Calculator
Compound Interest Calculator
Compound interest is interest earned on both the original balance and interest already credited. Choose a starting amount, monthly contributions, a nominal annual rate, and how often interest compounds.
Investment details
Results
Final balance
$196,665.39
Total contributions
$82,000.00
Total interest earned
$114,665.39
Estimated growth
Yearly illustration of contributions versus estimated balance. This is not a market forecast.
Calculators and articles on this site are for education only. They are not financial, investment, tax, legal, or professional advice.
How this calculation works
Compound interest is interest calculated on both principal and previously earned interest. This tool converts your chosen compounding frequency into an equivalent monthly rate so monthly contributions stay on a consistent timeline.
The result is an illustration at a constant rate. Bank products may quote a compounding APY. Investment accounts do not grow at a fixed rate, so treat market-style inputs as a scenario, not a forecast.
A = P(1 + r/n)^(n t) plus the future value of monthly contributions
P is the starting amount, r is the annual rate, n is compounding periods per year, and t is years. Contributions are modeled monthly using an equivalent monthly rate.
Example
Start with $10,000, add $300 a month, assume 7% a year compounded monthly, and wait 20 years. Contributions total $82,000. The estimated ending balance is higher because interest is credited along the way. Changing the rate or the timeline moves the ending value quickly.
Frequently asked questions
Is the rate a guaranteed return?
No. Some bank products quote a compounding rate; investment returns vary. This tool assumes a constant rate so you can see the math—not future performance.
When are contributions added?
Contributions are treated as monthly. Your compounding frequency is converted to an equivalent monthly rate so the timeline stays consistent.
Why does compounding frequency barely change the result?
At the same nominal annual rate, switching from monthly to daily compounding usually adds only a small amount. Time, contributions, and the rate matter more.
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