Simple Interest Calculator

Estimate simple interest earned, total amount, annual interest, monthly interest, and inflation-adjusted ending value using principal, rate, and time.

Calculate Simple Interest

Simple Interest = Principal × Rate × Time. Unlike compound interest, interest is calculated only on the original principal.
Your result will appear here.

How the simple interest calculator works

Principal:
The original amount stays constant for interest calculations.

Simple interest:
Interest is calculated only on the original principal, not on prior interest earned.

Total amount:
The calculator adds the interest earned to the principal.

After-tax and inflation view:
The calculator also estimates after-tax interest and inflation-adjusted ending value.

Why simple interest matters

Simple interest is easy to understand and is useful for straightforward estimates involving principal, rate, and time. It is especially useful when you want a quick, linear interest estimate without compounding.

This tool is best for planning estimates and basic comparisons.

What your result means

Your result shows interest earned, ending amount, annual and monthly interest estimates, after-tax interest, and inflation-adjusted ending value based on the assumptions entered.

Simple interest calculator tips

Frequently asked questions

What is simple interest?

Simple interest is interest calculated only on the original principal amount and not on accumulated interest.

How is simple interest different from compound interest?

Simple interest does not add earnings back into the balance for future growth, while compound interest does.

Can I use months or days?

Yes. This calculator converts months and days into a year-based time value for the estimate.

Is this a guaranteed result?

No. This is only an estimate based on the rate, time, and assumptions you enter.