What Is Personal FinanceTwo account types let US employees set aside pre-tax money for medical costs, an HSA and an FSA, and it's easy to assume they're interchangeable since both start with "tax-advantaged account for health expenses." They're not. The differences between them, especially what happens to unused money, matter more than the similarities. For the broader health insurance terms these accounts pair with, see health insurance basics.
The HSA: a triple tax advantage
A Health Savings Account (HSA) is only available to people enrolled in a qualifying high-deductible health plan. In exchange for that eligibility requirement, an HSA offers what's often called a triple tax advantage:
- Contributions reduce your taxable income for the year, similar to a traditional retirement account.
- Growth inside the account isn't taxed while the money sits there.
- Withdrawals for qualified medical expenses come out tax-free too, so the money never gets taxed at any stage if used correctly.
Two features set an HSA apart from most tax-advantaged accounts. First, the balance rolls over every year with no expiration and no use-it-or-lose-it deadline. Second, many HSA providers let you invest the balance once it crosses a certain threshold, similar to a retirement account, rather than leaving it sitting in cash. An HSA also stays with you if you change jobs or health plans, since it's owned by you, not your employer.
The FSA: pre-tax, but typically use-it-or-lose-it
A Flexible Spending Account (FSA) also lets you set aside pre-tax money for medical expenses, and contributions reduce your taxable income the same way an HSA's do. The structure diverges from there. An FSA is set up and owned through your employer, and it typically follows a use-it-or-lose-it rule: money left unspent by the end of the plan year is often forfeited, sometimes with a small grace period or limited carryover allowed depending on the specific plan.
Because an FSA doesn't require a high-deductible health plan to qualify, it's available to more employees than an HSA, but the tradeoff is losing unused funds and losing the account entirely if you leave the employer, unlike an HSA's portability.
Choosing between them (when you have a choice)
Most employees don't get a free choice between an HSA and an FSA, since HSA eligibility depends on being enrolled in a high-deductible health plan in the first place. If your employer offers both types of plans, the choice becomes part of a bigger decision about premium, deductible, and expected medical costs for the year, not only the savings account attached to it. Someone who expects low medical costs and wants a long-term, investable account tends to lean toward an HSA-eligible plan. Someone who wants lower out-of-pocket costs during the year and doesn't mind the use-it-or-lose-it structure tends to lean toward a traditional plan paired with an FSA instead.
Estimating next year's medical expenses before enrollment season matters more for an FSA than an HSA, precisely because unspent FSA money disappears at year's end while unspent HSA money doesn't.
Putting it together
An HSA functions closer to a retirement account with a medical-expense angle, built to carry a balance forward and grow over years. An FSA functions closer to a budgeting tool for the year ahead, built to spend down rather than accumulate. Knowing which one you're enrolling in, and what happens to leftover money, changes how you should think about contribution amounts each year.
Nothing here is tax advice. HSA and FSA contribution limits, eligibility rules, and carryover allowances change over time and depend on your specific plan. Check irs.gov or your plan documents for current rules, and talk to a licensed tax professional about your situation.