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HomePaymentHQ

Extra Payment Mortgage Calculator

See how a few extra dollars a month — or a one-time lump sum — can erase years of interest from your loan.

Your loan

$
%

Extra payments

$
Your current scheduled P&I is $2,070/mo.
$
Month from now when the lump sum is applied.
Interest saved
$89,810
Pay off 5 yr 9 mo earlier.
Months saved
69
New payoff
Aug 2048
Original interest
$375,672
New interest
$285,862

Balance over time

$320,000$240,000$160,000$80,000$00y5y10y15y20y25y
Original schedule With extra payments

Side-by-side comparison

OriginalWith extraDifference
Payoff dateMay 2054Aug 20485y 9m sooner
Total interest$375,672$285,862−$89,810
Months to payoff336267−69

How prepayment math works

Each month, a portion of your scheduled payment goes to interest (calculated on the current balance) and the rest goes to principal. When you send extra money tagged as principal, it skips the interest portion entirely — that dollar reduces next month's interest charge and every future month's.

The savings compound. Cutting the balance early in the loan, when interest charges are largest, has the biggest impact. That's why a $5,000 lump sum in year 1 saves more interest than the same $5,000 in year 20.

Thinking about a refi instead? Compare both strategies in our Should I refinance my mortgage? guide, or run the numbers on the main mortgage calculator.

Frequently asked questions

Does paying extra principal really save money?

Yes — and a lot of it. Every dollar of extra principal reduces the balance interest is charged against for every remaining month of the loan. On a 30-year mortgage at 6.5%, even an extra $200/month can save tens of thousands in interest and shave 5+ years off the payoff date.

Should I make extra payments or invest the money instead?

It depends on your mortgage rate vs your expected investment return. If your rate is ~7% and you can reasonably expect 8-10% in equities long-term, investing wins on paper. But mortgage prepayment is a guaranteed return equal to your rate — and it provides peace of mind. Many people do a mix: max retirement accounts first, then split surplus between investing and prepayment.

How should I tell my lender to apply the extra payment?

When you send extra money, write or note in the online portal that it should be applied to principal. Otherwise some servicers credit it as a prepayment of next month's payment, which doesn't save interest. Most lenders have a separate 'principal-only payment' field online.

Is there a prepayment penalty?

Most modern conventional and government-backed mortgages have no prepayment penalty. But some loans (especially older ARMs or non-QM loans) can. Check your loan documents under 'prepayment' or 'late charges' before making large extra payments.

Should I refinance or just pay extra?

If rates have dropped meaningfully, refinancing may save more than prepayment because it lowers every future interest charge. If rates are similar, prepayment is the simpler win. See our refinance calculator to compare.