Compound Interest Calculator — Any Compounding Frequency
What it grows to, what the interest is, and the effective annual rate.
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Short answer
Compound interest can be calculated for free in a web browser from three numbers on one line: the starting amount, the annual interest rate and the number of years. The result is A = P(1 + r/n)^(nt) for the chosen compounding frequency, or A = Pe^(rt) for continuous compounding. Each line also shows the effective annual rate and the simple interest over the same period, which is what makes the size of the compounding effect visible rather than implied.
At a glance
| Accepts | Three numbers per line — amount, annual rate %, years |
|---|---|
| Produces | Final amount, interest, effective rate and simple interest |
| Processing | In your browser |
| Price | Free, no limits |
| Account | Not required |
The compounding frequency is the part a quoted rate usually leaves out, and it is not a rounding error: 12% compounded monthly is 12.6825% a year. The effective annual rate is printed on every line for that reason — it is the one number that makes two differently quoted rates comparable.
Simple interest sits next to it as a baseline. Over one year at a low rate the two are nearly identical; over thirty they are not remotely. The gap between those two rows is the whole of what compounding means, and no single figure shows it.
How to use it
- 1
Type the figures
Three numbers per line: the starting amount, the annual rate as a percentage, then the number of years. For example 10000 5 10.
- 2
Choose the compounding frequency
Annually, half-yearly, quarterly, monthly, daily, or continuously.
- 3
Convert
Each line comes back with the final amount, the interest, the effective annual rate and the simple-interest comparison.
- 4
Copy the result
Copy to the clipboard, or download it as a text file.
Frequently asked questions
What formula does it use?
A = P(1 + r/n)^(nt), where P is the starting amount, r the annual rate as a decimal, n the compounding periods per year and t the number of years. Continuous compounding uses A = Pe^(rt), which is the limit of the same expression as n grows without bound.
What is the effective annual rate?
The rate that would produce the same growth over one year if it compounded only once: (1 + r/n)^n − 1. It is how a 12% rate compounded monthly and a 12.5% rate compounded annually can be compared directly — the first is the more expensive of the two.
Can it include a regular monthly deposit?
No. This works on a single starting amount. Regular contributions are a different formula — an annuity — and would need a fourth number on every line.
Does it work for debt as well as savings?
Yes. The arithmetic does not care which direction the money goes: a card balance left unpaid at 19.9% compounded monthly grows by exactly this formula.
Is tax or inflation accounted for?
No. The figure is nominal — the amount at the end at the rate typed in, with no tax on the interest and no adjustment for what the money will be worth by then.