Extra Payment Calculator

Last updated July 2, 2026

Making extra payments on any amortizing loan — mortgage, auto, student loan, or personal loan — produces a compounding benefit that accelerates dramatically as more time remains on the loan. The core mechanism is simple: every extra dollar reduces the principal on which future interest is calculated, permanently lowering interest charges for every remaining payment period. On a 30-year mortgage, an extra $100 per month from the first payment forward typically shortens the loan by four to six years and saves $25,000 to $50,000 in interest depending on the original balance and rate. The same $100 per month added in year 20 of the same mortgage shortens it by perhaps 8 to 10 months — meaningful but far less powerful, because the time for compounding savings to accumulate has shortened.

The practical question extra payment calculators answer is where to direct available cash beyond required monthly minimums. When someone has multiple debts and an extra $300 to allocate, the question is whether that $300 saves more interest on the mortgage, the car loan, or the credit card. The answer almost always favors the highest-rate debt first — the credit card at 22 percent saves $22 per year in interest for every extra $100 applied, while the mortgage at 6.5 percent saves $6.50. At that rate differential, directing extra payments to the credit card is 3.4 times more cost-effective than the mortgage, regardless of the balances involved.

The calculation shows the interest saved from directing your available extra payment to each of your debts separately. The debt with the highest interest rate almost always produces the greatest savings per extra dollar — this is the core logic of the avalanche method applied to extra payments. Use the calculator to confirm the ranking and to see the concrete months and dollars saved from the amount you're actually able to commit.