TetraKitsSimple Interest Calculator
Calculate simple interest with the classic I = P × R × T formula. Enter principal, annual rate, and time in years — see interest earned and total amount. Compare against compound growth with one click.
Read: Simple Interest Calculator Guide: I = Prt Formula Explained →
- Free to Use
- No Signup
- Privacy Friendly
How to calculate simple interest
- 1
Enter principal
Type the initial amount borrowed or invested. Example: $5,000 loan principal.
- 2
Set rate and time
Enter annual interest rate as a percent and time in years. Rate is per year; time can be fractional (0.5 = 6 months).
- 3
Read interest and total
See interest (I = PRT) and total amount (P + I). For reinvested interest, use the compound interest calculator.
Simple interest formula
- I — interest earned
- P — principal (initial amount)
- r — annual interest rate (decimal, e.g. 5% = 0.05)
- t — time in years
Example: $10,000 at 5% for 3 years → I = 10,000 × 0.05 × 3 = $1,500 interest, $11,500 total.
Why Use This Tool?
Clear Formula
See I = Prt applied with your numbers step by step.
Flexible Time
Enter duration in days, months, or years.
Live Results
Interest and total update as you type.
Private
Financial data stays on your device.
Frequently Asked Questions
What is the simple interest formula?
I = P × R × T — Interest = Principal × Rate (decimal) × Time in years. Total = P + I.
When is simple interest used?
Short-term loans, some bonds, and basic finance textbooks use simple interest. Most savings accounts use compound interest instead.
Can time be in months?
Enter time as a fraction of a year. 6 months = 0.5 years. 90 days ≈ 0.25 years.
How does simple differ from compound interest?
Simple interest applies only to principal each period. Compound reinvests interest — see the compound interest calculator for comparison.
Is this simple interest calculator free?
Yes. Unlimited calculations with no signup.
Simple Interest for Short-Term Loans
Personal loans, pawn shop terms, and intro finance courses use linear simple interest — not compounding. Enter principal, rate, and time to get interest owed and total repayment in one step.
