Simple Interest Calculator

How the estimate works

Enter a principal, an annual interest rate as a percent, and a term in years, months or days (months and days are converted to a fraction of a year, with days assuming a 365-day year). The tool applies the simple interest formula I = P × r × t, where P is the principal, r is the annual rate as a decimal (rate% ÷ 100) and t is the number of years. It instantly shows the estimated interest and the total amount, which is simply the principal plus the interest. Unlike compound interest, simple interest is calculated only on the original principal and never on interest already earned, so it grows in a straight line over time. Values are shown to two decimals for readability while the underlying math stays exact, and plain numbers are used with no currency so you read the result in whatever units you entered.

Estimate only, not financial advice

This is a mathematical estimate that assumes a single fixed rate applied over the whole term with no compounding, fees, taxes or extra payments. Real loans, savings and investments often use compounding or variable rates, so actual figures will differ. Use it to compare scenarios and build intuition, not as a guarantee or a substitute for advice from a qualified financial professional.