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What $100 a month for 40 years becomes
Investing $100 a month is about $3.29 a day. Over 40 years you’d contribute $48,000 in total. What it turns into depends on the return:
| Average return | Balance after 40 years | Growth |
|---|---|---|
| 5% (conservative) | $152,602 | $104,602 |
| 7% (≈ stocks after inflation) | $262,481 | $214,481 |
| 8% (our default) | $349,101 | $301,101 |
| 10% (≈ S&P 500 long-run) | $632,408 | $584,408 |
At 8%, every dollar you put in becomes about 7.3 dollars. Notice the shape of the curve: you don’t reach half of the final balance until year 32 — the last 8 years produce as much as the first 32 combined. That is why starting matters more than the amount.
Year by year (8%)
| Year | You put in | Balance |
|---|---|---|
| 5 | $6,000 | $7,348 |
| 10 | $12,000 | $18,295 |
| 15 | $18,000 | $34,604 |
| 20 | $24,000 | $58,902 |
| 25 | $30,000 | $95,103 |
| 30 | $36,000 | $149,036 |
| 35 | $42,000 | $229,388 |
| 40 | $48,000 | $349,101 |
Assumes contributions at the end of each month, monthly compounding and a constant return; ignores taxes, fees and inflation. Educational estimates, not advice.
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Open calculator →Questions people ask
How much is $100 a month for 40 years?
You would contribute $48,000. At an 8% average annual return, compounded monthly, it grows to about $349,101; at 10% about $632,408; at 5% about $152,602.
Is 8% a realistic return for $100 a month?
It is close to the long-run average of a broad US stock index fund including dividends (about 10% before inflation, 7% after). Real returns swing widely year to year; use the calculator to test other rates.
What if I invest $100 a month for 50 years instead of 40?
At the same 8% average return it grows to about $793,173, from $60,000 contributed. The extra 10 years add about $444,072, because growth starts earning growth.
How long does $100 a month take to reach $1 million?
About 53 years at an 8% average annual return, starting from zero. Hypothetical, not guaranteed; real returns vary year to year.