● Money & small business
What investing $100 to $1,000 a month grows to in 10, 20, 30 and 40 years
✓ TestedWorked example · monthly compounding, checked against the closed-form future-value formula2026-09-28
Regular investing grows in two ways: the money you add, and the returns on everything already there. In the early years the first dominates; later, growth takes over. The table shows both: what you put in, and what it grows to at a steady 5%, 7% or 9% a year (the yearly rate turned into its monthly equivalent, with each month's amount added at the end of the month). For your own numbers, use the compound interest calculator.
What monthly investing grows to
| Each month | For | You put in | At 5% | At 7% | At 9% |
|---|---|---|---|---|---|
| $100 | 10 years | $12,000 | $15,436 | $17,105 | $18,972 |
| $100 | 20 years | $24,000 | $40,580 | $50,754 | $63,885 |
| $100 | 30 years | $36,000 | $81,538 | $116,945 | $170,211 |
| $100 | 40 years | $48,000 | $148,252 | $247,154 | $421,924 |
| $250 | 10 years | $30,000 | $38,591 | $42,763 | $47,430 |
| $250 | 20 years | $60,000 | $101,451 | $126,884 | $159,713 |
| $250 | 30 years | $90,000 | $203,844 | $292,363 | $425,528 |
| $250 | 40 years | $120,000 | $370,631 | $617,886 | $1,054,810 |
| $500 | 10 years | $60,000 | $77,182 | $85,526 | $94,859 |
| $500 | 20 years | $120,000 | $202,902 | $253,768 | $319,426 |
| $500 | 30 years | $180,000 | $407,688 | $584,726 | $851,056 |
| $500 | 40 years | $240,000 | $741,262 | $1,235,771 | $2,109,620 |
| $1,000 | 10 years | $120,000 | $154,363 | $171,052 | $189,719 |
| $1,000 | 20 years | $240,000 | $405,804 | $507,536 | $638,852 |
| $1,000 | 30 years | $360,000 | $815,376 | $1,169,453 | $1,702,113 |
| $1,000 | 40 years | $480,000 | $1,482,525 | $2,471,542 | $4,219,239 |
What the table shows
- Time does more than the amount. $500 a month for 40 years at 7% ($1,235,771) beats $1,000 a month for 30 years ($1,169,453), with $120,000 less put in.
- Growth overtakes contributions. $500 a month at 7% for 30 years: you put in $180,000 and it grows to $584,726, so 69% of the balance is growth.
- The return matters more the longer you go. Over 10 years, 9% instead of 5% adds 23%; over 40 years it nearly triples the result ($2,109,620 vs $741,262 at $500 a month).
Keep in mind
- Returns aren't steady. Real markets swing year to year; a steady rate is a simplification, and the order of good and bad years matters most near the end.
- Inflation. $1,235,771 in 40 years buys much less than today. At 3% inflation it's worth about $379,000 in today's dollars (the calculator shows this if you enter inflation).
- Taxes and fees reduce the return; a 401(k) or IRA can defer or avoid the tax on growth.
Every figure was computed month by month and matches the closed-form future-value formula. Not financial advice. Related: years to financial independence by savings rate.