Simple Interest Calculator
Calculate interest earned on a principal at a fixed annual rate.
Simple Interest Calculator
Estimate simple interest before fees, taxes, or repayment timing.
Principal is the starting amount borrowed or invested.
Use annual rate unless another period is clearly required.
Months and days are converted into years for the formula.
Simple interest
Based on your inputs using simple interest without compounding.
Simple interest
Principal × rate × time.
Total amount
Principal plus simple interest.
Principal
Starting amount.
Interest rate
Annual rate.
Time period
Converted to years.
Interest per year
Simple average per year.
Effective total return
Interest ÷ principal.
Solved variable
Simple interest
Finance-focused
Estimate interest for basic savings, notes, and loan scenarios.
No compounding
Simple interest is calculated only on the original principal.
Formula-driven
Solve for interest, total amount, principal, rate, or time.
Dynamic Simple Interest Insights
Example Calculations
Click any example to load it into the calculator.
What Simple Interest Means
Original principal
Simple interest is calculated only on the original principal.
No compounding
Interest does not earn interest on previous interest.
Linear growth
Interest grows in a straight line over time.
Common uses
Used for basic loans, notes, and educational examples.
Simple Interest vs Compound Interest
Simple interest
Simple interest uses only the original principal and grows in a straight line.
Compound interest
Compound interest uses principal plus accumulated interest and can accelerate over time.
Principal, Rate, and Time Explained
Principal
The starting amount borrowed or invested.
Rate
The interest percentage per year. Divide percentage rate by 100 before calculating.
Time
How long money is borrowed or invested. Units must match the rate period.
Savings and Loan Use Cases
When Simple Interest Can Mislead
Savings products
Many savings products use compound interest or APY.
Loans
Many loans amortize with periodic payments.
Fees and taxes
Fees and taxes can change real cost or return.
Daily accrual
Interest may accrue daily even if stated annually.
Simple Interest Formula
Simple Interest = Principal × Rate × Time
Total Amount = Principal + Simple Interest
Principal = Simple Interest ÷ (Rate × Time)
Rate = Simple Interest ÷ (Principal × Time)
Time = Simple Interest ÷ (Principal × Rate)
Principal is the starting amount, rate is written as a decimal, and time is usually measured in years. Divide percentage rates by 100 before calculating, and convert months or days into years when using an annual rate.
Frequently Asked Questions
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