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What $100 a month for 20 years becomes
Investing $100 a month is about $3.29 a day. Over 20 years you’d contribute $24,000 in total. What it turns into depends on the return:
| Average return | Balance after 20 years | Growth |
|---|---|---|
| 5% (conservative) | $41,103 | $17,103 |
| 7% (≈ stocks after inflation) | $52,093 | $28,093 |
| 8% (our default) | $58,902 | $34,902 |
| 10% (≈ S&P 500 long-run) | $75,937 | $51,937 |
At 8%, every dollar you put in becomes about 2.5 dollars. Notice the shape of the curve: you don’t reach half of the final balance until year 14 — the last 6 years produce as much as the first 14 combined. That is why starting matters more than the amount.
Year by year (8%)
| Year | You put in | Balance |
|---|---|---|
| 2 | $2,400 | $2,593 |
| 4 | $4,800 | $5,635 |
| 6 | $7,200 | $9,203 |
| 8 | $9,600 | $13,387 |
| 10 | $12,000 | $18,295 |
| 12 | $14,400 | $24,051 |
| 14 | $16,800 | $30,802 |
| 16 | $19,200 | $38,721 |
| 18 | $21,600 | $48,009 |
| 20 | $24,000 | $58,902 |
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 20 years?
You would contribute $24,000. At an 8% average annual return, compounded monthly, it grows to about $58,902; at 10% about $75,937; at 5% about $41,103.
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 30 years instead of 20?
At the same 8% average return it grows to about $149,036, from $36,000 contributed. The extra 10 years add about $90,134, 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.