Interest Rate Calculator

What this calculator does

You've got a loan offer, or maybe one you're already paying off, and you want to know the real rate behind it. That's what this interest rate calculator is for. You type in how much you borrowed, what you pay each month, and how long the loan runs. It works backward and shows you the interest rate sitting inside those numbers. This is handy when a lender leads with a monthly payment but stays quiet about the rate.

How the calculator finds your rate

Here's the thing about interest rates: you can't solve for one with a single clean formula. The standard loan payment formula ties four numbers together (amount, payment, term, and rate), but the rate is tangled inside it in a way that math can't untie in one step.

So the calculator does what a person would do, just much faster. It guesses a rate, works out the monthly payment that rate would create, and checks it against your real payment. Too high? It lowers the guess. Too low? It nudges it up. It repeats until the two payments line up.

Say you borrowed $20,000 and pay $377.42 a month for 60 months. The calculator tests rates until the payment matches, and lands on 5% APR. Over the full term you'd pay about $2,645.20 in interest on top of the $20,000 you borrowed.

Find the rate when all you have is a payment

Plenty of offers lead with the monthly payment because it sounds small. A furniture store, a used car lot, a rent-to-own deal: they'll tell you "$377 a month" and leave the rate off the page.

That's where this helps most. As long as you know the amount, the payment, and how many payments you'll make, you can find the interest rate from the payment itself. Once you see the rate in plain numbers, it's a lot easier to tell a fair deal from an expensive one.

Interest rate vs. APR

This loan interest rate calculator shows the interest rate from the numbers you give it. Your APR may land a bit higher. The interest rate is what it costs to borrow the money itself. The APR also folds in certain lender fees, so it captures the full yearly cost.

Want the APR instead? Subtract any upfront fees from the loan amount before you run the numbers, since the APR is based on the amount you actually receive after fees. And keep in mind that the rate a lender offers you depends on a few things: your credit score (higher scores on the 300 to 850 FICO scale tend to earn lower rates), the length of the loan, whether it's secured by something like a car or home, and the going rates in the wider market.