United States · Home loans
Extra mortgage payment calculator.
Enter your current balance, rate and remaining term, then add a monthly extra payment or a one-time lump sum to see the interest and months you save.
Extra payments go straight to principal, so every later month charges interest on a smaller balance. The earlier in the loan you pay, the more interest you avoid.
Your loan
What you save
How the calculation works
The tool first derives your required monthly principal-and-interest payment from the balance, rate and remaining term. It then steps through the loan one month at a time: interest for the month is the balance times the rate divided by 12, the rest of the payment (plus any extra) reduces principal, and the loop ends when the balance reaches zero. It runs the schedule twice, with and without your extra payments, and reports the difference in interest and in months. A lump sum is applied to the balance at month zero.
Worked example
A $300,000 balance at 6.5% with 28 years left has a required payment of $1,941.05 and will cost $352,192 in interest over 28 years. Adding $200 a month cuts the payoff to 22 years and the interest to $263,934, saving $88,258 and 6 years. A single $20,000 lump sum today with no monthly extra saves $85,903 and 4 years 6 months, which is why the same dollars are worth more early than late.
Before you send extra money
- Tell the servicer it is principal. Many servicers apply an unlabeled overpayment to the next month's payment instead. Use the "additional principal" field on the payment page or a separate check and confirm it on the next statement.
- Check for a prepayment penalty. Most modern qualified mortgages cannot carry one, but some loans do in the first years; your note and closing disclosure say.
- Compare with other uses of the cash. Paying down a 6.5% mortgage is a guaranteed 6.5% return before the interest deduction. Compare that with employer 401(k) match (usually better), paying off higher-rate debt and holding an emergency fund.
- Biweekly plans. Half a payment every two weeks makes 26 half-payments, equal to 13 full payments a year, which is roughly one extra payment annually. Enter one-twelfth of a monthly payment as the extra to approximate it.
- The interest deduction. If you itemize, mortgage interest may be deductible (IRS Topic 505), which slightly lowers the real return on extra payments. Most households now take the standard deduction.
What this tool does not cover
Escrow, PMI (extra principal can help PMI end sooner), adjustable-rate resets, interest-only periods, and servicers that round or apply payments on different dates. Use the numbers as a planning estimate and confirm payoff figures with your servicer.
Common mix-ups
Assuming an extra payment lowers the monthly bill (it shortens the loan; only a recast lowers the payment); sending extra money without marking it as principal; and entering the original term instead of the years remaining on your latest statement.
Frequently asked questions
How much interest will extra payments save?
It depends on the balance, rate and timing. The calculator shows it exactly for your inputs; in the default example, $200 a month saves about $88,000 of interest and six years.
Is it better to pay extra monthly or in one lump sum?
Dollar for dollar, an earlier payment saves more interest because it removes balance for longer. A lump sum now beats the same total spread over later months, but regular extras are easier to sustain.
Do extra payments lower my monthly payment?
No. They shorten the loan unless you ask for a recast, which re-computes the payment on the lower balance. See the recast calculator.
Will extra payments remove PMI sooner?
Yes. PMI can be cancelled at 80% of the original value and ends automatically at 78% of the scheduled balance, so extra principal can help you reach the request point sooner.
Does my lender charge a penalty for paying early?
Most conventional loans do not, but check your note and closing disclosure for a prepayment penalty clause.
Sources
- CFPB, What is an escrow or impound account? — how taxes and insurance are collected with the mortgage payment (retrieved 2026-11)
- CFPB, When can I remove PMI from my loan? — request at 80%, automatic termination at 78% (retrieved 2026-11)
- IRS Tax Topic 505, Interest expense — when mortgage interest and points are deductible (retrieved 2026-11)
Last updated November 8, 2026. Tax-law figures are for tax year 2026.
Estimate only
This is an educational calculation, not tax, legal or investment advice. Your plan, lender, employer or tax professional has the final numbers.