$200 a month, 40 years, and the magic of compounding.
Long horizons turn small monthly contributions into outsized balances — because growth earns growth. Punch in your numbers and see how much of the final pile is your money vs. compound interest doing its work.
Estimates only. Monthly contributions, monthly compounding, constant return. Real markets vary year to year; assumed return is a long-run average, not a guarantee. Toggle "today's dollars" to see purchasing power — $1M in 40 years buys roughly $307K of today's groceries at 3% inflation.
Each $100K arrives faster than the last.
Investing $10,000/yr at a steady 7%, each $100K milestone arrives faster than the previous. Adjust the dials and watch the bar redistribute.
Annual contribution spread evenly across 12 months, monthly compounding, constant return. Real markets vary.
Every dollar saved today is worth more.
$1 invested at age 30 at a steady 10% becomes — by age 65. Every year of delay shrinks that number — and the cliff is steeper than most people think.
What $1 becomes — and what you'd have to put away monthly to land on $1M by age 65 . Drag the annual return slider above to recalculate.
| Start age | $1 today → | Monthly to $1M |
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Lump sum, constant return, no taxes or fees. The same math drives compound interest everywhere — but framed per-dollar, the cost of delay is harder to ignore.
Most of the final number isn't your money.
With a 40-year horizon and a 7% return, roughly 80% of your final balance is growth — only about 20% is what you actually contributed. Time is the biggest lever you have, and unlike income or returns, it doesn't require a raise or a bull market. It just requires starting.
Compound interest means your earnings start earning earnings of their own. It looks underwhelming for the first decade, then accelerates.
Starting late is expensive.
Try setting "wait" to 10 years with the same monthly contribution and return. The shortfall isn't 10 years' worth of contributions — it's much bigger. The dollars you would have put in early had the most time to compound, so they're the most valuable dollars in the whole pile.
- Years 1–10 contributions look almost flat against growth — boring, easy to dismiss.
- Years 11–25 growth catches up and starts to dominate the bar.
- Years 26+ growth lapping contributions multiple times. This is the part you can't replicate later.
Where this estimate is rough.
- Constant return. Real markets bounce around. 7% is a long-run average for diversified equities, not a yearly guarantee.
- No taxes or fees. Tax-advantaged accounts (401(k), Roth IRA) preserve more of the growth. Taxable accounts lose some to taxes each year.
- No inflation adjustment. A dollar in 40 years buys less than a dollar today. The numbers shown are nominal, not real.
- Contributions held flat. Most people contribute more as their income grows; the calculator doesn't model that.