Extra Mortgage Payment Calculator
See how a small extra payment each month — or one well-timed lump sum — can save tens of thousands in interest and cut years off your mortgage.
Why extra payments work
Every extra dollar you put toward your mortgage today is a dollar you don't pay interest on for the rest of the loan. On a 30-year mortgage at 7%, every $1 of principal you pay down in the first year saves roughly $5-6 in interest over the life of the loan.
The biweekly trick
Switching from monthly to biweekly payments is one of the easiest ways to accelerate payoff without feeling the pinch. You pay half your normal monthly payment every two weeks. Because there are 52 weeks in a year, you make 26 half-payments — equivalent to 13 monthly payments instead of the normal 12.
That single "hidden" 13th payment, applied entirely to principal, cuts roughly 4-6 years off a typical 30-year mortgage at current rates.
Lump sums: timing matters
A $10,000 lump sum applied in year 1 of a 30-year mortgage at 7% saves roughly $40,000 in interest. The same $10,000 applied in year 20 saves only about $4,000. Apply lump sums as early as possible.
How to actually do it
Most lenders accept extra payments without issue, but you must specify they apply to principal, not the next month's payment. Some servicers require a separate "principal-only" option in their portal or a written instruction. Always confirm in writing.
Set up the extra as an automatic recurring transfer if you can — that's how it actually gets done over decades.
Disclaimer: This calculator provides estimates only. Confirm with your lender that extra payments apply to principal. Some loans carry prepayment penalties (typically only in the first 3-5 years of non-conforming loans). This is not financial advice.