Simple Interest Calculator
Calculate simple interest with I = P × r × t — interest, total value and the effective yearly take on any principal and rate.
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Currency: Amounts are calculated in the currency you select; this site does not convert between currencies and does not use live exchange rates.
What this tool does
Simple interest charges (or pays) interest only on the original principal, never on accumulated interest — so it grows in a straight line. It is how many car loans, short-term notes and some bonds are quoted, and the baseline against which compound interest shows its advantage.
How to use the Simple Interest Calculator
- Enter your figures in the fields above.
- Check the filing status, state and pay-frequency selections — they change the tables used.
- Read the headline result first, then the breakdown: it shows exactly which tax or amount produced each line.
- Change any input to compare scenarios; the result updates with the same dated tables shown on this page.
Formula
I = P × r × t; total = P + I
- P
- Principal — the starting amount
- r
- Annual rate as a decimal
- t
- Time in years (fractions allowed)
Worked example
$10,000 at 5% simple interest for 3 years earns exactly $1,500 — $500 every year — for a total of $11,500. Compounded annually it would earn $1,576.25.
Inputs
- Principal10000
- Annual interest rate (%)5
- Time (years)3
Result
- Simple interest earned$1,500.00
- Total amount (principal + interest)$11,500.00
- Interest per year$500.00
Results explained
- Simple interest earned
- P × r × t — linear in all three inputs.
- Total amount (principal + interest)
- What you end with (or owe) at the end of the term.
Frequently asked questions
I = P × r × t: principal times the annual rate (as a decimal) times years. $1,000 at 4% for 2 years earns $80.
Simple interest is paid only on the original principal. Compound interest also earns interest on past interest, so it curves upward — over long periods the gap is large.
Short-term loans and notes, many auto loans, some government bonds' coupon math, and late-payment or judgment interest in many jurisdictions.
Enter time as a fraction of a year — 6 months is 0.5, 90 days is about 0.25. The formula only needs t in years.
Almost never — deposit accounts compound (daily or monthly), quoted as APY. Compare with the Effective Interest Rate Calculator.