Interest Calculator (Simple Interest)
Calculate simple interest earned or owed over time and the total amount. Simple interest does not compound; it grows linearly over time.
Inputs
$
%
Results
Time (years)3
Interest$1,500.00
Total$11,500.00
Formula: I = P × r × t (simple interest)
How to use it
- Enter the principal amount (starting balance).
- Enter the annual interest rate.
- Enter the time period (years, or convert months/days).
- Review interest earned/owed and total amount.
Key formulas
- Simple interest
- I = P × r × t
- Total amount
- A = P + I
FAQ
Simple interest is calculated only on the principal. Compound interest adds interest to the balance, so future interest is earned on interest as well.
These formulas use years. If you have months or days, convert to years (months/12, days/365 as an approximation).
APR is the annual rate. For simple interest, the model assumes the rate applies evenly over time without compounding.
Credit cards typically compound interest and include fees, daily rates, and minimum payment rules. Simple interest is a simplified model.
0% yields zero interest. Negative rates are uncommon; if modeling a loss, you can enter a negative rate but interpret results carefully.
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Disclaimer
Estimates only. Many real-world products compound interest and include fees and special rules. Confirm with official disclosures.