Can I Retire at 40 on $80K? We Ran 5,000 Monte Carlo Paths to Find Out

A 25-year-old earns $80,000 a year, spends $40,000, and invests the rest. That’s a 50% savings rate, which the FIRE rule of thumb says puts financial independence about 17 years away. So: retire at 42, close enough to call it 40.

Plug those exact numbers into our FIRE calculator and the answer comes back differently.

The simple math vs what the simulation actually returns

The 17-year answer assumes a steady 7% real return every single year. Reality doesn’t cooperate that politely. Some years return 25%, some return –30%, and the order matters. So we ran the same scenario through 5,000 Monte Carlo paths, sampling each year’s return from a normal distribution centred on 7% with the historical 15% standard deviation, plus inflation noise.

What came out:

A 68% survival rate sounds high until you flip it around: roughly one in three of those simulated futures runs out of money before life expectancy. That isn’t a hypothetical risk; it’s three coin-flip outcomes out of ten where you’re 75 and broke.

This is also where most FIRE blogs get optimistic. It’s easy to write “with a 50% savings rate you can retire in 17 years” because it’s technically correct on the median. The 32% tail rarely makes it into the headline.

Sequence-of-returns risk is the real story

If you average 7% over 30 years but happen to get –20%, –15%, +5% in your first three retirement years, you’re forced to sell down a depressed portfolio to live on. Those early withdrawals never recover, even when later returns are good. Bengen’s original 4% rule paper (1994) and the Trinity Study both circle around this: average return tells you almost nothing about whether you’ll run out, because withdrawals interact with order-of-returns in a way averages hide.

In our simulation, every “ran out of money” path looks similar. The first five years are below median. The portfolio dips below 80% of starting value by year three. From there it never recovers, even though years 10–25 average above 7%.

Three fixes, ranked by how much they actually help

We re-ran the scenario with one variable changed each time:

• Work two more years (retire at 42). Survival jumps from 68% to 78%. Predictable but blunt.
• Trim retirement expenses by $5K/year. Survival hits 81%. Also predictable; the FIRE number scales with expenses.
• Add $15K/year of part-time income for the first 5 retirement years. Survival reaches 89%. This one is much bigger than it looks.

The third fix is what actual successful early retirees describe. The FIRE community calls it BaristaFIRE; Mr. Money Mustache calls it semi-retirement. The mechanism isn’t that $15K is a lot of money. It’s that it lets the portfolio survive the dangerous opening window without selling at depressed prices. By year six the portfolio has had time to recover, and full withdrawal becomes safe.

The takeaway most FIRE write-ups skip: the cheapest insurance against sequence-of-returns risk isn’t a bigger nest egg. It’s a smaller withdrawal in years 1–5.

Where this scenario doesn’t hold

Worth flagging two big assumptions before you copy this number to your own situation:

• Healthcare in the US. The simulation uses $40K of expenses. If you’re retiring in the US before Medicare, ACA premiums for a household easily add $10–18K/year. That single change drops survival from 68% to around 52% in our runs.
• Dependents. “$40K expenses” assumes one person. The scenario falls apart for a single-income household with kids. Plugging in $65K of expenses keeps the savings rate at 50% only if income rises proportionally — and the math gets a lot uglier.

Run your own version

The exact 68% number is for a very specific person: 25, $80K, $40K, US, no dependents, 7% real return assumption. Yours will be different.

Open the FIRE calculator, drop in your real numbers, and see what your actual probability looks like. The methodology section under the calculator shows you exactly which assumptions to change for your own situation.