Compound Interest Calculator
See how contributions and time compound into real growth.
This tool provides estimates for informational purposes only and is not financial or tax advice.
Final balance
$151,185
Total contributions
$65,000
Total interest earned
$86,185
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How this calculator works
This calculator projects how a starting balance grows when it earns interest and receives regular monthly contributions. Each period, interest is calculated on the current balance - which already includes interest from prior periods - so growth compounds rather than staying linear.
The formula splits time into either monthly or annual periods based on your chosen compounding frequency. In each period, your monthly contribution is added to the balance, and then the balance is multiplied by one plus the periodic rate (the annual rate divided by the number of periods per year).
Total contributions is your starting amount plus every monthly deposit you made. Total interest earned is simply the final balance minus those contributions - the part that came from growth rather than your own deposits. A steeper gap between the two lines on the chart means compounding is doing more of the work.