What this calculator does, and what it deliberately does not do.

  • The baseline payment is the amortising payment for the balance over the remaining term.
  • The lump sum is applied to the balance immediately; the extra monthly amount is applied to principal after interest each month.
  • The saving is the difference in total interest between the baseline and the accelerated schedule.
  • Results are estimates. Real quotes depend on credit, income, property, loan programme and lender pricing at the time of application.
  • Nothing you type is transmitted or stored - the calculation runs entirely inside your browser.

This calculator is provided for informational and educational purposes only. Results are estimates and may not reflect actual rates, fees, taxes, or market conditions.

This website is not a lender, a mortgage broker or a financial adviser. It does not originate loans, does not accept applications and does not forward your details to anyone.

Actual loan terms depend on credit history, income, the property, the loan programme and lender pricing at the time of application. Only a lender can tell you what you qualify for.

Frequently asked questions

Should I overpay the mortgage or invest?

Overpaying is a guaranteed return at the loan rate; investing is uncertain and potentially higher. Neither answer is universal, and the loan rate is the number to compare against.

Will my payment go down?

Usually not. The term shortens and the payment stays the same, unless the lender recasts the loan on request after a large lump sum.

Is there a prepayment penalty?

Most consumer loans allow overpayment freely, but some carry charges. Check the agreement before making a large payment.

Which debt should I overpay first?

The highest rate, almost always. The debt payoff calculator handles multiple debts and shows the order.

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