What is an HSA for FIRE? A Health Savings Account (HSA) used for FIRE is a triple-tax-advantaged investment vehicle, tax-deductible contributions, tax-free growth, and tax-free withdrawals for medical expenses, that FIRE practitioners treat as a stealth retirement account by paying current medical bills out of pocket and letting the HSA compound for decades.
Worked example: contribute the 2025 family limit of $8,550/year from age 30 to age 60. Invest the balance in a low-cost index fund at 7% real return. Ending balance: ~$870,000, all tax-free for medical expenses. Save receipts along the way, you can reimburse yourself decades later for any qualified medical expense incurred since the HSA was opened, effectively turning the HSA into a tax-free brokerage account with a delay.
After age 65, HSA withdrawals for non-medical use are taxed as ordinary income (like a Traditional IRA) with no penalty, so the HSA can also function as a bonus retirement account. Requirement: you must be enrolled in an HSA-eligible High Deductible Health Plan (HDHP) to contribute.