HSA vs FSA: How to Use Them for Medical Bills
Published July 10, 2026 · 7 min read
An HSA and an FSA both do the same basic magic: they let you pay for medical costs with money that was never taxed. But they are not interchangeable, and choosing or using the wrong one can cost you real money, either in lost tax savings or in a balance that vanishes at year end. Here is how each works, and how to actually put one to work on a bill, the way Steward would.
The one-line version
An HSA is a long-term account you own. An FSA is a short-term benefit your employer runs. That single difference drives almost everything else about how they behave.
How the HSA works
A Health Savings Account is available only if you are enrolled in a qualifying high-deductible health plan. In exchange for that requirement, it is the more powerful account. The money is yours permanently, even if you change jobs. Whatever you do not spend rolls over indefinitely, and many HSAs let you invest the balance so it can grow. Contributions, growth, and withdrawals for qualified medical expenses are all tax-advantaged, which is why some people treat an HSA as a long-term health savings vehicle rather than just a spending account.
How the FSA works
A Flexible Spending Account is set up through your employer, and it does not require a high-deductible plan, so more people can use one. You decide how much to set aside for the year, and the money comes out of your paycheck before taxes. The catch is timing: FSAs are usually use-it-or-lose-it within the plan year. Some employers soften that with a short grace period or a limited carryover, but the balance does not follow you the way an HSA does, and it generally does not carry over freely.
The differences that matter
- Ownership. The HSA is yours and moves with you. The FSA belongs to the employer’s plan.
- Rollover. HSA funds roll over forever. FSA funds are often use-it-or-lose-it.
- Eligibility. The HSA requires a high-deductible plan. The FSA does not.
- Growth. An HSA can often be invested. An FSA is spending money only.
What counts as a qualified expense
Both accounts cover a broad set of qualified medical expenses defined by the IRS. That includes the obvious ones, doctor visits, prescriptions, dental and vision, and many that people overlook, like certain medical supplies and equipment. Because the list is wide, it is worth checking before you pay a medical cost out of a regular checking account, since you may be able to use pre-tax dollars instead.
How to pay a bill with one
- Confirm the expense qualifies. Most medical bills, copays, and prescriptions do.
- Pay directly with the account’s debit card if you have one, or pay out of pocket and reimburse yourself later by submitting the receipt.
- Pay from the bill that matches your Explanation of Benefits, not the first summary, so you are only spending pre-tax dollars on what you actually owe.
- Keep the receipt and the EOB in case you ever need to show the expense qualified.
Where this fits
An HSA or FSA does not lower a bill by itself. It lowers the tax you pay on the money you use to cover it. So the sequence still matters: check the bill for errors, correct anything wrong, apply any discounts or assistance, and then pay what genuinely remains with pre-tax dollars. Getting the bill right comes first, and that is the part Steward handles for you, so the amount you draw from your HSA or FSA is only ever what you truly owe.
This guide is general information, not tax advice. Account rules, eligibility, and contribution limits are set by the IRS and can change each year; confirm the current details for your plan before making decisions.
Frequently asked questions
What is the difference between an HSA and an FSA?
Both let you set aside pre-tax money for medical costs, but they work differently. A Health Savings Account (HSA) is yours to keep, rolls over year to year, can be invested, and requires a high-deductible health plan. A Flexible Spending Account (FSA) is set up through your employer, usually must be used within the plan year, and does not require a high-deductible plan. In short, the HSA is a long-term account you own; the FSA is a use-it-or-lose-it benefit tied to your job.
Can I have both an HSA and an FSA?
Generally not at the same time in a way that overlaps, because a standard FSA makes you ineligible to contribute to an HSA. There is an exception: a limited-purpose FSA, restricted to dental and vision, can be paired with an HSA. If you are choosing during open enrollment, pick based on whether you have a high-deductible plan and how much flexibility you want.
Do I lose my FSA money at the end of the year?
Often, yes, which is the FSA’s biggest catch. Many plans follow use-it-or-lose-it, though your employer may offer a short grace period or let you carry over a limited amount into the next year. Check your specific plan’s rules and spend down the balance on qualified expenses before any deadline. An HSA, by contrast, never expires.
What can I use an HSA or FSA for?
Both cover a wide range of qualified medical expenses defined by the IRS: doctor visits, prescriptions, dental and vision care, many medical supplies, and more. The lists are broad and include items people often forget. When in doubt, check whether an expense is a qualified medical expense before paying out of a regular account.
How do I actually pay a medical bill with one?
Most accounts come with a debit card you can use directly on a bill or copay. If you paid out of pocket, you can usually reimburse yourself later by submitting the receipt. Either way, keep every receipt and Explanation of Benefits, because you may need to show that an expense qualified.
Do I need a high-deductible health plan?
For an HSA, yes. You can only contribute to an HSA if you are enrolled in a qualifying high-deductible health plan. An FSA has no such requirement and can go with most employer plans. This single rule is usually what decides which account is even available to you.