The 4% rule comes from the Trinity study, which modeled 30-year retirements. Retire at 65, fine. Retire at 35 and you're running a portfolio for 50+ years, where a different failure mode dominates: sequence-of-returns risk in your first decade.
Why the first decade eats people
A 1966-style retiree - bad early returns plus inflation - saw the 4% rule fail within 30 years. Stretch to 50 years and the tolerance for early disasters shrinks further. At Firenomics we model this with real historical sequences, and the pattern is consistent: it's rarely the average return that kills a plan, it's the order.
What actually helps (ranked)
- A flexible spending rule - guardrails that cut spending 10% after bad years beat any static rate.
- One year of cash spending outside the portfolio, refilled in good years.
- A variable initial rate: 3.3-3.8% for 50-year horizons instead of 4%.
- Earning any income, even trivial, which mechanically reduces sequence risk.
The uncomfortable summary
FIRE math is mostly about defense. The accumulation phase gets the blog posts; the withdrawal phase is where plans actually die. Model your first 10 years harder than everything else - that's where the risk lives.
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