Amortizing Loan Calculator
Calculate the monthly payment and amortization schedule for any fixed-rate loan.
A worked example
Running this tool on current national benchmarks (Federal Reserve / Freddie Mac via FRED (St. Louis Fed)) — swap in your own numbers to see how the result moves.
- Solve for
- Monthly payment
- Loan amount
- $25,000
- Interest rate (APR)
- 7.50%
- Loan term
- 5 years
- Extra monthly payment
- $0
$25,000 at 7.50% over 5 years
- Loan amount$25,000
- Monthly payment$500.95
- Total interest$5,057
How the monthly payment changes with loan amount
Holding the other inputs at the example above, here is how the result moves as loan amount changes.
| Loan amount | Monthly payment | Loan amount |
|---|---|---|
| $12,500 | $250.47 | $12,500 |
| $25,000 | $500.95 | $25,000 |
| $37,500 | $751.42 | $37,500 |
| $50,000 | $1,001.90 | $50,000 |
The math behind it
This is a standard fixed-rate amortization. The monthly payment is calculated so that equal payments retire the full balance by the end of the term at the given rate. Each month, interest is charged on the outstanding balance and the rest of the payment reduces principal — so early payments are mostly interest and later ones mostly principal. You can solve for the payment from a loan amount, or solve for the amount a given payment supports. An optional extra monthly payment is applied straight to principal.
Assumptions & limits
- A fixed interest rate is applied for the entire term.
- Interest compounds monthly on the outstanding balance.
- Any extra monthly payment reduces principal directly, shortening the term and cutting total interest.
- No origination fees, insurance or taxes are included — the figure is pure principal and interest.
Common questions
Why is so much of my early payment interest rather than principal?
Interest each month is charged on the balance you still owe, which is largest at the start. So early payments are mostly interest and only a little principal. As the balance shrinks, the interest portion falls and more of each fixed payment goes to principal — which is why the payoff accelerates near the end.
How much does an extra monthly payment save?
Because extra payments go entirely to principal, they remove that balance from every future interest calculation. Even a modest amount added each month can shorten the term by months or years and cut total interest noticeably. Enter an extra payment to see the exact interest saved for your loan.
What is the difference between solving for the payment and solving for the amount?
Solve for the monthly payment when you know how much you want to borrow and need the payment. Solve for the loan amount when you know the payment you can afford and want to know how large a loan it supports at a given rate and term. The math is the same amortization run in reverse.