Mortgage Payoff Calculator with Extra Payments
See how extra monthly or one-time payments cut years off your mortgage and slash total interest, with a full side-by-side amortization comparison.
How this mortgage payoff calculator works
A mortgage is an amortizing loan: each fixed monthly payment is split between interest on the current balance and principal that reduces it. In the early years most of every payment goes to interest, which is why a 30-year loan can cost more in interest than the home itself. This calculator shows how adding extra principal changes that picture.
The math is simple. Any amount you pay above the scheduled payment is applied entirely to principal, permanently lowering the balance that interest is charged on. A smaller balance accrues less interest every month thereafter, so the loan amortizes faster and the total interest falls. Enter a recurring monthly extra, a one-time lump sum, or both, and the tool rebuilds the full amortization schedule month by month — trimming the final payment so the balance lands exactly on zero.
A worked example: on a $300,000 loan at 6.5% over 30 years, the payment is about $1,896. Paying an extra $200 each month directs that money straight to principal and pays the loan off years early, cutting tens of thousands in interest. Run your own numbers above to see the exact payoff date, interest saved, and a side-by-side comparison of the two schedules.
How to read the result: the headline figures are the time and interest you save versus the original schedule. The earlier in the loan you add extra principal, the larger the saving, because more of your regular payment still goes to interest at the start. Before committing, make sure your servicer applies extra payments to principal and check your loan for any prepayment penalty. Whether prepaying beats investing the same money depends on your mortgage rate, expected investment return, and risk tolerance — this is educational, not individualized advice.