Simple Interest Calculator (I = P·r·t)

Compute interest and total amount from principal, annual rate, and time. Private by design—everything runs locally in your browser.

Enter your values

Currency

Principal amount Starting balance (P)

Annual interest rate (%) APR as a percent (e.g., 5 = 5%)

Time

Formula expects years; months/days are converted automatically.

Shortcuts: Enter to calculate • Esc to clear.

Simple interest grows linearly with time. It’s common in short-term loans and some bonds.

Interest: \(I = P\cdot r \cdot t\)
Total amount: \(A = P(1+rt)\)
\(P\) = principal, \(r\) = annual rate as a decimal (5% → 0.05), \(t\) = time in years

Tip: 18 months = 1.5 years; 90 days ≈ 90/365 years (actual day count can vary by contract).

Simple interest uses \(I = P\cdot r \cdot t\) where \(P\) = principal, \(r\) = annual rate (decimal), \(t\) = years. The total is \(A = P(1+rt)\).

No—this tool uses simple interest only. For compounding, try our Compound Interest Calculator.

Yes. Everything runs in your browser—no uploads, no accounts.

Enter years directly, or choose months/days and we’ll convert to years automatically (months ÷ 12; days ÷ 365).