Simple Interest Calculator
Calculate simple interest and the final amount from principal, rate and time.
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How it works
Simple interest is charged only on the original principal, not on accumulated interest. The formula is I = P × r × t, where P is the principal, r the annual rate as a decimal, and t the time in years. The tool multiplies these to give the interest, then adds it to the principal for the final amount. Unlike compound interest, simple interest grows linearly, which makes it common for short-term loans and some bonds. Currency formatting is configurable and all math runs locally.
I = P × r × t
final = P + I
Common use cases
- Working out the interest on a short-term personal loan.
- Checking the return on a simple-interest savings product or bond.
- Comparing a simple-interest quote against a compound one.
Frequently asked questions
How is simple interest different from compound?
Simple interest is calculated only on the original principal, so it grows by the same amount each period. Compound interest is calculated on principal plus previously earned interest, so it grows faster over time. Use the Compound Interest Calculator for the latter.
What time units does it use?
The rate is annual and time is in years, but you can enter fractional years (for example 0.5 for six months) to handle shorter periods.
Is my data sent anywhere?
No. The calculation happens entirely in your browser. Nothing you enter is uploaded or stored on a server.