Portfolio size needed for Financial Independence Retire Early

What FIRE actually is

FIRE — Financial Independence, Retire Early — is the idea that if you save enough of your income, at some point your investments can cover your living costs and paid work becomes optional. The core maths is uncomplicated: save a high percentage of your income, invest the savings for long-term growth, stop working when the pot hits 25 times your annual expenses. The complication is in the inputs. Small differences in savings rate or return assumption produce enormous differences in the timeline.

The savings-rate table that changes minds

Here's the result most FIRE explanations build around. Assume 7% real returns, 4% withdrawal rate, and a 25x target. These are the years to financial independence by savings rate:

10% saved → 51 years to FI
20% saved → 37 years
30% saved → 28 years
40% saved → 22 years
50% saved → 17 years
60% saved → 12.5 years
70% saved → 8.5 years

Starting from 0 with a 10% savings rate, you work 51 years. At 50%, it's 17. The non-linearity is the point: halving your spending doesn't halve your working life; it cuts it by two-thirds. The reason is that spending less both increases contributions and reduces the target (25x a smaller number). Both effects compound.

The four FIRE variants

Lean FIRE: a target of around 20,000–25,000 annual spending, requiring a pot of 500k–625k. Feasible on a single income with deliberate frugality; requires accepting a modest lifestyle permanently.

Regular FIRE: 35,000–50,000 annual spending, 875k–1.25m pot. Closest to "retirement as it's typically understood, just 15+ years earlier".

Fat FIRE: 75,000+ annual spending, 1.9m+ pot. Requires high income through the accumulation phase; typically tech, finance, or senior professional careers with disciplined saving.

Coast FIRE: save aggressively in your 20s and 30s until the pot is large enough to grow to your full target without additional contributions. Then work for current expenses only. Less stressful than regular FIRE; requires early discipline.

The savings-rate question is the income question

FIRE calculators focus on savings rate, but the bigger lever for most people is income. Going from 30% savings rate on 40,000 to 30% savings rate on 60,000 cuts the timeline by roughly 5 years because the contributions are larger AND the reduced proportional need (inflation doesn't hit your target as hard) compounds. High-income FIRE — doctors, software engineers, lawyers — often works in 10–15 years not because of extreme frugality but because the absolute contribution amounts are large. Low-income FIRE requires either long timelines or lean-FIRE-level spending discipline.

The problem with the 4% assumption

FIRE's 25x target relies on the 4% withdrawal rule from the Trinity Study. That's a 30-year planning horizon. But FIRE retirees at 40 need their pot to last 50+ years, not 30. Research since the original study suggests safe withdrawal rates for 50-year retirements drop to 3.3–3.5%. That changes 25x into 28–30x — meaningfully more, especially at high spending levels. Many experienced FIRE planners use 3.5% and 30x rather than the popularised 4% and 25x.

Sequence-of-returns risk hits early retirees hardest

The first 5–10 years of a 50-year retirement are the danger zone. A 30% market crash in year two is devastating because your pot hasn't had time to grow beyond the starting figure. Early retirees manage this with a cash buffer (2–3 years of expenses in liquid savings) or a "bond tent" that holds higher fixed-income allocations early and shifts equity-heavy later. The calculator above assumes smooth withdrawals; real plans need a volatility plan on top.

What FIRE calculators don't model

Health costs are the big one. public healthcare access is a huge structural advantage for FIRE; for FIRE, pre-public healthcare health insurance (ages 40–65) often runs 15k–25k annually and reshapes the pot requirement entirely. Life events — divorce, children's education, parental care, health issues — can push spending above the planned base. Most FIRE plans survive first contact with real life only with a cushion built in above the calculator's baseline figure.

The one-more-year problem

When you hit your FIRE number, you may not actually stop. This is a documented pattern: "one more year syndrome". The thought process — "if I work one more year the pot is 7% bigger and I have a bigger safety margin" — is reasonable in the moment but self-perpetuating. Deciding in advance what threshold you'll actually pull the trigger, and writing it down before you get close to it, is the single most useful thing FIRE planners do. The calculator gives you the number; the psychology of acting on it is a separate problem.