Toolgeist › Math & Unit

Simple Interest Calculator — Free Online Calculator

Simple Interest solves I = P × r × t — I = interest earned, P = principal, r = annual rate, t = time in years. Enter your known values and the calculator solves for the rest instantly. All processing happens client-side in your browser, with nothing sent to a server. Free, unlimited, and no registration needed.

How to use Simple Interest

1. Enter your known values in the fields.
2. The result updates instantly as you type.
3. Copy or note down the result.

Frequently asked questions

What formula does Simple Interest use?

I = P × r × t — I = interest earned, P = principal, r = annual rate, t = time in years.

Can I use it on my phone?

Yes. The layout adapts to small screens and behaves the same on mobile as on desktop.

Is my input saved anywhere?

No. Values stay in your browser and are gone as soon as you close the tab.

Related Math & Unit tools

• Roman Numerals
• Area Converter
• Discount Calc
• Voltage Divider
• Standard Dev
• Determinant

Browse all 738 free tools on Toolgeist →