An investment growth calculator projects what a starting balance plus ongoing contributions could become, assuming a steady average return. It’s the clearest way to picture the long game: small, regular investing turning into a meaningful sum.
The default above — $10,000 to start, $500 a month, 7% a year for 20 years — reflects a broadly diversified portfolio over a long horizon. Change any input to match your own plan.
How investment growth compounds
Your returns get reinvested and start earning returns of their own. Early on, your contributions are the bulk of your balance. But after enough years, growth on past growth takes over — eventually you can earn more in a single year from the market than you contribute, a tipping point the calculator highlights for you.
This is why the growth curve bends upward rather than rising in a straight line. The back half of a long investing horizon does far more work than the front half.
Why regular contributions beat timing
Trying to time the market is famously hard. Contributing a fixed amount on a schedule — dollar-cost averaging — sidesteps the problem: you buy more when prices are low and less when they’re high, and you stay invested through the ups and downs that actually generate the long-run return.
Use the “Add $100/month” and “Double your contribution” what-if chips to see how sensitive your final number is to how much you put in. For most people, contribution size is the lever they control most directly.
Returns, inflation, and being realistic
A 7% long-run return is a reasonable planning assumption for a stock-heavy portfolio, but real markets are bumpy — some years are up 20%, others down. Turn on the “likely range” toggle to bracket your projection, and remember that no calculator predicts the future; it models an average.
Inflation quietly erodes purchasing power, so a six-figure balance decades from now buys less than it sounds. Switch on “in today’s money” to see the inflation-adjusted value — the number that actually reflects what your portfolio could buy.
Frequently asked questions
What is a realistic investment growth rate?
For a diversified stock portfolio, 6–8% a year is a common long-run planning figure after accounting for a typical mix. Individual years vary wildly. Use a conservative rate and the likely-range toggle to avoid over-promising yourself.
How much will my investments grow in 20 years?
It depends on your starting amount, contributions, and return. As an example, $10,000 plus $500 a month at 7% for 20 years grows to roughly $300,000 — and most of that is growth, not the money you put in. Enter your own numbers above.
Should I invest a lump sum or monthly?
Both work. A lump sum invested earlier has more time to compound, while monthly investing spreads out your risk and matches how most people earn. The calculator lets you model a starting amount and a monthly contribution together.
Does this account for inflation?
Yes — toggle “in today’s money” to see the inflation-adjusted value of your projected balance, so you know what it would actually be worth in current purchasing power.