If you know any three of a loan’s four terms (principal, interest rate, payments remaining, and payment amount), this calculator will help you to find the missing term. For example, if you know the interest rate, the payments remaining, and the payment amount, this calculator will compute the current payoff amount of the loan. All results should be interpreted as close approximations (testing to date has shown results to be accurate within .002% of the actual).

Enter the three known values in the appropriate entry fields and click “Compute.” Note that when trying to find the interest rate, you should select a “guess” from the pull-down menu by the same name. The closer your guess is to the actual interest rate, the faster the calculator will arrive at a result. If you don’t select a “guess” the calculator automatically starts out at a 10% guess and works up or down until it finds a close approximation. If it turns out the actual rate is 19.95% it could take the calculator as many 56,000 iterations to find the answer. On the other hand if you had “guessed” 19% the calculator’s iterations would be reduced significantly.