Payoff Ruler

Mortgage extra payment calculator

Your base payment, your total payment, and exactly what extra principal buys you.

Enter your loan, add whatever extra you can send each month, and see your required payment, your new payoff date, and your total interest saved — all in one place.

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Your loan

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Standard monthly payment (P&I)

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Total monthly payment (base + extra)

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Payoff date

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Interest saved · time saved

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Timeline

Year 0 Year 30
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Balance over time

How base monthly mortgage payments & extra principal payments work

Your standard monthly payment — principal and interest, or "P&I" — is fixed for the life of a fixed-rate loan. It's calculated from three numbers: your loan amount (home price minus down payment), your monthly interest rate (annual rate ÷ 12), and your total number of payments (term in years × 12). The formula spreads the loan into equal payments where, early on, most of each payment covers interest, and over time more of it covers principal — even though the payment itself never changes.

M = P × [r(1+r)^n] / [(1+r)^n − 1]
P = loan principal  ·  r = monthly interest rate  ·  n = total number of payments

Your total monthly payment in this calculator is simply that base P&I figure plus whatever extra you choose to send. The extra amount is applied entirely to principal, which lowers the balance interest is calculated on for every remaining month — shortening the loan and reducing total interest paid, without changing the required base payment itself.

A sample scenario

A $350,000 home with 20% down and a 30-year loan at 6.5% gives a $280,000 mortgage with a base payment of roughly $1,770/month and about $357,000 in total interest over the full term. Adding $200/month extra brings the total monthly payment to about $1,970, cuts the payoff to roughly 22 years 8 months, and saves an estimated $101,000 in interest. These are the calculator's default values — change them to match your own loan.

Frequently asked questions

How is my base monthly mortgage payment calculated? +
Your base principal-and-interest payment is calculated from your loan amount (home price minus down payment), your monthly interest rate, and the total number of payments in your term. The formula spreads the loan into equal payments where the interest portion shrinks and the principal portion grows every month, so the total payment stays level from your first month to your last.
Do extra mortgage payments always go toward the principal? +
Only if your lender applies them that way. Most lenders default extra payments to principal reduction, but some apply them to your next due date instead. Always confirm with your servicer or note "apply to principal" when you pay.
Will extra payments lower my required monthly payment? +
No. A standard fixed-rate mortgage keeps the same required base payment for the full term. Extra payments shorten the loan term and reduce total interest instead of lowering the bill you owe each month, unless you specifically request re-amortization from your lender.
Is it better to pay extra monthly or make one lump sum payment a year? +
Paying extra every month saves slightly more interest than a single annual lump sum of the same total amount, since the principal is reduced sooner and interest accrues on a lower balance for more of the year. The gap is usually small, so consistency matters more than exact timing.
Is there a penalty for paying off my mortgage early? +
Most conventional U.S. mortgages originated after 2014 don't carry prepayment penalties, but some loans — older, non-QM, or investment-property loans — do. Check your note or ask your servicer before making large extra payments.