About the Investment Calculator
Whether you invest through a 401(k), an IRA, or a taxable brokerage account, the two biggest drivers of long-term growth are how much you contribute and how long your money stays invested. This calculator separates those effects so you can see exactly how much of the final value comes from your own contributions and how much comes from investment growth.
Try different return assumptions to see a range of outcomes. Many people compare a conservative, moderate, and optimistic scenario rather than relying on a single number.
How It Works
The expected annual return is treated as an effective yearly rate and converted to an equivalent monthly rate. Your initial investment grows at that rate for the whole period, and each monthly contribution is invested at the end of the month and grows for the remaining months.
The chart stacks your contributions underneath investment growth, so the gap between the two layers shows how compounding builds on itself over time.
Formula
- Pinitial investment
- Cmonthly contribution
- imonthly return, (1 + R)^(1/12) − 1
- Rexpected annual return as a decimal
- mmonths invested (12 × years)
Example
An investor puts $10,000 into a diversified index fund, adds $500 a month, and assumes a 7% average annual return for 20 years.
Inputs
- Initial investment
- $10,000
- Monthly contribution
- $500
- Expected return
- 7.00%
- Period
- 20 years
Results
- Final portfolio value
- $292,465.03
- Total invested
- $130,000.00
- Investment growth
- $162,465.03
In this scenario, investment growth accounts for about 56% of the final value. Actual market returns vary every year and can be negative.
Understanding Your Results
- Final Portfolio Value: The estimated value of your investments at the end of the period, before taxes, fees, and inflation.
- Total Invested: Your initial investment plus all monthly contributions.
- Investment Growth: The estimated gain from returns on your money.
- Share of Value from Growth: How much of the final value came from growth rather than contributions. It usually rises the longer money stays invested.