Simple Interest Calculator
Global Finance
Simple interest calculator
Enter a principal amount, annual interest rate, and time period to calculate interest earned and total amount.
Simple Interest
Interest
$50.00
Total amount
$1,050.00
Annual rate
5%
How calculations work
All calculations run locally in your browser; we do not call any external APIs.
- Principal: the starting amount you enter.
- Rate: annual percentage rate (entered as %).
- Time: years the principal is invested or borrowed for.
- Interest: computed as Principal × Rate × Time.
- Total: Principal + Interest.
Values are numeric and rounded for display; this is a simple, non-compounding estimate for educational use.
What this calculator does
The Simple Interest Calculator computes interest on a principal amount using a fixed annual rate and a set number of years. Unlike compound interest, simple interest does not reinvest interest; it is useful for short-term or straightforward interest estimates.
Who should use this calculator
Use this when you need a quick, no-frills estimate — for example short-term loans, basic interest on promissory notes, or educational examples. If your situation involves reinvested earnings, use the compound interest calculator instead.
How this calculator works
The formula used is Interest = Principal × Rate × Time (with rate as a decimal). The total amount is Principal + Interest. Inputs are treated as numeric and the rate is interpreted as an annual percentage. All calculations run locally in your browser — no data is sent to any server.
How to interpret the results
The output shows the interest earned over the period and the resulting total. Use different inputs to compare scenarios or to back-calculate a required rate or time to meet a target amount.
Example
For a $2,000 principal at 4% for 3 years, simple interest is $240 and the total is $2,240. This illustrates how simple interest compares to compound returns over short horizons.
Limitations & disclaimer
This tool assumes constant rates and ignores compounding, taxes and fees. It is for informational use only. See the calculators hub for other calculators and localised formats.
Frequently asked questions
What is the difference between simple and compound interest?
Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus previously earned interest. Over time, compound interest grows faster because of this "interest on interest" effect.
When is simple interest used in practice?
Simple interest is common in short-term personal loans, promissory notes, some auto loans, and certain government bonds. It is also used in education to teach the fundamentals of interest calculations.
Can I enter a monthly rate instead of annual?
The calculator expects an annual percentage rate. If you have a monthly rate, multiply it by 12 to convert to annual before entering it.
Does this account for taxes or fees?
No. The calculator shows gross interest before taxes or fees. For net returns, subtract any applicable taxes or charges from the total.
How do I compare this with compound interest?
Use both this calculator and the compound interest calculator with the same principal, rate, and time. The difference shows the extra earnings from compounding.