$300 a month for 15 years at returns from 4% to 10%
| Return | Balance | Of which growth | In today’s dollars |
|---|---|---|---|
| 4% | $73,397 | $19,397 | $47,111 |
| 5% | $79,447 | $25,447 | $50,994 |
| 6% | $86,074 | $32,074 | $55,247 |
| 7% | $93,331 | $39,331 | $59,906 |
| 8% | $101,282 | $47,282 | $65,009 |
| 10% | $119,533 | $65,533 | $76,724 |
Year by year at 7%
| Year | Put in so far | Balance | In today’s dollars |
|---|---|---|---|
| 1 | $3,600 | $3,714 | $3,606 |
| 2 | $7,200 | $7,688 | $7,247 |
| 3 | $10,800 | $11,940 | $10,927 |
| 4 | $14,400 | $16,490 | $14,651 |
| 5 | $18,000 | $21,359 | $18,424 |
| 6 | $21,600 | $26,568 | $22,250 |
| 7 | $25,200 | $32,142 | $26,134 |
| 8 | $28,800 | $38,106 | $30,081 |
| 9 | $32,400 | $44,487 | $34,096 |
| 10 | $36,000 | $51,316 | $38,184 |
| 11 | $39,600 | $58,622 | $42,350 |
| 12 | $43,200 | $66,439 | $46,599 |
| 13 | $46,800 | $74,804 | $50,938 |
| 14 | $50,400 | $83,755 | $55,372 |
| 15 | $54,000 | $93,331 | $59,906 |
The range in 1,000 simulated markets
A 7% average does not arrive as 7% every year. In 1,000 simulated sequences of returns averaging 7% with 12% volatility, this is where $300 a month ended up: 1 in 10 markets finished below the first figure, half below the middle one, and 1 in 10 above the last.
| After | Weak (1 in 10 lower) | Middle | Strong (1 in 10 higher) |
|---|---|---|---|
| 8 years | $29,200 | $37,511 | $47,309 |
| 15 years | $61,992 | $89,184 | $126,808 |
The middle of the simulation sits below the steady 7% figure of $93,331 because ups and downs cost compounding: a 20% loss needs a 25% gain to get back.
What $93,331 would pay in retirement
At a 4% first-year withdrawal, $93,331 pays about $3,733 a year, $311 a month, before tax; in today’s dollars that is about $2,396 a year. How long a balance near it lasts at each withdrawal: how long $100,000 lasts. To stop saving early and let growth do the rest, see Coast FIRE numbers by age.
$3,600 a year fits in an IRA, whose 2026 limit is $7,500 under 50. See contribution limits, the 401(k) calculator and the Roth IRA calculator.
$300 a month for other terms
| Years | Balance | In today’s dollars |
|---|---|---|
| $300 a month for 5 years | $21,359 | $18,424 |
| $300 a month for 10 years | $51,316 | $38,184 |
| 15 years | $93,331 | $59,906 |
| $300 a month for 20 years | $152,261 | $84,303 |
| $300 a month for 25 years | $234,913 | $112,196 |
| $300 a month for 30 years | $350,836 | $144,540 |
| $300 a month for 35 years | $513,424 | $182,462 |
| $300 a month for 40 years | $741,463 | $227,300 |
Other amounts for 15 years
$50 a month: $15,555, $100 a month: $31,110, $150 a month: $46,666, $200 a month: $62,221, $250 a month: $77,776, $400 a month: $124,442, $500 a month: $155,552, $600 a month: $186,663, $750 a month: $233,329, $1,000 a month: $311,105, $1,500 a month: $466,657, $2,000 a month: $622,210, $2,500 a month: $777,762, $3,000 a month: $933,314, $5,000 a month: $1,555,524.
How it is worked out
Monthly amounts are deposited at the end of each month and compounded monthly at the rate that equals the annual return; lump sums compound once a year. The headline return is 7% a year, the Trinity-style average the site’s retirement pages use; stock-heavy portfolios have averaged more over long periods and bond-heavy ones less, which is why every page shows 4% to 10%. Today’s dollars divide by 3% inflation a year. The range comes from 1,000 simulated sequences of yearly returns averaging 7% with 12% volatility, with each year’s deposits added through the year. Fees and taxes are not taken out. More on the methodology page.