Compound Interest Calculator
See how your money grows with compound interest over time.
$144,573
Final Balance
$58,000
Total Contributed
$86,573
Interest Earned
Learn More
Understanding This Calculator
What this calculator does
This calculator shows how an initial investment plus regular monthly contributions grow over time when interest is compounded. It splits your final balance into money you contributed versus interest the account earned, so you can see exactly how much growth came from compounding alone.
How to use the results
- 1.Enter your starting amount (principal) and the amount you plan to add each month.
- 2.Set the annual rate you expect — use 4–6% for conservative savings, 7–10% for a stock-heavy portfolio.
- 3.Pick how often interest compounds (monthly is standard for savings accounts and most investments).
- 4.Read 'Final Balance' as your projected total and 'Interest Earned' as the portion compounding generated.
Worked example
Start with $10,000, add $200/month, earn 7% compounded monthly for 20 years: your balance reaches roughly $143,000. You contributed $58,000; the remaining ~$85,000 is pure compound interest.
Important assumptions & limitations
- •Returns are assumed constant every year — real markets fluctuate, so your results will vary above and below this line.
- •The calculator ignores inflation, taxes, and investment fees, all of which reduce real-world growth.
- •Monthly contributions are assumed to land at the start of each period.
Frequently asked questions
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Mike Starr
Founder, FinanceWizardTools · M.S. Organizational Management