Calculate simple interest the classic way, where interest is charged only on the original principal and never on accumulated interest. Enter the principal, the annual interest rate and the time period in years, and the calculator applies the formula I = P x r x t to give you the interest amount and the total balance at the end. Simple interest is common on short-term loans, some bonds and certain fixed deposits, and it is the easiest interest type to reason about because the amount grows in a straight line rather than accelerating. This makes it a useful baseline to compare against compound interest for the same rate and term. The result updates instantly and is computed entirely in your browser.