Simple Interest Calculator
Calculate simple interest on a loan or savings balance from principal, rate and time period, free and instant right in your browser.
Enter Values
Minimum 0
Minimum 0
Minimum 0
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the principal, the annual rate and the number of years.
- Press Calculate.
How it works
Simple interest is charged only on the original principal: Interest = P × r × t ÷ 100. Unlike compound interest, it doesn't earn interest on interest.
Worked example
$1,000 at 5% for 2 years. Interest = 1,000 × 5 × 2 ÷ 100 = $100, so $1,100 in total.
Common mistakes
- Using simple interest where compound interest applies — most savings and loans compound.
- Entering the rate as a decimal (0.05) instead of a percent (5).
Frequently asked questions
When is simple interest used?
Some short-term loans and bonds. Most savings accounts and mortgages use compound interest.
How is it different from compound interest?
Simple interest is charged only on the original principal; compound interest also earns interest on the interest already added, so it grows faster over time.
What's the formula?
Interest = principal × rate × time ÷ 100, where rate is the annual percentage and time is in years.
Related tools
- Compound Interest Calculator
- Loan Repayment Calculator
- Savings Rate Calculator
- APY Calculator
- Rule of 72 Calculator
- Savings Goal Calculator
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Cite this tool
Zerdly. (2026). Simple Interest Calculator. Retrieved from https://www.zerdly.com/tools/simple-interest-calculator/
Tip: Enter any known values to calculate the remaining results.
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