Add one-time extra payments
One-time payments are applied in addition to the regular payment in the month you choose (0 = none).
Compare against an alternative loan
Optional: enter an alternative loan term and rate to see how the monthly payment, total interest, and payoff time compare to the loan above.
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Calculation details
Planning estimate only, not financial, tax, or legal advice. Verify assumptions and current rules before making decisions.
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What does this calculator estimate?
The amortization calculator estimates your fixed monthly payment for a loan, shows the full payment-by-payment schedule with interest and principal, and quantifies how an extra monthly payment shortens the term and reduces total interest.
What is amortization?
Amortization is the process of paying off a loan in equal installments that cover both interest and principal. Early payments are mostly interest because the balance is largest; over time the split shifts so that later payments are mostly principal. The amortization schedule shows exactly how much of each payment goes to interest versus principal and how the balance declines.
How extra payments help
Every extra dollar you pay toward principal reduces the balance on which future interest is charged, so it compounds in your favor. The impact is large on long, high-rate loans: a modest extra monthly payment can cut years off a 30-year mortgage and save tens of thousands in interest. This calculator shows the sooner payoff date and the interest saved.
Interest, principal, and the total cost
The total cost of a loan is the principal plus all interest paid over its life. Because interest accrues on the declining balance, a shorter term or lower rate reduces total interest, even though the monthly payment may be higher. Comparing the total-interest column across scenarios shows the real cost difference.
How this calculator works
Formula
Payment = amount x r/12 / (1 - (1 + r/12)^-n); extra payments cut term length and total interest proportionally.
Worked example
A $200,000 loan at 6.5% for 30 years: $1,264.14 a month in principal and interest; the 15-year comparison at 5.75% is computed alongside.
Assumptions to verify
- The loan uses a fixed annual interest rate and standard monthly compounding.
- Payments are made monthly on schedule, with interest calculated on the remaining balance.
- Fees, taxes, insurance, and prepayment penalties are excluded.
- Extra payments are applied to principal in the month they are made.
Frequently asked questions
What is an amortization calculator?
An amortization calculator estimates the monthly payment on a fixed-rate loan and shows a full schedule of how each payment is split between interest and principal, plus the declining balance. It can also show the effect of extra monthly payments.
How is the monthly payment calculated?
The payment uses the standard formula P × r ÷ (1 − (1 + r)^−n), where P is principal, r is the monthly interest rate, and n is the number of monthly payments. For example, a $200,000 loan at 6.5% for 30 years has a payment of about $1,264.
Does paying extra each month really save that much?
Yes. Because interest is charged on the remaining balance, extra principal payments reduce future interest. A $200 monthly extra on the example loan pays it off about 9 years early and saves roughly $90,000 in interest.
What is the difference between interest and principal in a payment?
The interest portion is the cost of borrowing for that month, calculated on the current balance; the principal portion is what actually reduces what you owe. Early in a loan, most of the payment is interest; near the end, most is principal.
Should I make extra payments or invest the money?
It depends on the guaranteed return you get. Paying down a 6.5% loan is a risk-free 6.5% return; investing might earn more but carries risk. Many people choose extra principal payments for the certainty, after confirming their lender allows them without penalty.
Cite this tool
BoringToolsKit. “Amortization Calculator.” boringtoolskit.com/amortization-calculator/ (reviewed August 2026). Free to reference in articles, syllabi, and answer posts with a link.
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