Extra Mortgage Payment Calculator
One extra payment a month, applied to principal, can cut years off a mortgage. Enter your loan and the extra amount to see the saving.
How it works
Monthly payment: M = P × r × (1+r)n ÷ ((1+r)n − 1). The simulation then applies M plus your extra amount every month, with interest charged on the remaining balance, until the balance reaches zero.
Example: $300,000 at 6% over 30 years, plus $200 extra a month: payoff drops from 360 months to 279 months (23y 3m), and interest drops from $347,514.57 to $256,341.13 — $91,173.44 saved and 81 months early.
Frequently asked questions
Does the extra payment go to principal?
It must. Tell your lender (or tick the principal-only option) — if extra money is held as a future monthly payment, it does not cut interest.
What if I can only pay extra sometimes?
Irregular extra payments still help: every dollar of principal you repay early stops earning interest for the rest of the loan.
Biweekly or extra monthly — which is better?
They are close cousins. Biweekly equals about one extra monthly payment a year; a fixed extra monthly amount gives you exact control.
Is there a prepayment penalty?
Most modern US mortgages have none, but check your loan documents — a penalty would change the maths.