$150 a month for 15 years at returns from 4% to 10%
| Return | Balance | Of which growth | In today’s dollars |
|---|---|---|---|
| 4% | $36,699 | $9,699 | $23,555 |
| 5% | $39,724 | $12,724 | $25,497 |
| 6% | $43,037 | $16,037 | $27,624 |
| 7% | $46,666 | $19,666 | $29,953 |
| 8% | $50,641 | $23,641 | $32,504 |
| 10% | $59,767 | $32,767 | $38,362 |
Year by year at 7%
| Year | Put in so far | Balance | In today’s dollars |
|---|---|---|---|
| 1 | $1,800 | $1,857 | $1,803 |
| 2 | $3,600 | $3,844 | $3,623 |
| 3 | $5,400 | $5,970 | $5,464 |
| 4 | $7,200 | $8,245 | $7,326 |
| 5 | $9,000 | $10,679 | $9,212 |
| 6 | $10,800 | $13,284 | $11,125 |
| 7 | $12,600 | $16,071 | $13,067 |
| 8 | $14,400 | $19,053 | $15,041 |
| 9 | $16,200 | $22,244 | $17,048 |
| 10 | $18,000 | $25,658 | $19,092 |
| 11 | $19,800 | $29,311 | $21,175 |
| 12 | $21,600 | $33,220 | $23,300 |
| 13 | $23,400 | $37,402 | $25,469 |
| 14 | $25,200 | $41,877 | $27,686 |
| 15 | $27,000 | $46,666 | $29,953 |
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 $150 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 | $14,600 | $18,755 | $23,654 |
| 15 years | $30,996 | $44,592 | $63,404 |
The middle of the simulation sits below the steady 7% figure of $46,666 because ups and downs cost compounding: a 20% loss needs a 25% gain to get back.
What $46,666 would pay in retirement
At a 4% first-year withdrawal, $46,666 pays about $1,867 a year, $156 a month, before tax; in today’s dollars that is about $1,198 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.
$1,800 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.
$150 a month for other terms
| Years | Balance | In today’s dollars |
|---|---|---|
| $150 a month for 5 years | $10,679 | $9,212 |
| $150 a month for 10 years | $25,658 | $19,092 |
| 15 years | $46,666 | $29,953 |
| $150 a month for 20 years | $76,130 | $42,152 |
| $150 a month for 25 years | $117,456 | $56,098 |
| $150 a month for 30 years | $175,418 | $72,270 |
| $150 a month for 35 years | $256,712 | $91,231 |
| $150 a month for 40 years | $370,731 | $113,650 |
Other amounts for 15 years
$50 a month: $15,555, $100 a month: $31,110, $200 a month: $62,221, $250 a month: $77,776, $300 a month: $93,331, $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.