How a mortgage payoff is calculated
A mortgage is a fully amortizing loan: every payment covers one month of interest on the balance you still owe, and whatever is left over reduces the principal. Because interest is charged on the remaining balance, the split shifts over time — early payments are mostly interest, later payments are mostly principal.
This calculator solves that schedule month by month. Give it your current balance, your annual interest rate and how many years are left, and it works out the level payment that clears the loan exactly on schedule, then reports the payoff date and the total interest you will pay to get there.
If you already know your payment and want the timeline instead, switch to payment mode. The math is the same equation solved for months rather than for dollars.
Why extra principal payments work so hard on a mortgage
Extra money applied to principal permanently removes that dollar from every future interest calculation. On a 30-year loan at a typical rate, a dollar of extra principal in year one can save two dollars or more of interest over the life of the loan — which is why a modest, consistent extra payment often cuts years off the term.
Timing matters more than size. The same extra payment made in year two saves far more than one made in year twenty, because it has more remaining months to compound against.
When you send extra money, tell your servicer in writing to apply it to principal. Otherwise many lenders bank it as a prepaid future installment, which does not shorten the loan at all.
What the result does not include
Payoff figures here cover principal and interest only. Your actual monthly payment likely also includes escrow for property taxes, homeowners insurance and, if you put down less than twenty percent, private mortgage insurance. Those costs do not shrink when you prepay principal, though PMI usually drops off once you cross twenty percent equity.
Also check your note for a prepayment penalty. They are uncommon on conforming loans today, but they still exist on some non-qualified and older mortgages.
Common mistakes
Entering the original loan amount instead of the current balance is the most common one — use the balance from your latest statement. Second is using the term you started with rather than the years remaining. Third is entering the full escrowed payment in payment mode; use only the principal-and-interest portion, which your statement breaks out.