Calculate simple interest from principal, rate and time in years, months, days or between two dates.
| Year | Interest | Balance |
|---|---|---|
| 1 | $500.00 | $10,500.00 |
| 2 | $1,000.00 | $11,000.00 |
| 3 | $1,500.00 | $11,500.00 |
Formula: Interest = Principal × Rate × Time (days ÷ 365).
Please do not make financial decisions based on these results.
What is the Simple Interest Calculator?
Simple interest is charged only on the original principal, not on accumulated interest. It is common in short-term loans, some bonds and basic interest problems.
How investments grow
Growth depends on how much you invest, how long you stay invested and the rate of return. Because returns compound, time is the most powerful input. Start with the compound interest calculator to see the effect, then use the investment calculator for contributions and taxes.
How to use the Simple Interest Calculator
- Enter your numbers. The inputs are Principal ($), Interest rate (% per year), Years. Use a rate of return you consider realistic; small changes compound into large differences. Fields marked optional can stay at zero.
- Choose your options. Enter the time as… change how the result is worked out, and the form updates to match your choice.
- Read the result. The highlighted box gives the Interest earned, and the cards below show Total amount (principal + interest), Time, Interest per year. Tables and charts break it down further.
- Test other scenarios. Results update as you type. Change one value at a time to see what drives the answer, and press Reset to go back to the defaults.
Formula and how it works
Example with real numbers
Here is the Simple Interest Calculator using the default values shown in the calculator above:
Inputs
| Principal ($) | 10,000 |
|---|---|
| Interest rate (% per year) | 5 |
| Enter the time as… | Years, months & days |
| Years | 3 |
Results
| Interest earned | $1,500.00 |
|---|---|
| Total amount (principal + interest) | $11,500.00 |
| Time | 3 years (1,095 days) |
| Interest per year | $500.00 |
| Interest per month | $41.67 |
With these inputs the calculator returns Interest earned: $1,500.00. Change any value in the calculator to see how the result moves.
What the results tell you
The results panel of the Simple Interest Calculator reports Interest earned, total amount (principal + interest), time, interest per year and interest per month. Compare these figures while changing one input at a time, and use the related calculators below to look at the same situation from another angle.
Tips for better results
Method and limits. This calculator applies the formula in the section above to your inputs, in your browser; nothing you enter is stored on our servers. Investment returns are not guaranteed. The result shows what the numbers you enter would produce, not what the market will do. It is for information, not financial, tax or legal advice.
Frequently asked questions
Can I use dates?
Yes. Choose Start and end dates and the tool counts the days.
How is simple interest different from compound interest?
With simple interest the interest does not earn more interest, so growth is linear instead of exponential.
What rate of return should I assume?
There is no guaranteed rate. Test a range of conservative and optimistic rates, and remember that fees and inflation reduce your real return.
Are investment returns guaranteed?
No. Real returns vary. Use these tools to compare scenarios, not to predict results.
Are the results guaranteed?
No. Results depend entirely on the numbers you enter and the formulas shown on this page. Please do not make financial decisions based on them alone; confirm important figures with a licensed professional.
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