$100 a month for 15 years at returns from 4% to 10%
| Return | Balance | Of which growth | In today’s dollars |
|---|---|---|---|
| 4% | $24,466 | $6,466 | $15,704 |
| 5% | $26,482 | $8,482 | $16,998 |
| 6% | $28,691 | $10,691 | $18,416 |
| 7% | $31,110 | $13,110 | $19,969 |
| 8% | $33,761 | $15,761 | $21,670 |
| 10% | $39,844 | $21,844 | $25,575 |
Year by year at 7%
| Year | Put in so far | Balance | In today’s dollars |
|---|---|---|---|
| 1 | $1,200 | $1,238 | $1,202 |
| 2 | $2,400 | $2,563 | $2,416 |
| 3 | $3,600 | $3,980 | $3,642 |
| 4 | $4,800 | $5,497 | $4,884 |
| 5 | $6,000 | $7,120 | $6,141 |
| 6 | $7,200 | $8,856 | $7,417 |
| 7 | $8,400 | $10,714 | $8,711 |
| 8 | $9,600 | $12,702 | $10,027 |
| 9 | $10,800 | $14,829 | $11,365 |
| 10 | $12,000 | $17,105 | $12,728 |
| 11 | $13,200 | $19,541 | $14,117 |
| 12 | $14,400 | $22,146 | $15,533 |
| 13 | $15,600 | $24,935 | $16,979 |
| 14 | $16,800 | $27,918 | $18,457 |
| 15 | $18,000 | $31,110 | $19,969 |
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 $100 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 | $9,733 | $12,504 | $15,770 |
| 15 years | $20,664 | $29,728 | $42,269 |
The middle of the simulation sits below the steady 7% figure of $31,110 because ups and downs cost compounding: a 20% loss needs a 25% gain to get back.
What $31,110 would pay in retirement
At a 4% first-year withdrawal, $31,110 pays about $1,244 a year, $104 a month, before tax; in today’s dollars that is about $799 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.
$1,200 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.
$100 a month for other terms
| Years | Balance | In today’s dollars |
|---|---|---|
| $100 a month for 5 years | $7,120 | $6,141 |
| $100 a month for 10 years | $17,105 | $12,728 |
| 15 years | $31,110 | $19,969 |
| $100 a month for 20 years | $50,754 | $28,101 |
| $100 a month for 25 years | $78,304 | $37,399 |
| $100 a month for 30 years | $116,945 | $48,180 |
| $100 a month for 35 years | $171,141 | $60,821 |
| $100 a month for 40 years | $247,154 | $75,767 |
Other amounts for 15 years
$50 a month: $15,555, $150 a month: $46,666, $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.