Simple Interest Calculator 🔒 Your data never leaves your browser.
Calculate simple (non-compounding) interest on a principal.
About this tool
This simple interest calculator works out interest earned on a principal at a fixed annual rate over a number of years — but unlike a compound interest calculator, it never re-invests the interest it generates. Simple interest is calculated only on the original principal, every single period, so the amount you earn each year stays flat and the total grows in a straight line rather than curving upward over time. For example, $1,000 at 5% for 3 years earns $150 in interest — exactly $50 a year, three years running — for a total of $1,150.
This distinction matters: compound interest pays interest on interest, so its growth accelerates the longer money sits; simple interest never does, which is why it is used for things like short-term loans, certain bonds and basic promissory notes where the math needs to stay predictable. Figures update as you type, calculated entirely in your browser — nothing is sent anywhere. If you want to see how the same numbers behave when interest compounds, try the compound interest calculator for comparison.
Frequently asked questions
When would a bank or loan actually use simple interest instead of compound?
Simple interest shows up in short-term loans and some auto loans, certain bonds, and basic promissory notes — situations where interest is calculated once over a fixed term rather than being recalculated and re-added to a growing balance periodically. Most savings accounts, credit cards, and mortgages use compound interest instead, since it lets the lender (or the saver) earn interest on previously accumulated interest.