Beyond using an HSA for current medical expenses, what is the most powerful long-term strategy for HSA funds?

The most powerful HSA strategy is to treat it as a stealth retirement account rather than a healthcare checking account. By paying current medical bills out of pocket and investing all HSA contributions in index funds, you allow the balance to compound tax-free over decades. After age 65, HSA withdrawals for non-medical expenses are taxed at ordinary income rates (making them function like a traditional IRA), but withdrawals for qualified medical expenses remain completely tax-free forever. Fidelity estimates that a 65-year-old couple retiring today will need approximately $315,000 for healthcare costs in retirement.