Investment calculator
Explore how an initial investment and regular monthly contributions could grow over time. Change the assumed annual return and number of years to compare your own scenarios.
Edit any line below. Results update as you type. Use the same currency for all monetary amounts.
| @1 | initial = 10000 | |
| @2 | monthlyContribution = 200 | |
| @3 | annualReturn = 5% | |
| @4 | years = 20 | |
| @5 | months = years * 12 | |
| @6 | monthlyRate = annualReturn / 12 | |
| @7 | growth = (1 + monthlyRate) ^ months | |
| @8 | futureValue = monthlyRate == 0 ? initial + monthlyContribution * months : initial * growth + monthlyContribution * (growth - 1) / monthlyRate | |
| @9 | contributions = initial + monthlyContribution * months | |
| @10 | gain = futureValue - contributions |
How compound investment growth works
The starting balance compounds each month. Monthly contributions are added at the end of each month, so earlier contributions have more time to grow. Total contributions include the initial balance and every monthly deposit; the estimated gain is the future value minus those contributions.
Assumptions and limits
The annual return is a hypothetical nominal rate divided by 12, with monthly compounding. Returns are not guaranteed or constant in practice. This estimate excludes fees, taxes, and inflation. Use a positive time horizon and an annual rate greater than -1200% so the monthly growth factor remains positive.
What happens if the return is zero?
With a zero return, the future value equals the initial balance plus all monthly contributions. The worksheet handles this case without dividing by zero.
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