Calculate simple interest and total amount from principal, rate and time
Simple interest is calculated on the original principal only, for the entire duration of the loan or deposit — unlike compound interest, previously-earned interest never itself earns more interest. This calculator uses the standard formula Interest = P × R × T ÷ 100, where P is the principal, R is the annual interest rate as a percentage, and T is the time in years, then adds that interest back to the principal to give the total amount owed or earned.
Tips: simple interest is common for short-term loans, certain bonds, and some auto loans — if you're comparing against a savings account or credit card that compounds interest, use the separate Compound Interest Calculator instead, since the two will give noticeably different totals over multi-year periods.
Simple interest is calculated only on the original principal for the whole period, so it grows linearly. Compound interest is calculated on the principal plus any interest already accrued, so it grows faster the longer the money is invested or owed. Over short periods the difference is small; over many years it becomes substantial.
Months are converted to years by dividing by 12 before applying the formula, since the rate you enter is an annual rate. For example, 6 months is treated as 0.5 years.
The table only shows when the time period is set to more than one whole year, since a yearly breakdown isn't meaningful for a loan or deposit lasting a year or less.
Yes — the math is the same whether you're earning interest on a deposit or owing interest on a loan. Just keep in mind that most real-world installment loans actually amortize (interest recalculated on a shrinking balance as you make payments) rather than using flat simple interest on the original principal, so treat this as an estimate for loans with regular repayments.
No — every calculation runs locally in your browser using JavaScript. Nothing you enter is transmitted, logged, or stored anywhere.