Mortgage Amortization Calculator

A mortgage amortization calculator shows how each mortgage payment is split between principal and interest and how fast the loan balance falls over time. It also helps you test extra payments, estimate total interest, and see whether paying ahead could shorten your payoff date and save money.

A mortgage amortization calculator maps out how a home loan is repaid through scheduled monthly payments. For a fixed-rate mortgage, the principal-and-interest payment usually stays constant, but the makeup of that payment changes every month. Early in the loan, a larger share goes to interest because the outstanding balance is highest. Later, more of each payment goes to principal, which accelerates balance reduction.

That schedule matters in real life because borrowers often want more than a simple monthly payment estimate. They want to know how much interest they will pay over 15, 20, or 30 years, how quickly they will build equity, and what happens if they add extra principal. A mortgage amortization calculator answers those questions by showing the payoff timeline and the remaining balance after each payment period.

Buyers use this type of tool before closing to compare loan terms, while homeowners use it during budgeting, refinancing analysis, and early payoff planning. Investors also review amortization when modeling cash flow and equity growth. Because interest is front-loaded on most mortgages, even modest extra payments made early can have a meaningful effect on lifetime borrowing cost. That is why a mortgage amortization calculator is useful not just for estimating payment mechanics, but for making better financing decisions.

1. Enter the loan amount, annual interest rate, and mortgage term in years.
2. Add a start date if you want an estimated payoff month and year.
3. Enter an optional extra monthly payment to see how recurring prepayments change the schedule.
4. Add an optional one-time extra payment and the month when you plan to make it.
5. Click Calculate to update the payment summary, payoff timing, interest totals, and yearly amortization table.
6. Adjust one variable at a time to compare standard payoff versus accelerated payoff scenarios.

Mortgage amortization uses the standard fixed-loan payment formula:

M = P x [r(1+r)^n] / [(1+r)^n - 1]

• M: monthly principal-and-interest payment.
• P: original loan principal.
• r: monthly interest rate, equal to APR divided by 12.
• n: total number of monthly payments.

Monthly Payment

The monthly principal-and-interest amount required to amortize the loan based on your current inputs. This is the baseline payment before any optional extra principal.

Payoff Time

This shows how long the mortgage lasts under the selected payment strategy. If you add extra principal, the payoff period should shorten.

Total Interest Paid

This is the cumulative interest cost across the full amortization schedule. It helps show the long-term price of borrowing.

Interest Savings

This compares the accelerated schedule against the standard schedule and measures how much interest extra payments can eliminate.

End Balance by Year

The table tracks the remaining loan balance after each year, which is useful for estimating equity growth and refinance timing.

Assume a $400,000 mortgage, a 6.25% fixed interest rate, a 30-year term, an extra monthly payment of $200, and a one-time extra payment of $5,000 in month 12.

First, the standard amortization formula produces a principal-and-interest payment of about $2,462 per month. Without any extra payments, the loan runs for the full 360 months and generates substantial lifetime interest. Next, add the recurring $200 extra payment and the $5,000 one-time prepayment after the first year. Both amounts go directly toward principal, which reduces the balance faster than the standard schedule.

Final result: the payoff period drops to roughly 25 years 10 months, and total interest falls by tens of thousands of dollars compared with the original 30-year plan. The outcome shows why early principal reduction matters. Lower balance today means less interest accrues in future months, so the savings compound over the life of the loan.