What happens if you invest $300 a month
Investing $300 a month at an 8% average annual return grows to about $447,108 after 30 years, from just $108,000 of your own money. Here is the full picture.
Growth table: $300 a month
| Time | You put in | At 6% | At 8% | At 10% |
|---|---|---|---|---|
| 5 years | $18,000 | $20,931 | $22,043 | $23,231 |
| 10 years | $36,000 | $49,164 | $54,884 | $61,453 |
| 15 years | $54,000 | $87,246 | $103,811 | $124,341 |
| 20 years | $72,000 | $138,612 | $176,706 | $227,811 |
| 25 years | $90,000 | $207,898 | $285,308 | $398,050 |
| 30 years | $108,000 | $301,355 | $447,108 | $678,146 |
| 35 years | $126,000 | $427,413 | $688,165 | $1,138,991 |
| 40 years | $144,000 | $597,447 | $1,047,302 | $1,897,224 |
Monthly contributions at month end, returns compounded monthly, no taxes or fees. Starting balance $0.
How long until you're a millionaire?
Investing $300 a month from scratch, you would reach $1,000,000 in about 48.0 years at 6%, 39.5 years at 8%, or 33.8 years at 10%.
Why the last decade matters most
Look at the 8% column. Going from 30 to 40 years adds more than the first 20 years combined. That's compounding: in later years, growth on your existing balance far exceeds your contributions. Starting earlier beats investing more later.
Want to add a starting balance or raise your contribution each year? Try the compound interest calculator with $300/month pre-filled.
Where to invest $300 a month
For most people, a low-cost, broadly diversified index fund (a total US market or S&P 500 fund, often paired with an international fund) inside a tax-advantaged account is the simplest place to start. Many brokers let you schedule automatic monthly investments, including fractional shares.
Common questions
How much will $300 a month be worth in 20 years?
About $176,706 at an 8% annual return, $138,612 at 6%, or $227,811 at 10%. You would have contributed $72,000.
Is an 8% return realistic?
The US stock market has returned about 10% a year nominally over the long run, but with big swings and decade-long flat stretches. 6–8% is a common planning assumption for a stock-heavy portfolio.