Use this mortgage payoff calculator to see how extra principal payments (monthly, yearly, and lump sums) can move up your payoff date and reduce the interest you pay from today forward.
Advanced options
| Monthly extra tested | Payoff date | Interest saved |
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| Date | Interest | Principal | Extra | Balance |
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How to use this calculator
- Pick What do you know? to match the numbers you have from your mortgage statement.
- Enter your current principal balance (principal means the amount you still owe).
- Enter your interest rate (interest is the fee you pay for borrowing money), as a percent per year.
- Enter your monthly payment for principal + interest only (do not include escrow for taxes/insurance).
- Enter payments remaining (how many monthly payments are left if you make only the normal payment).
- Set your extra principal plan: extra each month, extra each year, and/or a one-time lump sum. Extra principal means money that goes to the balance, not to interest.
- Open Advanced options if you want to choose when extra payments start, which month your yearly extra happens, or schedule up to 3 lump sums by month.
- Click Calculate. Read the payoff dates, time saved, interest saved, and the estimated final payment amount.
- Use the amortization preview to sanity-check a few early payments and the last payments without scrolling a full schedule.
- Use the sensitivity line to see how interest saved changes at extra $50, $100, or $200 per month (and enable biweekly comparison only if you truly will make 26 half-payments per year).
Methodology
What this calculator models
This models the remaining payoff of a fixed-rate mortgage from today forward using an amortization schedule (an amortization schedule is a month-by-month payoff plan that shows how much of each payment goes to interest vs principal) [1]. It compares (1) your normal plan with no extra principal to (2) your plan with extra principal payments.
Inputs and key definitions
Principal is the remaining loan balance you still owe. Interest is the cost of borrowing, charged on the remaining balance each period [4]. The annual interest rate is converted to a monthly rate by dividing by 12.
Step 1: Convert annual rate to a monthly rate
Monthly interest rate = (annual rate / 100) / 12.
Step 2: Simulate the loan month by month (baseline and with extra)
For each month, the calculator computes: interest for the month = current balance times the monthly rate. Then scheduled principal = scheduled payment minus that interest. If scheduled principal is zero or negative, the payment does not cover the interest and the loan cannot amortize; the calculator stops and asks you to increase the payment or check the rate/balance.
Step 3: Apply extra principal payments
Extra principal for a month can include: (a) extra monthly amount (if the month is on or after your chosen start month), (b) extra annual amount in the chosen annual-extra month each year (on or after the start month), and (c) up to three optional lump sums applied in their chosen months. Extra payments are treated as principal-only, meaning they directly reduce the balance and therefore reduce future interest [3].
Step 4: Last payment handling (no negative balance)
If the scheduled payment plus that month’s extra principal is more than what is needed to finish the loan, the calculator caps the final payment at exactly: remaining balance plus that month’s interest. This is why the estimated final payment is often smaller than your normal payment.
Totals and comparisons
Total interest remaining is the sum of all monthly interest amounts from now until the balance reaches zero. Interest saved equals baseline interest remaining minus interest remaining with your extra-payment plan. Time saved is the difference between the two payoff dates.
Rounding
You can choose a rounding method because lenders may round interest and principal to cents each payment. Different rounding can cause small differences versus your statement.
Biweekly comparison (optional)
If you enable biweekly comparison, the calculator estimates payoff using 26 half-payments per year (often described as making 13 full payments per year) [2]. This is an estimate because real servicers may credit payments on different dates, which can slightly change interest.
Important note
Some mortgages have prepayment penalties (a fee for paying off early) [5]. This calculator shows interest savings, but it does not include any penalty fees or taxes.