Extra Mortgage Payment Calculator

This extra mortgage payment calculator shows what happens when you pay more than your required payment. Add a monthly extra amount, a one-time lump sum, or both. You see how much total interest you save, how many months sooner the loan ends, and your total interest with and without the extra money.

How to use this calculator

Start with your loan’s basic details, then test different extra amounts.

• Loan amount, rate and term. For a brand-new loan, enter the original amount and full term. For a loan you have had for years, enter today’s balance and pick the term closest to the years you have left.
• Extra principal each month. Even small amounts help. Try $50, $100 and $200 to compare.
• Lump sum and month. Use this for a bonus, tax refund or inheritance. Month 12 means the lump sum is paid with your 12th payment.

How it is calculated

The tool builds two month-by-month schedules and compares them.

1. Regular payment M = P × r(1+r)^n / ((1+r)^n − 1), with r as the monthly rate and n as the number of payments.
2. Each month, interest = balance × r.
3. Principal paid = M − interest + extra (+ lump sum in the chosen month).
4. The balance falls by the principal paid, until it reaches zero.
5. Interest saved = total interest on the regular schedule − total interest on the faster schedule.
6. Months saved = regular number of payments − new number of payments.

Assumptions: a fixed rate, every extra dollar applied to principal, no prepayment penalty, and no change to the required payment. Taxes, insurance and mortgage insurance are not included.

Worked example

The same loan with different extra payments:

What your result means

Your result shows the guaranteed savings of prepaying at your mortgage rate. The earlier in the loan you pay extra, the larger the effect, because early balances are highest. The CFPB notes that even an extra $100 a month could shorten a loan by several years.

Rules that change the answer:

• How your servicer applies the money. The CFPB advises checking whether your loan allows extra payments and making sure they go to principal rather than interest.
• Prepayment penalties. The CFPB says penalties apply only if you agreed to one at closing, usually when you pay off the whole loan within three or five years. Small extra principal payments usually don’t trigger them.
• PMI. If extra payments bring your balance to 80% of your home’s original value sooner, the CFPB says you can ask to cancel PMI early. For example, on a $380,000 loan on a $400,000 home at an example 6.5%, $200 a month extra moves the 80% point from about month 124 to about month 87.
• Refinancing. Freddie Mac notes you can put savings from a lower payment toward principal to pay off a loan sooner.

Common mistakes

• Sending extra money without marking it as principal, so it may be treated as an early payment instead of lowering your balance.
• Prepaying the mortgage before building an emergency fund.
• Paying extra on a low-rate mortgage while carrying high-rate credit card debt.
• Expecting your required payment to drop. Usually the loan just ends sooner.
• Forgetting to check for a prepayment penalty before a large lump sum.

Related guides and tools

Read when you can remove PMI to use prepayments to drop mortgage insurance, when to refinance your mortgage to compare prepaying with refinancing, and how much house you can afford to keep room in your budget.

Then view the full payoff path in the amortization schedule calculator, find your PMI dates with the PMI removal calculator, or compare a shorter loan with the 15 vs 30 year mortgage calculator.