Interest Rate Calculator

Find the interest rate on a loan given the amount, payment, and term.

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Result

Fill in the fields above, then press Calculate.

Enter your loan amount, monthly payment, and the total number of monthly payments. Click Calculate to find the annual interest rate (APR) on your loan. This is useful when you know your payment details but need to determine the underlying interest rate.

Examples

Auto Loan Rate

If you borrowed $25,000 and pay $477.53/month for 60 months, the calculator determines your APR is approximately 5.50%.

Mortgage Rate Check

A $300,000 mortgage with $1,610.46/month payment over 360 months (30 years) has an APR of approximately 4.50%.

Frequently Asked Questions

What is the difference between APR and APY?
APR (Annual Percentage Rate) is the nominal annual rate without compounding. APY (Annual Percentage Yield) accounts for the effect of monthly compounding and is slightly higher than APR.
How does Newton's method work?
Newton's method is an iterative numerical technique that starts with an initial guess and refines it using the function and its derivative until it converges on the correct rate with high precision.
What if my payment is too low?
The minimum possible payment equals the loan amount divided by the number of months (a 0% rate scenario). If your payment is lower than this, no positive interest rate can produce that payment schedule.
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Quick Tips

Double check your inputs. Ensure units match (e.g., inches vs cm).

Did you know?
Calculators are estimates. Consult professionals for critical decisions.