Mortgage Payoff Calculator

How to use this calculator

1. Enter or choose remaining balance.
2. Enter or choose interest rate (per year).
3. Enter or choose time left: years.
4. Enter or choose time left: extra months.
5. Enter or choose extra payment each month.
6. The interest saved updates as you type. Use Copy result or Share to keep it.

Method

Regular payment P = B·i(1+i)^n ÷ ((1+i)^n − 1); months to pay off with extra E: N = −ln(1 − B·i ÷ (P + E)) ÷ ln(1 + i), rounded up; Interest saved = interest on current plan − interest with extra payments

B

remaining balance (after any lump sum for the new plan)

i

monthly rate = annual rate ÷ 12

n

months left on the current plan

E

extra monthly payment

Worked example

1. Regular payment on 200,000 at 0.5% a month over 360 months = $1,199.10; interest over the term = 1,199.101 × 360 − 200,000 = $231,676.38.
2. Paying 1,399.10: N = −ln(1 − 200,000 × 0.005 ÷ 1,399.10) ÷ ln(1.005) = 251.5, so 252 payments (21 years).
3. Interest falls to $151,875.87, a saving of $79,800.51 and 108 months.

Adding $200 a month to a $200,000, 6%, 30-year mortgage pays it off 9 years early and saves about $79,800 in interest.

What the result means

Extra payments save the most when made early, because they remove balance that would otherwise accrue interest for decades. Compare the saving with what the money could earn elsewhere, and keep an emergency fund first.

Assumptions and limits

• The interest rate is fixed and interest is charged monthly on the outstanding balance.
• The regular payment is the one that clears the balance over the time left; taxes and insurance are excluded.
• All extra money reduces the principal immediately.
• Some lenders charge early repayment fees or limit overpayments; check your mortgage terms.
• Adjustable-rate mortgages need a different calculation.