Watch a monthly habit grow
Put in a starting amount, add something each month, and see what it becomes. The surprising part is rarely what you save. It's how much the growth adds on top.
Compound growth
Move any slider. No signup, nothing stored.
In 25 years you could have
$271,649
of that is growth: money your money earned.
Balance Money you put in
- Money you put in
- $95,000
- Growth from returns
- $176,649
- Years for money to double at this return
- 9.9
An estimate at a constant return, which real investments never deliver. Saving for retirement in particular? The retirement projection adds your age, retirement date and inflation.
When you pass each milestone
At the numbers above. Add five years or one point of return and watch how far the later milestones move.
Why it works this way
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Your money earns money
Invest $1,000 and it earns, say, $70 in a year. The next year you earn a return on $1,070, not just the original $1,000. The growth starts growing too, which is why the curve bends upward instead of running straight.
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Time matters more than the amount
Save $200 a month from 25 to 65 at 7% and you end with about $525,000. Save twice as much, $400 a month, from 40 to 65 and you end with about $324,000, despite putting in $24,000 more. The extra fifteen years of compounding outweigh the bigger contributions.
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The rule of 72
Divide 72 by the yearly return to estimate how many years money takes to double. At 7%, about 10 years; at 9%, about 8. It's a back-of-the-napkin rule, close enough to be useful, and it makes the value of a slightly higher return, or a slightly lower fee, easy to feel.
Common questions
What return rate should I use?
It depends what you're invested in. From 1928 through 2025, the S&P 500 with dividends reinvested compounded at about 10.0% a year before inflation (Aswath Damodaran, NYU Stern, data updated January 2026), or about 6.8% a year after inflation as measured by the BLS consumer price index. That is why our default is 7%, a round number close to the real figure. That history includes the Depression, the 1970s and 2008, and a single 98-year average says little about the next 25 years. Bonds have returned less, and savings accounts less still. For a cautious projection, try 5% or 6%. Nobody knows the future, so run it a few ways.
Is the final number guaranteed?
No. This is a projection at a steady return every year, and real markets don't move that way: they rise a lot, fall sometimes and go sideways often. Your result will be bumpier than the smooth curve, and could land well above or below it. Treat the calculator as a guide to the shape of things, not a promise.
Does this assume I add money monthly or once a year?
Monthly. The calculator adds your contribution at the end of each month and compounds the balance monthly, which matches how most people save: a little from each paycheck. A once-a-year lump sum gives a slightly different result, but not different enough to change a decision.
Where should the money go?
This calculator shows the math, not the account. Long-term money usually goes into tax-advantaged accounts first: a 401(k), at least up to any employer match, then an IRA, before a taxable brokerage account. Our guide to starting to invest with $1,000 walks through the order.
Does inflation affect these numbers?
Yes. $1 million in 30 years will buy less than $1 million buys today. The simplest fix is to use a return with inflation already taken out. For U.S. stocks since 1928 that has been roughly 7% instead of 10%. Use the "real" figure and the result is in today's purchasing power, which is easier to make sense of.
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This calculator produces estimates at a constant annual return, which real investments do not provide. It is educational and is not personalized investment, tax or legal advice. Past market performance does not guarantee future results.