Simple Interest Calculator

Calculate simple interest and ending amount, or solve for principal, rate, or time using I = P × r × t.

Formula

I = P × r × t. A = P + I. Time converts to years (months ÷ 12, days ÷ 365).

Assumptions

Interest rate is an annual percentage converted to a decimal.
Day counts use a 365-day year basis.

Limitations

Estimates only — not financial advice.
Actual products may use different timing, fees, compounding, and day-count conventions.

Worked example

$10,000 at 5% for 3 years

Interest = $10,000 × 0.05 × 3 = $1,500. Ending amount = $11,500.

Frequently asked questions

What is the difference between simple and compound interest?

Simple interest is calculated only on the principal. Compound interest earns interest on accumulated balance. Use the Compound Interest Calculator for growth projections.

What day-count basis is used for days?

Days are converted using a 365-day year basis unless otherwise noted.

Last reviewed: 2026-07-23

Category: Finance

Results are provided for informational purposes only and may not reflect real-world policies, fees, or individual circumstances.