Extra Mortgage Payment Calculator

How to use the extra mortgage payment calculator

Use this calculator to estimate how much interest you could save by adding extra principal to your mortgage payment. Enter your current loan balance, interest rate, remaining term, and the extra amount you want to pay each month. You can also enter a one-time principal payment if you are planning to use a bonus, tax refund, inheritance, or home-sale proceeds.

The result shows the regular principal-and-interest payment, the new payment after the extra monthly amount, estimated interest saved, and estimated payoff time. The calculation focuses on the loan balance and interest. It does not include property taxes, homeowners insurance, escrow changes, HOA dues, or lender-specific fees. For a full monthly housing estimate, use the mortgage calculator. For a month-by-month payoff table, use the amortization schedule calculator.

The Consumer Financial Protection Bureau, 2026 mortgage resources explain that maintaining a mortgage starts with understanding the monthly mortgage statement and payment process. This calculator is an educational estimate, not legal, tax, or financial advice. Your lender or servicer controls how payments are accepted and posted.

Why extra payments change the math

A fixed-rate mortgage payment is designed so one payment amount pays the loan down to zero over a fixed term, such as 15, 20, or 30 years. Each month, interest is calculated on the remaining balance. The rest of the payment reduces principal. Early in the schedule, the balance is high, so the interest portion is large. Later in the schedule, the balance is smaller, so more of each payment goes to principal.

An extra principal payment changes that pattern. When you reduce the balance earlier, every future month starts from a smaller balance. That is why a modest recurring amount can have an outsized effect. In the default example, a $320,000 mortgage at 6.5% for 30 years has a regular principal-and-interest payment of about $2,022.62. Adding $250 per month raises the cash payment to $2,272.62, but it cuts the payoff estimate from 360 months to 267 months and saves about $122,992.85 in interest.

The timing matters. A $250 extra payment in month 1 avoids interest for almost the entire remaining term. The same $250 paid near the end of the loan still helps, but there are fewer future interest charges left to avoid. This is why lump sums made early can be especially effective.

Common extra payment strategies

One approach is to round up the payment. If your mortgage payment is $2,022.62, you might pay $2,100 or $2,250. This is simple, repeatable, and easy to automate if your servicer supports principal-only instructions.

A second approach is to divide one extra monthly payment by 12 and add that amount each month. If your regular payment is $2,400, adding $200 per month has roughly the same annual principal effect as one extra payment per year. A biweekly mortgage payment calculator models a similar idea using 26 half-payments per year.

A third approach is to use occasional windfalls. A $10,000 principal payment on a $300,000 mortgage at 5% can save about $32,366.35 in interest in this calculator’s model. This works because the balance drops immediately, and the future amortization schedule runs from that lower balance.

When extra mortgage payments may not be the best first move

Extra mortgage payments are not automatically the best use of every dollar. If you have high-interest credit card debt, no emergency fund, or an employer retirement match you are not capturing, those may deserve priority. The guaranteed return from extra principal is roughly the mortgage rate you avoid, but your household liquidity and risk matter too.

Also check whether your loan has any prepayment restrictions. Most modern U.S. residential mortgages do not penalize ordinary extra principal payments, but assumptions are expensive here. Confirm the rule in your note or with your servicer. Also confirm that the payment is applied to principal, not held as a future scheduled payment.

Extra payments versus refinancing

Extra payments and refinancing often get compared because both can reduce interest. They work differently. Extra payments keep your current loan intact and reduce the balance faster. Refinancing replaces the loan, possibly with a lower rate, shorter term, or different payment. Refinancing may also add closing costs and can restart the amortization clock if you choose a new long term. If you are considering that path, compare this tool with the refinance calculator before making a decision.

For planning, use this calculator as a first pass. Then compare the result with your full budget, emergency savings, and other debt costs. A great mortgage payoff plan is one you can sustain without creating cash-flow stress elsewhere.