Simple Interest Calculator
Calculate simple interest on a principal over a period of time.
Result
Results are estimates for general information only and are not professional advice.
What simple interest is
Simple interest is interest charged only on the amount you originally borrowed or deposited, never on interest that has already accumulated. That single difference makes it far easier to predict than compound interest: the amount added each year is identical from the first year to the last. You will meet it on short-term personal loans, car financing in some markets, government bonds and many fixed-term deposits.
The formula behind it
The calculation is I = P × r × t, where P is the principal, r is the annual rate written as a decimal, and t is the time in years. A deposit of 10,000 at 5% for 3 years earns 10,000 × 0.05 × 3 = 1,500 in interest, giving a final balance of 11,500. Because nothing compounds, doubling the term simply doubles the interest.
How to use this calculator
Enter the principal, the annual rate as a percentage and the time in years, then press Calculate. You will see the interest earned or owed and the final balance. For periods shorter than a year, enter the fraction — six months is 0.5, ninety days is roughly 0.25.
Simple or compound?
Over one year the two are identical. Beyond that, compound interest always produces more, so borrowers benefit from simple interest and savers benefit from compounding. When a lender quotes a "flat rate", they usually mean simple interest on the full original balance even as you pay it down — which costs more than the number suggests. Compare offers using APR instead.
Frequently Asked Questions
What is the Simple Interest Calculator?
Calculate simple interest on a principal over a period of time. It runs instantly in your browser and is completely free to use.
What do I need to enter to use the Simple Interest Calculator?
The Simple Interest Calculator asks for the following values (3): Principal, Annual rate (%), Time (years). Fill them in and the result appears immediately — the calculation runs on your own device, so nothing you type is sent to a server.
How accurate is the Simple Interest Calculator?
The Simple Interest Calculator uses standard, widely-accepted formulas, so its figures are reliable estimates for everyday planning. They are not a substitute for advice from a qualified professional.
Is the Simple Interest Calculator free, and do I need an account?
Yes. The Simple Interest Calculator — and every other calculator on Calculatis — is completely free, with no registration, no download and no limit on how often you use it.