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Interest Rate Calculator

Find the interest rate on a loan from the amount, monthly payment and term. Shows the APR, effective yearly rate and total interest. Free.

Interest rate (APR)
4.999%
Monthly rate
0.4166%
Effective yearly rate (APY)
5.116%
Total paid
22,645.20
Total interest
2,645.20

Work backwards to the interest rate

Dealers and lenders often quote a monthly payment rather than a rate. This calculator works backwards from the loan amount, the payment and the number of months to find the interest rate the loan really charges. Borrow $20,000 and pay $377.42 a month for 5 years, and the rate is 5.0% a year. There's no simple formula for this, so the calculator searches for the rate numerically, to a thousandth of a percent.

How to use it

  1. 1

    Enter the loan amount

    The amount borrowed.

  2. 2

    Add the payment and term

    The monthly payment and the loan length in years.

  3. 3

    Read the rate

    The yearly rate (APR), the monthly rate and the effective rate.

Frequently asked questions

How do you calculate an interest rate from a payment?

Solve P = M × (1 − (1 + r)^−n) ÷ r for r. There's no closed form, so it's found by trial (bisection), which is what this tool does.

What's the difference between APR and effective rate?

APR is the monthly rate × 12. The effective yearly rate includes monthly compounding: (1 + r)^12 − 1.

Why does it say no rate fits?

If the payments add up to less than the amount borrowed, no positive interest rate can produce them.

Is my data sent anywhere?

No. Everything is calculated in your browser.

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