01
A 3-year loan
Enter a principal of $10,000, an annual rate of 5% and a time of 3 years to get $1,500 in interest, a final balance of $11,500, and an average monthly interest of about $41.67.
Simple Interest Calculator
CalculatorsCalculate simple interest and the final amount on any principal and rate — free and instant.
About
About the Simple Interest Calculator
Works out the interest earned and final balance on a principal amount using simple (non-compounding) interest.
Students learning the simple-interest formula use it to check their own hand calculations, while anyone comparing a simple-interest loan or bond against a compounding option uses it to see the plain interest on its own. It's one of many free calculators on Toolapt, and like every tool here, it's free to use with no sign-up and no limit on how many times you run it.
Examples
Simple Interest Calculator examples
3 worked examples
02
A short 6-month deposit
Enter a principal of $5,000, a rate of 4% and a time of 0.5 years to get $100 in interest and a final balance of $5,100.
03
Comparing to compound interest
With the same principal, rate and time, simple interest always gives a smaller total than compound interest, since simple interest never earns interest on interest already accrued.
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FAQ
Frequently asked questions
Quick answers to common questions about the Simple Interest Calculator.
What does the Simple Interest Calculator do?
It calculates the interest earned and final balance on a principal amount using simple (non-compounding) interest over a chosen number of years.
Is the Simple Interest Calculator free to use?
Yes. It's free, with no sign-up, no watermark and no limit on how many times you use it.
Is my input safe when I use this tool?
Yes. The principal, rate and time you enter are processed entirely on your own device — nothing is sent to a server.
What's the difference between simple and compound interest?
Simple interest is calculated only on the original principal every period, while compound interest is calculated on the principal plus any interest already earned. Simple interest always grows in a straight line; compound interest accelerates over time.
Can I use decimal years, like 2.5 years?
Yes. The time field accepts decimals, so you can calculate interest for part of a year.
What happens if I enter a negative number?
The calculator shows a message asking for non-negative values — principal, rate and time all need to be zero or greater.
What does "Monthly interest (avg.)" mean?
It's the total interest earned divided evenly across the number of months in the time period, so you can see roughly how much interest accrues per month on average.
Can I use the Simple Interest Calculator on my phone?
Yes. The page is fully responsive and works on mobile, tablet and desktop browsers alike.