Mortgage Extra Payment Calculator
See how making extra mortgage payments shortens your loan and slashes total interest. Compare monthly extra, yearly lump sum, or one-time prepayment scenarios.
What is Mortgage Extra Payment Calculator?
The mortgage extra payment calculator shows what happens when you pay more than the minimum monthly payment. Even small extras compound into massive interest savings over a 30-year loan.
Try a $200 monthly extra on a typical 30-year fixed mortgage and you'll often shave 6-8 years off the loan and save tens of thousands in interest.
Formula
The standard amortization formula computes the base monthly principal & interest payment M = P × r × (1+r)N ÷ ((1+r)N − 1). Extra payments are then applied directly to principal each month, accelerating payoff. Each month: interest = balance × monthly_rate, principal = base_payment − interest + extra. The simulation runs month-by-month until the balance hits zero.
Worked example
$320,000 mortgage at 6.75% APR for 30 years. Base payment: $2,076. Original total interest: $427,346.
Add $200/month extra. New payoff: 23 years 4 months. Months saved: 80. Interest saved: $127,840.
How to use this calculator
- Enter your loan amount, rate, and term.
- Add any combination of monthly extra, yearly lump sum, or one-time prepayment.
- The calculator shows new payoff time, months saved, and interest saved.
Extras don't replace your minimum payment — they add to it. Verify with your lender that extra payments are applied to principal (not future interest).
Frequently asked questions
Is paying extra on my mortgage always smart?
Compare to other returns. If your mortgage is 6.75% and you can earn 7% in a high-yield savings or 9-10% historical S&P 500, the math may favor investing instead. Tax-deductible mortgage interest can shift this further. Generally: pay off high-interest debt first, max your 401k match, build emergency fund, then consider extra mortgage payments.
Will extra payments lower my monthly payment?
No — they shorten the loan term but the monthly payment stays the same. To lower the monthly payment, you need to refinance the loan.
What about biweekly payments?
Paying half your monthly payment every two weeks results in 26 half-payments per year = 13 full monthly payments instead of 12. That's effectively one extra monthly payment per year. Use the "extra yearly lump sum" field set to one monthly payment to model this.
Should I tell my lender it's a principal payment?
Yes. Some lenders by default apply extra payments to next month's payment (interest first), which doesn't accelerate payoff. Specify "apply to principal" in writing. Most online portals have a checkbox.
Is there a prepayment penalty?
Most modern fixed-rate U.S. mortgages have no prepayment penalty, but some adjustable-rate or subprime loans do. Check your loan documents before making large extra payments.