Investment Calculator
Use this investment calculator to estimate how an investment plan could grow over time from money you invest today and the amount you keep adding each month.
It is built for practical planning: compare contribution levels, test different return assumptions, and estimate a projected ending balance with a clear split between what you contributed and what the estimate attributes to growth.
If you want a more mechanics-first future value view, compare it with the Compound Interest Calculator.
Results are planning estimates only and do not include taxes, fees, inflation, or changing market returns.
How to use this calculator
- Enter the amount you can invest today, or use
$0if you are starting with monthly investing only. - Add the amount you expect to invest each month.
- Choose an annual return assumption that matches the type of account or portfolio you want to model.
- Select how often returns compound and enter the number of years you plan to stay invested.
- Review the projected balance, how much of that total came from your own contributions, and how much came from estimated growth.
This is useful for testing tradeoffs like investing more each month, staying invested longer, or using a more conservative return assumption.
When comparing scenarios, pay the closest attention to three levers: investment period, monthly contribution, and expected annual return. Small changes in any of those can materially change the long-term projection.
How it works
This calculator uses a steady-growth estimate to project how your starting amount and monthly investing could build over time.
It combines growth on your starting balance with growth on each monthly contribution, with the annual return and compounding frequency translated into the monthly rate used in the projection.
Readable projection formula
Projected balance = P × (1 + i)m + PMT × ((1 + i)m − 1) / i
Main inputs in the estimate
- P
- Your initial investment, or the amount you start with today
- PMT
- Your monthly contribution, added regularly throughout the plan
- i
- The monthly-equivalent growth rate based on your expected annual return and chosen compounding frequency
- m
- The total number of months in your investment period
What the estimate assumes
- This formula is a simplified readable representation of the projection logic, using i as the monthly-equivalent rate for clarity.
- When you choose quarterly or annual compounding, the calculator converts that rate into an equivalent monthly growth rate so monthly contributions can be projected consistently.
- Your monthly contributions are added consistently throughout the full time horizon.
- The annual return you enter is treated as a steady average, not a year-by-year market forecast.
- Taxes, fees, inflation, and market volatility are not included.
Assumptions and limitations
- Results are estimates based on a fixed annual return assumption over the full investment period.
- Monthly contributions are modeled as equal deposits made throughout the plan.
- Taxes, fees, inflation, and changing market returns are not included.
- This calculator does not model withdrawals, contribution increases, or account-specific rules.
Example scenario
Use this example to see how a steady investing habit can build long-term value, even without a large lump sum up front.
- Initial investment:
$5,000 - Monthly contribution:
$400 - Expected annual return:
8% - Compounding frequency:
Monthly - Investment period:
25 years
With those assumptions, the projected ending balance is $417,111.44.
That total includes $125,000 of your own contributions and about $292,111.44 in estimated earnings.
This example highlights the planning value of the calculator: it helps you see how regular investing, time in the market, and return assumptions work together to shape a future balance.
Frequently asked questions
Is this calculator guaranteed to predict real investment returns?
No. This calculator provides a planning estimate based on a steady assumed return. Real market performance can be higher or lower, and actual returns will vary from year to year.
Does this investment calculator include inflation?
No. Results are shown in nominal dollars and do not adjust for future inflation or changes in purchasing power.
Are taxes or fees included?
No. The projection does not include taxes, fund expense ratios, advisory fees, trading costs, or account-specific charges.
What annual return should I use?
Use a rate that fits the type of investment you are modeling and how conservative you want to be. Many people test a few scenarios instead of relying on a single return assumption.
Can I use this for index fund investing?
Yes. It can be used for index fund planning, retirement investing, brokerage account estimates, or other long-term investing scenarios, as long as you treat the return as an assumption rather than a promise.
What if I start with $0?
That is fine. Leave the initial investment at $0 and use the monthly contribution field to model building your balance over time from recurring investing alone.
Why could my real results differ from the estimate?
Real results can differ because of market volatility, uneven annual returns, skipped contributions, different contribution timing, taxes, fees, and investment behavior over time. If you want a more mechanics-only comparison, review the Compound Interest Calculator.
Related Calculators
Compound Interest Calculator
Estimate how savings or investments may grow over time from a starting balance, monthly contributions, and compound growth.
Retirement Savings Calculator
Estimate how much you could have saved by retirement based on your age, current retirement savings, monthly contributions, and expected annual return.