See how extra monthly, yearly, or one-time payments reduce total interest and shorten your mortgage payoff timeline.
Extra payments change a mortgage balance before the scheduled final installment. Enter the outstanding balance, annual interest rate, remaining term, and any monthly, yearly, or one-time extra payment. The calculator compares the ordinary amortization path with the accelerated path, showing the change in total interest and payoff length. A frequent misunderstanding is that extra principal lowers the next required payment. Unless the lender recasts the mortgage, the usual effect is an earlier payoff while the scheduled principal-and-interest payment remains unchanged.
A concrete input and expected output from the current implementation.
Input
Loan balance: $1,000 Annual interest rate: 12% Remaining term: 1 year Extra monthly payment: $200 Yearly extra payment: $0 One-time extra payment: $0
Expected output
Scheduled payment: $88.85. No-extra payoff: 12 months with $66.19 total interest. With the $200 monthly extra: payoff in 4 months with $23.16 total interest. Time saved: 8 months. Interest saved: $43.03.
The monthly rate is 1%, so the first three accelerated payments are about $288.85 each. After those payments, $155.06 of principal remains; $1.55 of final-month interest produces a $156.61 last payment, making total interest $23.16.
The baseline schedule treats the entered annual rate as constant and finds the level principal-and-interest payment that amortizes the balance over the remaining term. For each monthly period, interest is calculated on the unpaid balance and the rest of the payment reduces principal. The accelerated schedule adds the selected extra principal before continuing that calculation.
Monthly, yearly, and one-time additions are not interchangeable because timing controls how long principal remains outstanding. A monthly extra affects every later interest calculation; an annual or single payment changes the balance only after its assumed payment date. The results compare total interest and payoff length with the no-extra schedule, and the last payment is limited to the amount still owed.
Usually no. In this calculation, the scheduled principal-and-interest payment stays the same while the balance reaches zero sooner. A lender may offer a mortgage recast after a substantial principal reduction, and refinancing can create a new payment, but neither outcome follows automatically from the extra-payment schedule shown here.
Only as a scenario that assumes the entered rate remains unchanged. It is not a reliable full-term forecast when future rate resets alter the required payment and interest accrual. Separate runs can test possible rates, but no single run predicts unknown resets; consult the mortgage terms for the actual adjustment schedule.
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