An investment projection comes down to four numbers — how much you start with, how much you add, how fast it grows and how long you wait — plus the result they produce. This calculator lets you fix any four and solve for the fifth. It is useful for questions like “where will I be in 25 years?”, “how much do I need to invest each month to reach $400,000?” or “what return would I need to get there in 20 years?”.
How to use the investment calculator
- Pick what to solve for: the ending balance, the contribution, the return or the number of years.
- If you are solving for anything other than the balance, enter the target amount.
- Enter your starting amount and, unless you are solving for it, the regular contribution and how often you make it.
- Enter the annual rate of return and the investment length (each is hidden when it is the unknown).
- Choose whether contributions go in at the end or beginning of each period.
The chart stacks your starting amount, cumulative contributions and growth year by year; the table lists the same figures.
The investment growth formula
With an effective annual return R and p contributions a year, the rate per period is r = (1 + R)1/p − 1. The ending balance after n periods is:
Contributions at the start of each period gain one more factor of (1 + r). Solving for PMT or n rearranges this equation algebraically; solving for the rate has no closed form, so the calculator iterates until the balance matches the target to the cent.
Worked example
You have $20,000 invested and add $500 at the end of every month. You assume a 7% average annual return for 25 years.
- Monthly rate: 1.071/12 − 1 = 0.565415%; 300 contributions
- The $20,000 grows to $20,000 × 1.0725 = $108,548.65
- The contributions grow to $391,520.94
- Ending balance: $500,069.59 — $170,000 of your money and $330,069.59 of growth
Now set a $400,000 target and solve for the other unknowns, holding everything else equal:
- Contribution needed: $372.20 a month
- Return needed with $500 a month: 5.643% a year
- Time needed at 7% with $500 a month: 22 years, 3 months
How sensitive is the result to the return?
The same plan — $20,000 up front, $500 a month for 25 years — at different steady returns:
| Annual return | Ending balance | Growth |
|---|---|---|
| 4% | $307,740.79 | $137,740.79 |
| 5% | $360,594.36 | $190,594.36 |
| 6% | $423,981.90 | $253,981.90 |
| 7% | $500,069.59 | $330,069.59 |
| 8% | $591,464.98 | $421,464.98 |
| 9% | $701,304.31 | $531,304.31 |
Every extra percentage point adds 17–19% to the ending balance here, which is why fees and return assumptions deserve as much attention as contribution amounts. Moving the contributions to the start of each month adds about $2,214.
Making the projection realistic
- Use returns after fees. A 1% annual fee turns a 7% portfolio into roughly 6% — see the investment account calculator for the long-run cost.
- Think in today’s dollars. At 2.5% inflation, $500,000 in 25 years buys about what $270,000 does now. The investment inflation calculator does the conversion.
- Expect volatility. Real portfolios zigzag. If you have actual start and end values, the CAGR calculator shows the steady rate they imply.
- Retirement adds a second phase. Saving is only half the plan; the retirement savings calculator also estimates the income your balance can pay once withdrawals begin.
Projections are hypothetical estimates, not financial advice or a guarantee of future returns. Investments can lose value.
Frequently asked questions
What rate of return should I use?
Use a conservative long-run average for the mix you actually hold, after subtracting fees. Diversified stock portfolios have historically averaged more than bonds or cash but with large swings from year to year. Running the calculator at two or three rates gives a range rather than a single promise.
How does the calculator turn an annual return into a monthly one?
It treats the annual return as an effective yearly rate and finds the equivalent monthly rate: (1 + annual)^(1/12) − 1. A 7% year is about 0.5654% a month, so twelve months of growth compound back to exactly 7%.
Can it solve for the return I need?
Yes. Choose 'Return needed to reach a target' and the calculator finds, by numerical iteration, the steady annual return that makes your starting amount and contributions grow to the target in the time you set.
Does the calculator include taxes and inflation?
No. Results are nominal, pre-tax figures. Use the investment inflation calculator to convert them into today's dollars, and remember that taxable accounts owe tax on dividends and realized gains along the way.
Why does my real account not match the projection?
Markets do not deliver a steady return. The order of good and bad years, the timing of your contributions, fees and dividends all change the outcome. A projection is a planning baseline, not a forecast.