Extra Mortgage Payment Calculator: Interest Saved and New Payoff Date
See how extra monthly, yearly or one-time payments pay your mortgage off early: interest saved, time saved, new payoff time, or the extra payment needed to be debt-free by a target year, with a yearly balance schedule and chart.
How it works
M = P × r ÷ (1 − (1 + r)^−n), r = annual rate ÷ 12 · each month: interest = balance × r; principal = M + extra − interest; balance −= principal, until the balance is 0 · interest saved = interest on the original schedule − interest with extra payments · extra needed for a goal of g months = M_goal − M, where M_goal = B × r ÷ (1 − (1 + r)^−g) and B is today’s balance
A fixed-rate mortgage payment is set so the loan reaches zero at the end of the term. Each month interest is charged on the remaining balance and the rest of the payment reduces principal. Any extra money goes entirely to principal, so it never collects interest again; the next month’s interest is lower, more of the regular payment goes to principal, and the effect compounds. That is why extra payments made early in the loan save the most. Choose “Savings from an extra payment” to add a monthly extra, and under More options a yearly extra (applied with every 12th payment) or a one-time lump sum; the calculator runs both schedules month by month and reports the interest saved, the time saved and the new payoff time. Choose “Extra needed for a payoff goal” to find the monthly extra that clears today’s balance in a chosen number of years. For a loan already in progress, enter the payments made so far: extras start with the next payment and the original loan amount, rate and term rebuild today’s balance. The required monthly payment never changes; you simply finish sooner. Results cover principal and interest only and assume the rate stays fixed.
Worked example
On a $300,000 loan at 6% for 30 years, the payment is $1,798.65 and interest over 360 payments totals $347,515. Paying $200 extra every month ($1,998.65 in total) clears the loan after 279 payments, 23 years 3 months, which is 6 years 9 months early, and cuts total interest to $256,341, saving $91,173 (26.2% of the original interest). The $55,600 of extra payments (the last payment is smaller) saves $1.64 of interest per extra dollar. To be mortgage-free in 20 years instead, the extra needed is $350.65 a month, which saves $131,686.
Sources: CFPB: What is a prepayment penalty? · CFPB: What is amortization? · Calculator.net: Mortgage payoff calculator (method comparison)
Frequently asked questions
Where should the extra payment go?
Tell your servicer to apply it to principal, not to prepay next month’s payment. Applied to principal, it permanently shrinks the balance that interest is charged on; otherwise it may sit as a credit or count as an early payment with no interest saved.
Is it better to pay extra or invest?
Compare your mortgage rate with what you could reliably earn elsewhere after tax. Paying down a 6% mortgage is a guaranteed 6% return; investing might earn more but carries risk. Many people keep an emergency fund and take any employer retirement match first, then split the rest.
Does an extra payment lower my monthly bill?
No. The required payment stays the same; you just finish sooner. To lower the required payment after a large lump sum, ask your lender about a recast, which re-amortizes the smaller balance over the remaining term for a small fee.
How much does $100 extra a month save?
On a $300,000, 30-year loan at 6%, $100 a month saves about $53,300 of interest and pays the loan off 3 years 11 months early; $200 a month saves about $91,000 and 6 years 9 months. Enter your own loan to see the exact figures.
Is one extra payment a year worth it?
Yes. Adding one extra monthly payment a year (for example $1,800 on the default loan, entered as a yearly extra) pays that 30-year loan off 5 years 3 months early and saves about $70,900. A biweekly plan does the same thing by paying half the payment every two weeks, which adds up to 13 payments a year.
Can my lender charge a fee for paying extra?
Some loans have a prepayment penalty, usually only if you pay off all or a large part of the loan in the first three to five years. Small extra principal payments normally do not trigger it, but check your loan documents or ask your servicer.
Related calculators
This is an educational estimate, not financial advice. Lenders use their own rounding, fees and terms — confirm exact figures with your lender or a licensed advisor.