Simple Interest Calculator
Work out flat, non-compounding interest fast.
How to use
- 1 Enter the principal amount.
- 2 Enter the annual interest rate as a percent.
- 3 Enter the term in years.
- 4 Read off the interest earned and the final total.
About Simple Interest Calculator
The Simple Interest Calculator works out the flat interest on a sum of money using the classic formula interest = principal × rate × time.
Enter the principal, the annual interest rate as a percent and the term in years, and it returns the interest earned over the whole period along with the final total of principal plus interest.
Simple interest is the right model for short-term loans, fixed deposits and many informal lending arrangements where interest does not roll up on itself.
Unlike compound interest, it accrues the same flat amount each year — interest is charged only on the original principal, never on interest already earned.
That makes it easy to estimate the cost of a loan or the payout on a savings note before you commit.
Doing the multiplication by hand is straightforward, but it is easy to slip a decimal point or mix up the percentage, especially across multi-year terms.
This calculator does the arithmetic for you, rounds money to two decimal places and shows its working so you can copy the figures straight into a budget or contract.
Everything runs locally in your browser, so your numbers never leave your device.
FAQ
How is simple interest different from compound interest?
Simple interest is charged only on the original principal, so the same flat amount accrues each year. Compound interest is charged on the principal plus any interest already earned, so it grows faster.
Can I use a fractional term, like 6 months?
Yes. Enter the term in years as a decimal — 6 months is 0.5, and 18 months is 1.5.