$100 a month for 40 years at returns from 4% to 10%
| Return | Balance | Of which growth | In today’s dollars |
|---|---|---|---|
| 4% | $116,106 | $68,106 | $35,593 |
| 5% | $148,252 | $100,252 | $45,448 |
| 6% | $190,768 | $142,768 | $58,481 |
| 7% | $247,154 | $199,154 | $75,767 |
| 8% | $322,108 | $274,108 | $98,744 |
| 10% | $555,035 | $507,035 | $170,150 |
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 |
| 5 | $6,000 | $7,120 | $6,141 |
| 10 | $12,000 | $17,105 | $12,728 |
| 15 | $18,000 | $31,110 | $19,969 |
| 20 | $24,000 | $50,754 | $28,101 |
| 25 | $30,000 | $78,304 | $37,399 |
| 30 | $36,000 | $116,945 | $48,180 |
| 35 | $42,000 | $171,141 | $60,821 |
| 40 | $48,000 | $247,154 | $75,767 |
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) |
|---|---|---|---|
| 20 years | $30,636 | $47,404 | $75,277 |
| 40 years | $108,891 | $216,314 | $430,994 |
The middle of the simulation sits below the steady 7% figure of $247,154 because ups and downs cost compounding: a 20% loss needs a 25% gain to get back.
What $247,154 would pay in retirement
At a 4% first-year withdrawal, $247,154 pays about $9,886 a year, $824 a month, before tax; in today’s dollars that is about $3,031 a year. How long a balance near it lasts at each withdrawal: how long $250,000 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 |
| $100 a month for 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 |
| 40 years | $247,154 | $75,767 |
Other amounts for 40 years
$50 a month: $123,577, $150 a month: $370,731, $200 a month: $494,308, $250 a month: $617,886, $300 a month: $741,463, $400 a month: $988,617, $500 a month: $1,235,771, $600 a month: $1,482,925, $750 a month: $1,853,657, $1,000 a month: $2,471,542, $1,500 a month: $3,707,313, $2,000 a month: $4,943,084, $2,500 a month: $6,178,855, $3,000 a month: $7,414,626, $5,000 a month: $12,357,710.
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.