TetraKits
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. The TetraKits Simple Interest Calculator runs entirely in your browser — free, private, and ready on mobile or desktop.
Overview
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.
How to use the simple interest calculator
- Enter principal — Type the initial amount borrowed or invested. Example: $5,000 loan principal.
- 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).
- Read interest and total — See interest (I = PRT) and total amount (P + I). For reinvested interest, use the compound interest calculator.
Common use cases
- Enter principal: Type the initial amount borrowed or invested.
- Set rate and time: Enter annual interest rate as a percent and time in years.
- Read interest and total: See interest (I = PRT) and total amount (P + I).
- Bookmark for quick access: Save the tool for repeat tasks without installing an app.
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.
