Simple Interest
Flat interest maths.
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About Simple Interest
The Simple Interest Calculator works out the interest earned on a principal amount using the classic formula: interest equals principal times rate times time, divided by 100. Enter your principal, annual interest rate, and the number of years, and it instantly shows the interest earned and the total amount you will have, all formatted as clean currency.
It is completely free to use with no sign-up, no limits, and no ads getting in the way. Every calculation runs entirely in your browser, so your figures are never uploaded, stored, or shared with any server. Adjust the inputs and the results update in real time.
Frequently asked questions
- How is simple interest calculated?
- Simple interest uses the formula I = P × r × t ÷ 100, where P is the principal, r is the annual interest rate as a percentage, and t is the time in years. The total amount is simply the principal plus the interest. Unlike compound interest, it is charged only on the original principal, never on accumulated interest.
- What is the difference between simple and compound interest?
- Simple interest is calculated only on the original principal, so it grows in a straight line. Compound interest is calculated on the principal plus any previously earned interest, so it grows faster over time. For the same rate and term, compound interest always yields a higher total than simple interest.
- Is this simple interest calculator free?
- Yes, it is 100% free to use with no sign-up, subscription, or usage limits. You can run as many calculations as you like at no cost.
- Is my financial data uploaded or stored anywhere?
- No. All calculations happen entirely in your browser on your own device. Your principal, rate, and time values are never sent to a server, saved, or shared with anyone, so your financial information stays completely private.
- Can I use this for loans and savings?
- Yes. The same simple interest formula applies whether you are estimating interest earned on a savings deposit or interest owed on a simple-interest loan. Enter the principal, the annual rate, and the term in years to see the interest and total amount for either case.
- How do I enter a time period shorter than a year?
- The time field accepts decimals, so enter fractions of a year. For example, use 0.5 for six months, 0.25 for three months, or 1.5 for eighteen months, and the calculator will prorate the interest accordingly.