Finance Calculators
Simple Interest Calculator
Calculate simple interest on a principal using an annual rate and a time period in years. Interest is calculated only on the original principal; it is not compounded.
Calculator
Simple interest formula
I = P × (r / 100) × t; A = P + I. P is the starting principal, r is the annual interest rate in percent, t is time in years, I is interest and A is the total amount. Interest is not added to the principal during the term.
About This Calculator
What It Does
This calculator finds simple interest using the original principal, an annual interest rate and a duration in years. It also adds that interest to the principal to show the total amount at the end of the period. The rate is treated as a fixed annual percentage, and the calculation does not compound.
Worked Example
For a principal of 10,000 at 5% per year for 10 years: I = 10,000 × 0.05 × 10 = 5,000. The total amount is 10,000 + 5,000 = 15,000. The displayed currency follows your selected country.
Real-World Usage
Use this estimate to understand a fixed-rate arrangement that calculates interest only on the original principal, or to compare a simple-interest offer with another quote. Check the agreement for fees, payment timing and its definition of the rate.
Local Context
The result is a mathematical estimate, not a lender quote. It assumes the annual rate stays constant for the full term, the principal remains unchanged, and the term can be represented in years. It excludes fees, taxes, inflation and payment schedules. For a term in months, convert months to years before entering it.
Last reviewed: November 2026.
Frequently Asked Questions
How is simple interest calculated?
Multiply the principal by the annual rate as a decimal and by the time in years: I = P × r × t. Add the interest to the principal for the total amount.
Does this calculator compound interest?
No. Interest is calculated only on the original principal; previously earned interest is never added to the base.
What if my term is in months?
Choose months in the term-unit selector; for example, 6 months is half a year.