About the Extra Mortgage Payment Calculator
This extra mortgage payment calculator shows what happens when you pay more than the required amount. Enter your current balance, rate and remaining term, then add any combination of an extra amount every month, an extra payment once a year (for example from a bonus or tax refund) and a one-time lump sum in a month you choose.
The calculator runs your loan month by month twice — once as scheduled and once with the extra principal — and reports the interest you avoid, how many months come off the loan and your new payoff time. The chart shows the two balances side by side so you can see the gap widen over time.
It assumes a fixed-rate mortgage where extra money is applied directly to principal and the required payment stays the same, which is how most US mortgages handle prepayments. Check that your loan has no prepayment penalty and tell your servicer to apply extra funds to principal.
With the default inputs, the interest saved is $103,448.79. Change any value above to recalculate instantly.
How to use the extra mortgage payment calculator
- 1Enter your current balance, interest rate and years left on the loan.
- 2Add an extra monthly amount you could pay alongside each payment.
- 3Optionally add a once-a-year extra payment and a one-time lump sum with its month.
- 4Read the interest saved, payments eliminated and new payoff time.
- 5Ask your servicer to apply the extra money to principal, not future payments.
Formula and method
M is the required monthly payment from the standard amortization formula for your balance, rate and remaining term. Each month interest Iₖ is charged on the previous balance at r = annual rate ÷ 12; the payment M plus that month’s extra principal Eₖ (monthly extra, plus the yearly extra every 12th month, plus the lump sum in its month) reduces the balance.
The loan is simulated until the balance reaches zero, both with and without extras. Interest saved is the difference in total interest, and payments eliminated is the difference in the number of months. The final payment is reduced to exactly what is needed to clear the balance.
- M
- Required monthly principal and interest payment
- r
- Monthly rate (annual rate ÷ 12 ÷ 100)
- Eₖ
- Extra principal paid in month k
- Bₖ
- Balance after month k
Worked examples
$300,000 at 6.5%, 30 years, $200 extra a month
The required payment is $1,896.20. Adding $200 a month pays the loan off 83 months — 6 years 11 months — sooner and saves roughly $103,449 in interest, for $55,200 of extra principal paid.
$250,000 at 7%, 25 years left, $5,000 bonus each year
Putting a $5,000 bonus toward principal once a year on a $250,000 loan at 7% cuts 108 payments — nine years — and saves about $111,674 of interest.
$20,000 lump sum in month 1
A single $20,000 prepayment at the start of a $200,000, 6%, 30-year loan removes 81 payments (6 years 9 months) and saves about $77,442 in interest, because that $20,000 would otherwise accrue interest for decades.
Frequently asked questions
Is it worth making extra mortgage payments?+
Every extra dollar of principal earns a guaranteed return equal to your mortgage rate. It is usually worthwhile once you have an emergency fund, no high-interest debt and are capturing any employer retirement match.
Does an extra payment lower my monthly payment?+
Not on a standard mortgage. The required payment stays the same; the loan simply ends sooner. To lower the payment after a large prepayment, ask your lender about a mortgage recast.
Is one extra payment a year enough to make a difference?+
Yes. One extra monthly payment a year on a 30-year loan typically cuts around five to six years off the term at today’s rates and saves a large share of total interest.
Is it better to pay extra monthly or a lump sum?+
The earlier money reaches principal, the more interest it saves, so a lump sum today beats the same total spread over later months. Monthly extras are easier to budget and still save a lot over time.
Are there penalties for paying off a mortgage early?+
Most modern US mortgages have no prepayment penalty, and federal rules limit them on qualified mortgages. Check your note or Closing Disclosure for a prepayment penalty clause before paying ahead.
Results are estimates for educational purposes and are not financial advice. Rates, fees and terms vary — confirm with your lender or a licensed advisor before making decisions.