Simple Interest Calculator
Calculate simple interest.
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Your inputs are processed locally in your browser and are not uploaded or stored by us.
Calculate simple interest, which is determined solely on the original principal over a specific time period. This is a pure mathematical calculation and does not include real-world factors like taxes, fees, inflation, or institution-specific rules.
How to calculate simple interest
- Enter the initial principal amount.
- Enter the annual interest rate as a percentage (e.g., enter 5 for 5%).
- Enter the time period in years.
- Click "Calculate" to determine the total interest and final amount.
Simple Interest Formula
I = P × r × t
A = P + I
Where P is the principal, r is the annual interest rate expressed as a decimal (e.g., 5% = 0.05), and t is the time in years. The interest I is calculated by multiplying these three factors together. The total amount A is the sum of the principal and the earned interest.
Example calculation
Principal1000
Annual rate5%
Time2 years
I = 1000 × (5 / 100) × 2 = 100
Total amount = 1000 + 100 = 1100
Result: Interest = 100, Total = 1100
Notes
- The principal and time in years must be 0 or greater (time = 0 results in 0 interest).
- Negative interest rates are fully mathematically supported (e.g., a rate of -5% on 1000 over 2 years produces an interest of -100 and a total amount of 900).
- This calculator is for educational and mathematical purposes, and does not provide financial advice.
- Calculations use JavaScript floating-point numbers, so some decimal results may be approximate.
- Your calculator inputs are processed locally in your browser and are not uploaded or stored by us.