Simple Interest Calculator
Interest calculated on the principal only, without compounding.
Your figures
Result
How to use this tool
- Enter your own figures over the defaults — Principal, Annual rate, Years.
- The answer updates as you type. There is no button, and nothing is sent anywhere.
- Change Annual rate on its own to see how much it moves the result — the worked example below shows exactly that.
Simple interest is used in some short-term loans and fixed deposits. Over long periods it produces dramatically less than compound interest on the same rate.
How it works
This takes 3 inputs — principal, annual rate, years — and returns interest earned and final amount. The whole calculation happens in this page as you type: there is no submit button, no request, and nothing stored.
Because it recalculates on every keystroke you can use it as a sensitivity test rather than a one-shot answer. Moving annual rate alone from 5 to 6 changes interest earned from 2,500.00 to 3,000.00 — the worked example below sets that out in full.
A worked example
Worked through with the figures the page already has in it: principal of 10,000 and annual rate of 5 %, and the rest as shown, giving interest earned of 2,500.00. These numbers come from running the calculator’s own code, not from being typed in here, so they cannot drift away from what you see on screen.
Starting from:
- Principal: 10,000
- Annual rate: 5 %
- Years: 5 years
| Result | Value |
|---|---|
| Interest earned | 2,500.00 |
| Final amount | 12,500.00 |
What happens when one input moves
Holding everything else steady and changing Annual rate from 5 % to 6 % — one percentage point — moves the answer like this:
| Figure | 5 % | 6 % |
|---|---|---|
| Interest earned | 2,500.00 | 3,000.00 |
| Final amount | 12,500.00 | 13,000.00 |
That is usually the number worth arguing over: it is easier to move than the headline amount, and the difference compounds across the whole term.
Simple Interest Calculator — frequently asked questions
When is simple interest used?
Some short-term personal loans, certain bonds, and a number of fixed deposit products. Most savings and investment products compound.
How different is it from compound interest?
At 5% over 20 years, simple interest doubles your money while compound interest nearly triples it.
What is the formula?
Interest = Principal × Rate × Time, with rate as a decimal and time in years.
Is this calculator free?
Yes, with no account, no limits and no data collection. It runs entirely in your browser.
Should I rely on this for a financial or medical decision?
No. It is a planning estimate built on standard formulas and stated assumptions. For decisions that matter, speak to a qualified professional who can account for your full circumstances.
How accurate is the Simple Interest figure?
The arithmetic is exact. With the defaults on this page — principal 10000, annual rate 5 %, years 5 years — it returns interest earned of 2,500.00. What limits accuracy is the assumptions, not the maths: change annual rate to 6 % and the same formula gives 3,000.00. Treat it as a well-founded estimate, not a quotation.
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Background reading: Loan, Mortgage and Investment Calculators Explained
Nothing is sent anywhere. The figures you type stay in this page and are never transmitted or stored — how that works.
Disclaimer. The formula is exact; the answer is only as good as the figures and assumptions above. Not financial, tax, medical or legal advice. Full disclaimer.