➕ Simple Interest Calculator
Enter your principal, annual interest rate, and time period to instantly calculate simple interest and the total amount. Also see a side-by-side comparison with compound interest on the same numbers.
➕ Enter Loan or Investment Details
Summary
⚖️ Simple vs. Compound Interest (Same Numbers)
Assuming compound interest calculated annually, for comparison.
| Type | Total Interest | Total Amount |
|---|---|---|
| Simple Interest | $0 | $0 |
| Compound Interest (annual) | $0 | $0 |
How Simple Interest is Calculated
Simple Interest Formula
P = Principal
R = Annual interest rate (%)
T = Time in years
Worked Example
$5,000 principal, 6% annual rate, 3 years:
Total Amount = 5,000 + 900 = $5,900
Solving for Rate or Time
Time = (SI × 100) ÷ (P × R)
Try These Examples
Frequently Asked Questions
Simple Interest Calculator - Find Interest and Total Amount Fast
Simple interest is the most straightforward way interest can be calculated - it's based only on the original amount, for the whole time period, with no compounding. This makes it easy to calculate by hand, and it's still used for many short-term loans, some auto loans, and basic financial education. This calculator gives you the exact interest earned or owed, the total amount, and shows how it compares to compound interest on the same numbers.
Quick example: $5,000 at 6% for 3 years $900 interest, $5,900 total
Simple Interest vs. Compound Interest
The key difference is what the interest is calculated on. Simple interest is always calculated on the original principal, so it grows by the same dollar amount every year - a straight line. Compound interest is calculated on the principal plus all previously earned interest, so the dollar amount of growth increases every year - a curve that accelerates over time. Over a short period like 1-3 years, the difference is often small. Over 10, 20, or 30 years, compound interest can produce a dramatically larger total.
Where Simple Interest Is Actually Used
- Short-term personal loans: Many personal loans, especially shorter-term ones, use simple interest calculations.
- Some auto loans: Many car loans use simple interest calculated daily on the remaining balance.
- Certain bonds and notes: Some fixed-income instruments pay simple interest at regular intervals rather than compounding it.
- Education and quick estimates: Because the math is simpler, it's commonly taught first and used for back-of-envelope estimates.
Most savings accounts, credit cards, mortgages, and long-term investments actually use compound interest - so if you're evaluating a long-term financial product, double check which type of interest applies, since the difference compounds (literally) over time.
How this calculator works, and where the numbers come from
The Simple Interest Calculator applies the standard formula for this calculation to the values you enter and updates the result as you type. The calculation itself happens in your browser, and the page explains the method so you can check any result by hand.
Please note: Projections assume the inputs you enter stay constant; real returns vary. Results are estimates, not financial advice.
Sources and further reading
Learn more
Read our guide: Compound Interest and the Rule of 72, Checked Against the Math