Amortization Calculator
Generate a full loan amortization schedule showing principal, interest, and balance for every payment, with optional extra payments.
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About the Amortization Calculator
An amortization schedule is the detailed, payment-by-payment breakdown of exactly how a loan is repaid: how much of each payment is interest, how much is principal, and what the remaining balance is afterward. This calculator generates that schedule for any fixed loan, and lets you add an extra monthly payment to see how much faster the loan is paid off.
How It Works
Starting from the loan balance, the calculator computes the standard fixed monthly payment for the given rate and term, then walks month by month: each month's interest is the remaining balance times the monthly rate, and the rest of the payment (plus any extra amount you specify) reduces principal. The loan is fully paid once the balance reaches zero, which happens sooner than the original term if extra payments are included.
Interest(month) = Balance × monthly rate; Principal(month) = Payment + Extra − Interest(month); Balance = Balance − Principal(month).
Worked example
Scenario: A $250,000 loan at 6% for 15 years, first with no extra payment, then with $200 extra each month.
- Monthly rate 0.5%, 180 payments: payment = 250,000 × 0.005 ÷ (1 − 1.005^−180) = $2,109.64.
- Month 1: interest $1,250.00, principal $859.64, balance $249,140.36.
- With no extra payment, total interest is $129,735.85 over 180 months.
- Adding $200 a month pays the loan off in 157 months and cuts interest to $110,816.99.
Result: $2,109.64 a month; an extra $200 a month saves about $18,919 in interest and 23 months.
Reading an amortization schedule
Early payments on an amortizing loan typically contain more interest and less principal; that balance shifts over time. The schedule helps show how quickly principal falls and how extra principal payments could change interest cost and payoff timing.
Tips and common mistakes
- Confirm with your lender that extra payments go to principal, not future installments.
- The table shows the first 12 months; the pattern — interest falling, principal rising — continues to the end.
- Even a one-off lump sum early in the loan saves more than the same amount paid near the end.
Assumptions & Limitations
- Extra payments are assumed to apply entirely to principal, which is standard for most mortgages and installment loans.
- Uses a fixed rate for the full amortization period.
- The displayed schedule shows the first 12 rows for readability; the totals reflect the complete schedule.
- Some loans have prepayment penalties — check your loan terms before applying extra payments in real life.
Sources and review
Method: Standard fixed-rate amortization (level-payment annuity) formula with monthly compounding, the method used for installment loans and mortgages. Extra payments are applied to principal each month.
Sources:
- Consumer Financial Protection Bureau (CFPB) consumer guidance on loan payments, interest and amortization.
Last reviewed: October 2026 by Faheem Ali, founder of CalculatorAnything. The method and examples are provided for transparency; results remain estimates and may contain errors.
Results are estimates for planning and comparison, not financial advice or a lender's quote. Rates, fees, tax rules and regulations vary by country and change over time; confirm figures with your lender or a licensed adviser. Spotted an error? Tell us — see our editorial policy for how corrections are handled.