A Clear Explanation of Your Flexible Spending Account
Nearly 30 million Americans have access to a Flexible Spending Account through their employer, yet many of them leave money on the table because they do not fully understand the mechanics. If you have been asking “how does FSA work,” you are not alone — and the concept is simpler than most benefits documents make it seem. An FSA lets you set aside pre-tax dollars from your paycheck to pay for qualified medical expenses, effectively giving you a discount on healthcare equal to your marginal tax rate.
For someone in the 24 percent federal tax bracket who also pays state income tax and FICA taxes, an FSA can reduce the real cost of medical expenses by 30 percent or more. That is a significant savings on everything from doctor copays and prescriptions to contact lenses and over-the-counter pain relievers. Below, we walk through exactly how the account operates from enrollment to year-end.
How FSA Contributions Work
You elect a contribution amount during your employer’s open enrollment period, typically held in the fall for the upcoming plan year. For 2025, the IRS caps health FSA contributions at $3,300 per employee. Your employer may set a lower limit, but it cannot exceed the IRS maximum.
Once you set your election, your employer divides the total amount into equal payroll deductions spread across the plan year. If you elect $3,300 and are paid biweekly, approximately $126.92 comes out of each paycheck before federal income tax, state income tax (in most states), and FICA taxes are calculated. That pre-tax treatment is the core benefit of the FSA.
You generally cannot change your election mid-year unless you experience a qualifying life event — marriage, divorce, birth of a child, loss of other coverage, or a change in employment status. Some employers also allow changes if the cost of a qualified plan changes significantly.
Full Balance Available on Day One
One of the most distinctive features of a healthcare FSA is the uniform coverage rule. Your full annual election is available on the first day of the plan year, even though you have not yet contributed the entire amount through payroll deductions. If you elect $3,300 and incur a $3,300 dental bill in January, you can submit the claim and be reimbursed in full — even though only one or two paychecks have been deducted so far.
This is a meaningful advantage over an HSA, where you can only spend what you have actually deposited. The front-loaded access makes the FSA especially useful for planned procedures early in the year.
What Can You Spend FSA Funds On?
FSA-eligible expenses are defined by IRS Section 213(d) and IRS Publication 502. The CARES Act of 2020 expanded the list to include all over-the-counter medications without a prescription and menstrual care products. Today, eligible expenses include doctor and specialist visits, hospital and emergency room charges, prescription medications, over-the-counter drugs (pain relievers, allergy meds, cold remedies), dental care (exams, fillings, orthodontics), vision care (glasses, contacts, LASIK), mental health services, physical therapy, medical equipment, sunscreen (SPF 15+), and first-aid supplies.
Items that do not qualify include cosmetic procedures, gym memberships, general vitamins and supplements (unless medically necessary), and most insurance premiums. For the full rundown, see our FSA eligible items list.
How to Use Your FSA Funds
Most FSA plans offer two ways to access your funds.
FSA Debit Card
Many plans issue a debit card linked to your FSA. You can swipe it at pharmacies, doctor’s offices, and online retailers that sell eligible products. The card’s system often auto-verifies eligibility at the point of sale. If a purchase is flagged, you may be asked to provide a receipt or explanation later.
Manual Reimbursement
If you pay out of pocket, you submit a claim to your FSA administrator with a receipt or Explanation of Benefits showing the expense amount, the date, and the provider. Reimbursement is typically processed within a few business days and deposited into your bank account.
Keep all receipts and documentation. Your administrator or the IRS can request substantiation for any FSA transaction.
The Use-It-or-Lose-It Rule
This is the rule that catches people off guard. Unlike an HSA, FSA funds generally must be spent within the plan year. If you do not use your balance by the deadline, you forfeit the remainder. Your employer may offer one of two relief options — but not both:
Grace period: An additional period of up to 2.5 months after the plan year ends during which you can incur expenses against the previous year’s balance. Rollover: Up to $660 (for 2025) can carry over into the next plan year. Any amount above the rollover limit is forfeited.
Not every employer offers either option. Check your plan documents to understand which — if any — applies to you. The use-it-or-lose-it feature is the primary reason financial advisors recommend conservative FSA elections: contribute only what you are confident you will spend.
FSA vs. HSA: Key Differences
Understanding how does FSA work often leads to a comparison with the Health Savings Account. The two accounts share the benefit of pre-tax contributions and tax-free spending on medical expenses, but they differ in important ways.
An FSA is available with any employer-sponsored health plan, while an HSA requires enrollment in a high-deductible health plan. FSA funds expire at year-end (subject to grace period or rollover provisions), while HSA funds roll over indefinitely. The FSA contribution limit for 2025 is $3,300, compared to $4,300 (individual) or $8,550 (family) for HSAs. FSA accounts are owned by the employer, while HSAs are owned by the individual and are portable.
Some people have access to both accounts simultaneously through a Limited Purpose FSA. For more details, see our guides on HSA and FSA comparisons and Limited Purpose FSAs.
Tips for Maximizing Your FSA
Estimate your annual medical spending before open enrollment. Review last year’s out-of-pocket costs — copays, prescriptions, dental work, glasses — and use that as your baseline. Factor in any planned procedures such as orthodontics, LASIK, or a new pair of glasses.
If you reach the end of the plan year with funds remaining, schedule dental cleanings, stock up on eligible OTC products, order a new pair of prescription glasses, or purchase qualifying medical supplies. Our healthcare costs guide offers additional strategies for reducing your medical spending throughout the year.
Frequently Asked Questions
Can both spouses have an FSA?
Yes. If both spouses have employer-sponsored plans that offer FSAs, each can contribute up to the IRS limit. However, each spouse can only be reimbursed for expenses covered by their own FSA, and you cannot submit the same expense to both accounts.
What happens to my FSA if I leave my job?
In most cases, your FSA ends when your employment ends. You can only be reimbursed for expenses incurred before your termination date. Some employers offer COBRA continuation for FSAs, but this is uncommon and often not cost-effective since you would pay the full contribution amount plus a 2 percent administrative fee without the pre-tax benefit.
Can I use my FSA for my dependents?
Yes. Your FSA can cover qualified medical expenses for your spouse and any tax dependents claimed on your return, including children under age 26 for certain expenses. Keep separate documentation for each family member.
Is there a minimum FSA contribution?
The IRS does not set a minimum, but your employer may. Many plans allow elections as low as $100 or $250 per year. Contributing even a small amount can save you money on predictable expenses like copays and prescriptions.
Put Your FSA to Work
Now that you understand how an FSA works, the next step is making a smart contribution election at your next open enrollment. Start by reviewing your expected medical expenses, choose a contribution level you are confident you will use, and keep your receipts organized throughout the year. The pre-tax savings add up quickly, especially when combined with strategic year-end spending. For a foundational overview, explore our article on what an FSA is, and visit our healthcare policy guide for the broader regulatory landscape.