The 4% rule (Trinity Study) underpins FIRE math: a portfolio of 25× annual expenses can sustain inflation-adjusted withdrawals for 30+ years. Sub-flavours include Lean FIRE (minimal expenses, ~25× small budget), Fat FIRE (comfortable lifestyle, ~25–33× larger budget), Coast FIRE (enough saved to coast to retirement without further contributions) and Barista FIRE (semi-retirement with part-time income covering living costs).
Critics argue FIRE is achievable mainly by high earners with low expenses, and that retiring at 35 carries 60+ years of sequence-of-returns risk. Proponents counter that financial independence — not necessarily early retirement — is the real goal: the freedom to choose work, not need it.
FIRE Number = Annual Expenses × 25
A household spending CHF 50k per year targets a CHF 1.25m portfolio (25×) to declare financial independence; at a 60% savings rate, they reach the number in about 13 years.