Compound Interest Calculator
Project investment growth.
Compound Interest Calculator at a glance
Compound Interest Calculator is a free online calculator you can use right now to project investment growth โ no account, no install and no usage limit. It runs entirely inside your browser, so whatever you enter stays on your own device.
- Price
- Free โ no trial, no paid tier, no watermark
- Sign-up
- Not required
- Where it runs
- In your browser โ nothing is uploaded to a server
- Works on
- Chrome, Safari, Firefox and Edge โ desktop, tablet and phone
- Category
- Calculators
About Compound Interest Calculator
The Compound Interest Calculator projects how an investment grows when returns are earned on top of previous returns. Enter your starting amount, rate, time period and compounding frequency to see the final balance and how much of it is interest rather than your own contributions.
The formula is A = P(1 + r/n)^(nt) โ principal, annual rate, compounds per year, and years. What makes compounding powerful isn't the rate so much as the exponent: time is doing most of the work. The same rate over 30 years produces a dramatically different outcome than over 10, and the gap widens the longer you leave it.
A useful mental shortcut is the Rule of 72: divide 72 by your annual rate and you get the rough number of years for the money to double. At 6%, that's about 12 years; at 9%, about 8. It's an approximation, but a good one for quick comparisons.
How to use Compound Interest Calculator
- Type your numbers into the fields.
- The result updates the moment you change a value.
- Adjust any input to compare different scenarios.
Frequently asked questions
How does compounding frequency affect the result?
More frequent compounding earns slightly more, because interest starts earning interest sooner. The jump from annual to monthly is noticeable; from monthly to daily it's marginal โ the rate and the time period matter far more.
What's the difference between simple and compound interest?
Simple interest is calculated only on your original principal. Compound interest is calculated on the principal plus all interest already earned, which is why the growth curve steepens over time.
Does this account for inflation or tax?
No โ these are nominal figures. Real purchasing power grows more slowly than the numbers suggest, and returns may be taxable depending on the account and your country.
What is the Rule of 72?
Divide 72 by your annual return to estimate the years needed to double your money. At 8% that's roughly 9 years. It's approximate but close enough for comparing options.