Free Simple Interest Calculator
Work out simple interest on a principal amount — no signup, nothing sent to a server.
Simple interest
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Total amount
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How to calculate simple interest
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1
Enter the principal amount
Type the original sum being lent, borrowed, or invested.
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2
Enter the annual interest rate
Use the rate quoted for the loan or deposit.
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3
Set the time period
Enter the duration in years or months.
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4
Read the result
Simple interest and the total amount update instantly as you type.
Example use cases
Short-term loans
Work out the interest owed on a loan that accrues interest on the principal alone.
Fixed deposits & bonds
Estimate returns on instruments that pay simple, non-compounding interest.
Comparing loan offers
Check the total repayment on a simple-interest loan before agreeing to terms.
Frequently asked questions
How is simple interest calculated?
Simple interest = (Principal × Rate × Time) ÷ 100, where Rate is the annual percentage and Time is in years. Total amount = Principal + Simple interest.
How is simple interest different from compound interest?
Simple interest is calculated only on the original principal for the whole period. Compound interest is calculated on the principal plus any interest already added, so it grows faster over time. See the Compound Interest Calculator for that version.
Can I enter the time period in months instead of years?
Yes — switch the time unit to "Months" and the calculator converts it to years internally before applying the formula.
Is my financial information sent to a server?
No. The calculation runs entirely in your browser — nothing is transmitted or logged.