$400 a month for 15 years at returns from 4% to 10%
| Return | Balance | Of which growth | In today’s dollars |
|---|---|---|---|
| 4% | $97,863 | $25,863 | $62,814 |
| 5% | $105,930 | $33,930 | $67,992 |
| 6% | $114,765 | $42,765 | $73,663 |
| 7% | $124,442 | $52,442 | $79,875 |
| 8% | $135,043 | $63,043 | $86,679 |
| 10% | $159,378 | $87,378 | $102,298 |
Year by year at 7%
| Year | Put in so far | Balance | In today’s dollars |
|---|---|---|---|
| 1 | $4,800 | $4,952 | $4,808 |
| 2 | $9,600 | $10,251 | $9,662 |
| 3 | $14,400 | $15,921 | $14,570 |
| 4 | $19,200 | $21,987 | $19,535 |
| 5 | $24,000 | $28,478 | $24,566 |
| 6 | $28,800 | $35,424 | $29,667 |
| 7 | $33,600 | $42,856 | $34,846 |
| 8 | $38,400 | $50,808 | $40,108 |
| 9 | $43,200 | $59,316 | $45,461 |
| 10 | $48,000 | $68,421 | $50,911 |
| 11 | $52,800 | $78,162 | $56,466 |
| 12 | $57,600 | $88,586 | $62,132 |
| 13 | $62,400 | $99,739 | $67,917 |
| 14 | $67,200 | $111,673 | $73,829 |
| 15 | $72,000 | $124,442 | $79,875 |
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 $400 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 | $38,933 | $50,014 | $63,078 |
| 15 years | $82,656 | $118,912 | $169,077 |
The middle of the simulation sits below the steady 7% figure of $124,442 because ups and downs cost compounding: a 20% loss needs a 25% gain to get back.
What $124,442 would pay in retirement
At a 4% first-year withdrawal, $124,442 pays about $4,978 a year, $415 a month, before tax; in today’s dollars that is about $3,195 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.
$4,800 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.
$400 a month for other terms
| Years | Balance | In today’s dollars |
|---|---|---|
| $400 a month for 5 years | $28,478 | $24,566 |
| $400 a month for 10 years | $68,421 | $50,911 |
| 15 years | $124,442 | $79,875 |
| $400 a month for 20 years | $203,015 | $112,404 |
| $400 a month for 25 years | $313,217 | $149,594 |
| $400 a month for 30 years | $467,781 | $192,720 |
| $400 a month for 35 years | $684,565 | $243,283 |
| $400 a month for 40 years | $988,617 | $303,067 |
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, $300 a month: $93,331, $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.