Simple Interest Calculator
Simple interest does not add earned interest back to the principal. Figures are informational, not investment advice.
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How to calculate simple interest
- Enter principal and annual rate as a percent.
- Set time in years, months, or days. Days use t = days / 365.
- Interest is principal times rate times time in years.
- For interest that compounds, use the compound interest calculator instead.
Simple interest
Interest on principal only, I = P r t
| Formula | I = P × r × t |
|---|---|
| r | Annual rate as a decimal |
| t | Time in years |
| Compound contrast | Compound interest uses (1 + r/n)^(n t) |
What simple interest is
Simple interest is I = P × r × t with rate as a decimal and time in years. Interest is not added back to earn more interest. Amount is principal plus interest. For compounding use the compound interest calculator.
Years, not a bank day count
Time is a decimal number of years (2.5 is two and a half years). This page does not use 360-day or 365-day bank conventions, and it does not prorate by exact calendar dates.
Not a deposit quote
Savings products that advertise 'simple interest' still may use their own rounding. Figures here are the textbook product. They are not advice. See the disclaimer.
Simple interest questions
Does this page upload what I type?
No. The work runs in the page you opened. CZNull does not receive the input.
Is interest compounded?
No. Use the compound interest calculator for that.
Can I enter months?
Convert to years (6 months is 0.5) or wait for a dedicated month field in a later tool.
Negative rate?
No. Rate must be 0 or greater.
Is this investment advice?
No. It is arithmetic on the numbers you typed.