Flat, non-compounding interest
Interest is charged only on the original principal, exactly as I = P × r × t, with no interest on interest.
CalculatorsRuns in your browser
Simple Interest Calculator
Interest on a principal at a flat rate — no compounding.
- Input
- No upload needed — instant
- Privacy
- Nothing is uploaded
- Cost
- Free · no sign-up · no watermark
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Overview
About the Simple Interest Calculator
Calculate simple interest from a principal, an annual rate and a time period, showing the interest earned, the total amount at the end and the interest per year.
Simple interest is the most intuitive form of interest: a fixed percentage of the original amount, charged each year, with no interest on interest. Enter a principal, an annual rate and a time in years and this calculator returns the interest, the total at the end and how much accrues every year.
The formula
I = P × r × t
A = P + IP is the principal, r the annual rate as a decimal and t the time in years. A is the total amount at the end.
When it is used
It is the model behind many short-term and personal loans, some government bonds and most classroom examples, and it is the baseline against which compound growth is usually compared.
Private and precise
Every figure is worked out in your browser with standard financial formulas. Nothing you type is uploaded, stored or sent anywhere.
Step by step
How to use the Simple Interest Calculator
Enter the principal amount and choose a currency.
Add the annual rate as a percentage and the period in years (decimals allowed).
Read the total interest, the final amount and the interest per year.
Why use it
Benefits and common use cases
What this tool is good for, and what it deliberately does not try to do.
The whole picture at once
See the interest, the end amount and the yearly accrual together, so a flat-rate loan is easy to compare.
Good for short-term loans
The model behind many personal loans, some bonds and most classroom examples of interest.
Questions
Frequently asked questions
Short, honest answers about quality, limits and privacy.
How is simple interest different from compound?
Simple interest is charged only on the original principal, so it grows in a straight line. Compound interest is charged on the principal plus past interest, so it curves upward and is much larger over long periods.
Can I use months instead of years?
Enter the time as a decimal of a year — six months is 0.5, nine months is 0.75 — and the result scales correctly.