Simple Interest Calculator

I = P × r × t; A = P + I. I is interest and A is principal plus interest, both in the currency shown. P is initial principal in that currency; r is the annual rate as a decimal (enter 5 for 5%, so r = 0.05); t is duration in years.

Enter principal 10,000, annual rate 5%, and 3 years. I = 10,000 × 0.05 × 3 = 1,500.00. The displayed total is 11,500.00. All monetary amounts in this example use $.

Check the arithmetic for a contract that truly applies simple interest to unchanged principal. A repaid loan or recurring deposit needs a cash-flow schedule.

The rate is user supplied, not a market forecast. This model holds principal and rate fixed and excludes compounding, changing balances, payment dates, fees, taxes, and inflation. Actual loan and savings terms can differ. Information only; not financial or legal advice.

• Compound Interest
• Break‑even Calculator
• Percentage Change Calculator

Last reviewed: 2026-09-28.

• OpenStax, Contemporary Mathematics — simple interest
• Consumer Financial Protection Bureau — simple interest teaching guide

Does simple interest earn interest on earlier interest?

No. It applies the entered annual rate to the original principal for the full period.

Can I use this total as my loan payoff amount?

Only if the contract actually uses unchanged principal and simple interest for that term. Repayments, fees and day-count rules can change the payoff.