Investment Calculator
Enter a starting amount, a monthly contribution, and an expected annual return to project your balance year by year. The chart splits the result into what you put in and what growth added, with the decade milestones in a table underneath.
What's already invested today
Added at the end of each month
7% is a common long-run assumption for diversified stocks
How long the money stays invested
Step up your monthly amount each year, like with raises
Ending balance in 25 years
$462,290
at 7% per year, compounded monthly
Total contributed
$160,000
your starting amount plus every deposit
Total growth
$302,290
65% of the ending balance is growth
Milestones along the way
| Year | You put in | Growth | Balance |
|---|---|---|---|
| 10 | $70,000 | $36,639 | $106,639 |
| 20 | $130,000 | $170,851 | $300,851 |
| 25 | $160,000 | $302,290 | $462,290 |
Growth accelerates late: each decade typically adds more dollars than the one before it, because the gains themselves keep compounding.
How the projection works
Each month the balance grows by one twelfth of your annual return, then your contribution lands on top. That is the textbook future value of a lump sum plus an ordinary annuity, run month by month: FV = P(1 + r/12)^12t for the starting amount, plus the same compounding applied to every deposit for however long it stays invested. If you set an annual contribution increase, the monthly amount steps up once per year, which mirrors how most people actually invest: contributions grow with income. The engine underneath is plain compound interest, gains earning gains, and our guide to how compounding works walks through why the curve bends upward instead of climbing in a straight line.
What the defaults turn into
Start with $10,000, add $500 a month, assume 7% per year, and give it 25 years: the projection lands at about $462,000. You put in $160,000 of that (the starting amount plus 300 deposits), and growth contributes roughly $302,000, so almost two thirds of the ending balance is money the market added rather than money you deposited. The milestone table shows how lopsided the timing is: after 10 years the balance is only around $107,000, after 20 it is about $301,000, and the final five years add over $160,000 on their own. The last stretch always does the heavy lifting, which is the whole argument for starting early and staying put.
Picking a return you can defend
The honest answer is a range, not a number. Long-run averages for broad, diversified stock index funds sit in the high single digits before inflation, roughly 7% after it, but the path there includes years down 30% and years up 30%. A reasonable habit: run the projection at 7%, then again at 5%, and make plans that survive the lower line. Be suspicious of any assumption above 10% held for decades; the calculator will happily draw it, but history rarely has.
Sequence risk and fees while you accumulate
One piece of good news: while you are contributing, the order of returns matters much less than the average, because bad years let your deposits buy in cheaper. Sequence risk becomes a real issue when you start withdrawing, not while you build. What does bite during accumulation is cost. A recurring fee compounds by the same math as your return, just in reverse, and a 1% annual fee can quietly claim a six-figure share of a projection like the one above. The investment fee calculator turns that percentage into a lifetime dollar figure worth seeing once.
Frequently asked questions
What annual return should I use?
Broad, diversified US stock index funds have historically averaged high single digits per year over multi-decade stretches, which is why 7% is such a common planning number. It is an assumption, not a promise: any single year or even decade can land far away from the average. Many people run the calculator twice, once around 7% and once at a more conservative 5%, and plan between the two.
Does this calculator account for inflation?
Not automatically. If you want the ending balance in today's purchasing power, use a lower real return: for example 5% instead of 7% if you assume roughly 2% inflation. The math is identical, only the interpretation changes.
What does the annual contribution increase do?
It raises your monthly contribution once a year by the percentage you set, the way contributions tend to follow raises. It compounds quietly: stepping a $500 monthly contribution up 2% per year turns the default projection's ending balance from about $462,000 into about $541,000 over 25 years.
How does the compounding work here?
The balance grows by one twelfth of the annual return each month, and your contribution is added at the end of the month. That is the same convention most retirement projections use. Annual compounding would produce a slightly smaller number; the gap is small next to the uncertainty in the return itself.
Are investment returns guaranteed?
No. Markets swing, sometimes brutally, and a projection like this one draws a smooth line through what is in reality a jagged ride. Long horizons and steady contributions make the average more likely to show up, but nothing makes it certain. Treat every number on this page as an educational estimate.
Does this calculator save my numbers?
No. Everything runs in your browser and nothing you type is stored or sent anywhere.
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