Calculate how extra payments accelerate mortgage payoff and save interest. Free online mortgage payoff calculator.
Making extra payments toward your mortgage principal is one of the most effective ways to save money on interest and become debt-free faster. Even small additional amounts can have a dramatic impact because they directly reduce the principal balance, which in turn reduces the interest charged in every subsequent month.
How it works: When you make your regular mortgage payment, the interest portion is calculated based on your remaining balance. Any extra payment goes directly toward reducing the principal. Because interest is calculated on a smaller balance the next month, more of your regular payment goes toward principal, creating a compounding effect that accelerates payoff.
The formula: Each month, Interest = Remaining Balance × (Annual Rate ÷ 12). The remainder of your payment (regular + extra) goes to principal. By recalculating this each month with a reduced balance, the calculator determines your new payoff date and total interest savings.
Common strategies: The most popular approach is adding a fixed amount each month (e.g., $100-500 extra). Another strategy is making one extra payment per year (dividing your monthly payment by 12 and adding it to each payment). Bi-weekly payments (half your monthly payment every two weeks) effectively create 13 full payments per year instead of 12.
That $200 extra per month saves you over $39,000 in interest and pays off your home years earlier. Try different amounts to see the impact.
Cross-checked against authoritative formulas (IRS, NIST, ACM) and updated for 2025/2026 tax years and rates.
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A mortgage payoff calculator is a free tool that shows how extra payments shorten your mortgage term and reduce total interest. Our mortgage payoff calculator accepts any one-time or recurring extra payment, and shows the new payoff date, interest savings, and shortened term. The mortgage payoff calculator helps homeowners decide whether to pay extra or invest.
How it works
Our mortgage payoff calculator lets you find your new payoff date and total interest saved by adding extra principal to your mortgage, in four steps.
Type your current loan balance, the interest rate, and the original loan term. Your monthly statement has all three values.
Type what you currently pay each month. The calculator uses this as the baseline and adds your extra payment on top.
Type how much extra you want to add each month, or the one-time lump sum you can apply to principal now.
The result shows the new payoff date, the months saved off your original schedule, and the total interest you save. A small extra payment can shave years and tens of thousands of dollars.