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Interest Rate Calculator

Find the interest rate you are really paying. Enter the amount borrowed, the monthly payment and the number of payments, and the calculator solves for the annual rate — useful for dealer financing, “low monthly payment” offers and checking a lender’s figures.

Quick examples
$
$
months
Your numbers stay in your browser. Nothing is uploaded.
Interest rate (APR)7.42%
Total interest
$4,000.00
Total of payments
$24,000.00
Effective annual rate
7.678%

Saved setups

Save a set of inputs you reuse — your usual rate, your loan, your room sizes — and load it back in one tap.

    Your recent calculations

    Results you calculate here are kept on this device so you can come back to them.

      Formula

      The monthly rate r satisfies: amount = payment × (1 − (1 + r)^−n) ÷ r
      There is no direct formula for r, so it is found numerically by narrowing in on the value that balances the equation
      Annual rate (APR) = r × 12
      Total interest = payment × n − amount

      How to use it

      1. Enter the amount financed after any down payment.
      2. Enter the fixed monthly payment.
      3. Enter the number of monthly payments and read the rate.

      Worked examples

      Borrowing $20,000 and paying $400 a month for 60 months

      Interest rate (APR)
      7.42%
      Total interest
      $4,000.00
      Total of payments
      $24,000.00
      Effective annual rate
      7.678%

      A $300,000 mortgage with a $1,896.20 payment for 360 months

      Interest rate (APR)
      6.5%
      Total interest
      $382,632.00
      Total of payments
      $682,632.00

      A $1,200 phone paid off at $50 a month for 24 months — a 0% plan

      Interest rate (APR)
      0%
      Total interest
      $0.00
      Total of payments
      $1,200.00

      A quick sanity check

      If payment × number of payments equals the amount borrowed, the rate is 0%. If it is less, something is missing from the figures and no rate is shown. Fees rolled into the payment show up here as a higher rate, which is the point of the exercise.

      The result is the nominal annual rate with monthly compounding, the same basis lenders use to quote APR on installment loans.

      Questions people ask

      What interest rate is $400 a month for 60 months on a $20,000 loan?

      7.42% APR. You repay $24,000, of which $4,000 is interest.

      How do I find the interest rate from the monthly payment?

      It has to be solved by trial and error or with a calculator like this one. For example, $1,896.20 a month for 360 months on $300,000 works out to 6.5%.

      Is a 0% financing offer really 0%?

      Check that payment × months equals the price. $50 a month for 24 months on a $1,200 phone is exactly 0%; if the same phone were $55 a month, the rate would be about 9.3%.

      Related calculators

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