Loan interest calculator
Use this loan interest calculator to compare monthly payments and total interest across three repayment methods: equal payments (amortized), equal principal, and interest-only with the principal repaid at maturity. A monthly amortization schedule shows how much of each payment goes to principal and interest.
Actual loan terms vary by lender. Treat these results as an estimate and confirm the final figures with your lender.
Show the monthly schedule
| Month | Payment | Principal | Interest | Balance |
|---|
How to use
- Enter the loan amount.
- Enter the annual interest rate as a percentage. Example: 5.0
- Enter the repayment term in months. Example: 30 years is 360
- Choose a repayment method and open the monthly schedule to see principal and interest for each payment.
How it works
The three methods work as follows, where r is the monthly rate (annual rate ÷ 12 ÷ 100) and n is the number of months.
Equal payments: every payment is the same. Monthly payment = P × r × (1 + r)^n ÷ ((1 + r)^n − 1).
Equal principal: you repay P ÷ n of principal each month plus interest on the remaining balance, so the first payment is the largest and payments shrink over time.
Interest-only: you pay P × r of interest each month and repay the whole principal in the last month.
At a 0% rate there is no interest.
Example
Take a loan of 100,000 at 5% over 360 months with equal payments. The monthly payment is 536.82 and the total interest is 93,255.20.
For 100,000 at 3% over 60 months: equal payments cost 1,796.87 a month; equal principal starts at 1,916.67 and falls to 1,670.83 in the last month; interest-only costs 250.00 a month and 100,250.00 in the last month.
Good to know
- Early payments on an equal-payment loan are mostly interest, and the share going to principal grows over time, as the U.S. Consumer Financial Protection Bureau describes.
- Interest-only repayment has the lowest monthly payments but the highest total interest, because the full principal stays outstanding until the end.
- Amounts are shown to two decimal places. The last equal-payment row absorbs rounding differences, and equal-principal rows are rounded one by one, so a column total can differ from the summary by a few cents.
- The calculator assumes a fixed interest rate for the whole term. It does not include fees, insurance, taxes, or early-repayment charges.
- Results are estimates. Confirm the exact payment with your lender.
Frequently asked questions
What is an equal-payment loan?
You pay the same amount each month. Early payments are mostly interest, and the principal share grows over time.
How is a 0% loan calculated?
There is no interest, so the monthly payment is the principal divided by the number of months.
Does this include early repayment fees?
No. Check your lender's terms for any early repayment fee.
Sources
Last updated: 2026-10-29