About the Simple Interest Calculator
Calculate simple interest with I = P × r × t. Enter the principal, annual rate and time in years, months or days to get the interest and the total amount.
Key features
- Interest and total amount (I = P × R × T)
- Time in years, months or days
- Clear formula breakdown
- Comparison with compound interest
- Multiple currencies
- Results update as you type
Simple interest made simple
Simple interest grows in a straight line: the same amount every year, based only on the original principal. It's easy to calculate and common in short-term loans and fixed-income products.
Formula
Interest I = P × R × T
Total A = P × (1 + R × T)
Worked example
5,000 at 6% for 3 years:
- I = 5,000 × 0.06 × 3 = 900
- A = 5,000 + 900 = 5,900
For 18 months: T = 1.5, so I = 5,000 × 0.06 × 1.5 = 450.
Simple vs compound interest
10,000 at 8%:
| Years | Simple interest | Compound (yearly) |
|---|---|---|
| 1 | 10,800 | 10,800 |
| 5 | 14,000 | 14,693 |
| 10 | 18,000 | 21,589 |
| 20 | 26,000 | 46,610 |
The gap widens dramatically over long periods.
Solving for other values
| Find | Formula |
|---|---|
| Principal | P = I ÷ (R × T) |
| Rate | R = I ÷ (P × T) |
| Time | T = I ÷ (P × R) |
For estimates and study only; not financial advice.
Related calculators
See the compounding effect with the Compound Interest Calculator, or calculate payments with the Loan Calculator.
How to use the Simple Interest Calculator
- Enter your numbers in the fields above. Units and options can be changed at any time.
- The result updates instantly as you type; there's no calculate button to press.
- Check the breakdown under the main result for the details behind the number.
- Adjust the inputs to compare scenarios, for example a different rate or term.