Interest Rate Calculator

How This Calculator Finds Your Rate

Unlike a typical loan calculator where you enter a rate to find a payment, this tool works backward: you supply the loan amount, the monthly payment you're making (or quoted), and the term, and it solves for the interest rate that makes those three numbers consistent. Because there's no algebraic shortcut to isolate the rate in a standard amortization formula, the calculator uses an iterative numerical method (a bisection search) that narrows in on the rate to a very close approximation, the same general approach spreadsheet functions like RATE use.

Interest Rate vs. APR

The headline interest rate only reflects the cost of borrowing the principal itself. If you enter upfront fees — origination charges, document fees, or points — the calculator also reports an APR, which spreads those fees over the loan term to show the loan's true annualized cost. This is why two loans with the same advertised rate can have different APRs, and why comparing APRs is generally the more reliable way to shop for financing. For a deeper look at how fees affect borrowing costs, try the APR calculator.

A Common Pitfall: Rounded Payments

Real-world loan payments are usually rounded to the nearest cent or dollar, so back-solving for the rate from a rounded payment can produce a slightly different number than the lender's stated rate — usually within a hundredth of a percent. If your result looks a little off from what you expected, try entering a more precise payment amount. Once you know your rate, you can plug it into the loan calculator or amortization calculator to see the full payment schedule.