Mortgage Payoff Calculator
Find out exactly how many years — and how many thousands of dollars in interest — extra monthly payments cut from your mortgage.
Why extra payments punch above their weight
Mortgage interest is charged every month on your remaining balance. An extra payment goes 100% to principal, so it doesn't just save one month of interest — it removes that slice of balance from every future month's interest charge. The math compounds in your favor:
This calculator simulates your loan month by month, once with your current payment and once with the extra amount, then compares total interest and payoff dates.
Balance $300,000, rate 6.5%, payment $1,896/mo (a fresh 30-year loan):
Adding $200/mo pays the loan off in about 24 years instead of 30 — roughly 6 years sooner — and saves approximately $71,000 in interest.
Total extra paid in: about $58,000. Interest saved: about $71,000. That's the power of principal reduction.
Ways to make extra payments
| Strategy | How it works | Typical effect (30-yr loan) |
|---|---|---|
| Round up | e.g., pay $2,000 instead of $1,896 | 1–2 years sooner |
| Fixed extra monthly | Add a set amount every month | $100/mo ≈ 3–4 yrs sooner |
| Biweekly payments | Half-payment every 2 weeks = 13 full payments/yr | 4–6 years sooner |
| Annual lump sum | Tax refund or bonus to principal | Varies with amount |
Before you prepay: three checks
First, confirm your loan has no prepayment penalty (rare today, but check). Second, tell your servicer extra amounts are principal-only — otherwise they may be applied as an early next-month payment, which saves you nothing. Third, make sure the money isn't needed elsewhere: high-interest debt (see the credit card payoff calculator) and an emergency fund should come first, since mortgage prepayments are hard to get back out of the house.
Frequently asked questions
Do extra mortgage payments really save money?
Yes — every extra dollar permanently reduces the balance all future interest is charged on. On a $300,000 balance at 6.5%, an extra $200/mo saves about $71,000 in interest and roughly 6 years of payments.
Is it better to pay extra monthly or as one lump sum?
Sooner is mathematically better — a lump sum today beats the same total spread over a year. But consistent monthly extras are easier to sustain and nearly as effective.
Should I pay off my mortgage early or invest instead?
Extra payments earn a guaranteed return equal to your rate. Compare that to what you realistically expect from investing (try the investment calculator), and consider doing some of both.
Do I need to tell my lender the extra money is for principal?
Yes — mark it "principal-only." Some servicers otherwise apply extras to next month's payment, which eliminates the benefit.
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Note: Results are estimates from a month-by-month simulation assuming a fixed rate and consistent payments; actual servicer calculations may differ slightly. Not financial advice. Last reviewed: July 2026.