Build a full fixed-rate loan amortization schedule and see how extra principal can change interest cost and payoff time.
Mortgage payment formulas, amortization schedules, extra principal and worked loan-payment scenarios.
Enter the loan amount, annual interest rate, term and optional extra monthly principal. The result shows the scheduled payment, actual payment with extra principal, payoff time, total interest and a payment-by-payment schedule.
Each payment first covers interest on the outstanding balance; the remainder reduces principal. As the balance falls, the interest share generally decreases.
An extra monthly amount reduces principal faster. The calculator continues until the balance reaches zero and summarizes principal and interest by year.
For a home loan with extra-payment scenarios, use the mortgage payoff calculator. Also see how to calculate a mortgage payment, the loan payment calculator, and the home affordability calculator.
For a $250,000 loan at a fixed 6% annual rate over 30 years, the approximate monthly principal-and-interest payment is $1,498.88. First-month interest is $250,000 × (0.06 ÷ 12) = $1,250, leaving about $248.88 for principal. As the balance declines, interest generally falls and principal reduction rises.
Important: lender rounding may change individual schedule rows by pennies. Taxes, insurance, HOA charges, variable rates, and fees are not part of a basic principal-and-interest amortization calculation.
Yes. The results include the full monthly schedule plus an annual summary.
No. Check your lender’s payment instructions and loan terms.
See how formulas, sources and limitations are handled across ERICH Calculators.