Calculators
Compound Interest Calculator
Calculate how savings or investments grow with compound interest and monthly contributions, with a year-by-year table.
- Runs in your browser
- Nothing uploaded
The tool
Enter your numbers below. Results update as you type, and nothing leaves your browser.
Everything you enter stays on your own machine. Nothing is sent to us or to anyone else, which you can confirm in your browser network tab.
What people use it for
- Projecting savings or investment growth
- Comparing compounding frequencies
- Showing the power of starting early
- Financial education
About this tool
What the Compound Interest Calculator does
Compound interest earns interest on previous interest, so growth accelerates over time. This calculator compounds an initial amount and monthly contributions at your chosen frequency and shows how much of the final balance came from contributions and how much from interest.
Formula
- Monthly rate = (1 + annual rate ÷ n)^(n ÷ 12) − 1, where n = compounding periods per year
- Each month: balance = balance × (1 + monthly rate) + contribution
- APY = (1 + annual rate ÷ n)^n − 1
Worked example
Using the starting values in the calculator above:
| Input | Value |
|---|---|
| Initial amount | $10,000 |
| Monthly contribution | $200 |
| Annual interest rate | 7% |
| Years | 20 |
| Compounding | Monthly |
| Result | Value |
|---|---|
| Final balance | $144,573 |
| Interest earned | $86,573 |
| Total contributed | $58,000 |
| Effective annual yield (APY) | 7.23% |
How to read the result
Time matters more than rate. Starting ten years earlier often beats a higher return started later.
Returns from investments vary year to year; a steady rate is a planning assumption, not a promise.
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Questions
Questions about this tool
The things clients actually want to know — costs, timelines, ownership and what happens after launch.
Interest calculated on the original amount plus interest already earned, so the balance grows faster over time.
It depends on the account: daily, monthly, quarterly or annually. More frequent compounding gives a slightly higher effective yield.
Divide 72 by the annual rate to estimate how many years money takes to double. At 7%, about 10 years.
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