How do I find the interest rate on a loan if I only know the payment?

There's no direct algebraic formula to isolate the rate from the standard loan payment equation, so it must be found numerically — testing rates until the payment they produce matches the actual payment.

Why does this show an annual rate when I entered a monthly payment?

The calculator first solves for the monthly rate implied by your payment, then multiplies it by 12 to express it as a nominal annual rate, which is the conventional way loan rates are quoted.

Loan Interest Rate Calculator — Find the Rate

Why this can't be solved with a simple formula

The standard loan payment formula is easy to use forward (amount, rate and term give you the payment), but there's no way to algebraically isolate the rate when you already know the payment. This calculator solves it numerically instead — testing rates until the payment they'd produce matches the payment you entered.

payment = P × r / (1 − (1 + r)^−n)

Where P is the loan amount, r is the monthly rate (what we're solving for), and n is the term in months.

Common uses

Verifying a quote: checking that the rate a lender quoted actually matches the payment and term they gave you.
Comparing offers: when two lenders quote a payment and term but not a clear rate, this puts them on equal footing.
Reverse-engineering old loans: figuring out the rate on an existing loan when you only know the payment and remaining term.

Frequently asked questions

What if the payment doesn't even cover the loan amount?

If the total of all payments (payment × number of months) is less than the loan amount, there's no valid interest rate that fits — the loan would never be paid off. The calculator flags this case directly.

Is the result the same as APR?

This gives the nominal annual interest rate implied purely by the amount, payment and term. Real APR quotes sometimes bundle in fees, which this calculator doesn't account for since it only has payment, amount and term to work with.