Investment growth calculator projects your portfolio value from initial deposit, contributions, return rate, and compounding over time. Editable rates, no signup.
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Calculation details
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$10k + $500/mo at 8%, 20 yrs
What this means for your numbers: Contributions supply 85% of the worked example's $320,955. Doubling the initial stake adds ~$37,000; doubling the monthly adds ~$274,000. The monthly lever is 7x stronger.
Illustrative breakdown using the worked example above. The calculator computes your own numbers with the same formula.
Where the Number Comes From
The calculator solves the standard future value of a lump sum plus an annuity: FV = P x (1 + r/12)^(12n) + PMT x [((1 + r/12)^(12n) - 1) / (r/12)]. The first term grows your starting balance; the second grows every monthly deposit, assuming each deposit earns the same rate for the months remaining.
Worked example: $10,000 initial, $200/month, 7% annual return, 10 years. The monthly rate is 0.07/12 = 0.0058333 and there are 120 months, so (1.0058333)^120 = 2.009661. The lump sum grows to 10,000 x 2.009661 = $20,097. The annuity factor is (2.009661 - 1) / 0.0058333 = 173.085, so deposits grow to 200 x 173.085 = $34,617. Total: $54,714. You contributed $34,000, meaning growth added $20,714, about 61% of everything you put in.
Notice how much of the total comes from the deposits rather than the starting balance. Stretch the same inputs to 20 years and the deposit term dominates even more, which is why contribution size and time in the market usually matter more than squeezing an extra 0.5% of return.
What a Flat Rate Hides
The 7% you type is applied identically every month. Real portfolios do not work that way. A sequence returning +25%, -15%, and +8% averages about 6% but compounds to only about 14.3%, not 16.99%, because a -15% year needs a +17.6% gain just to break even. Over short windows this sequencing effect can swing results by thousands of dollars; over 30-year horizons it matters less.
Fees compound too. The same $10,000 plus $200/month example at 6% instead of 7% (a 1% annual fee drag) lands at $50,970 after 10 years: $3,744 less, roughly 11 weeks of contributions erased without you doing anything wrong.
The result is also in nominal dollars. At 3% inflation, that $54,714 in 10 years buys about what $40,712 buys today. Finally, the tool assumes no taxes: taxable accounts pay on dividends and gains along the way, so treat the output as a pre-tax ceiling, not a take-home figure.
