Why is healthcare the biggest wildcard in a FIRE plan?

Healthcare is the hardest line to predict because you typically retire decades before Medicare eligibility at 65, leaving a long gap you must cover yourself. Marketplace (ACA) premiums and out-of-pocket costs vary by state, age, and income, and the rules and subsidies can change between now and when you need them. The flip side is helpful: ACA subsidies are based on your taxable income, and many early retirees living off taxed savings or Roth dollars show low income on paper, which can sharply cut premiums. Still, you should budget generously, keep an HSA funded (2025 limits are $4,300 self / $8,550 family) as a tax-free medical reserve, and model a worst-case year for a major procedure. Treat healthcare as a separate, padded category in your FIRE number rather than folding it into general spending.