Flexible Spending Accounts are one of the most common employee benefits in the United States, yet surveys consistently show that many workers either skip enrollment or fail to use their full balance. How does an FSA work? At its core, an FSA lets you pay for qualified medical expenses with money deducted from your paycheck before taxes are calculated — saving you between 20% and 40% on healthcare costs depending on your tax bracket. Here is everything you need to know.
The Basic Mechanics of an FSA
An FSA is an employer-sponsored benefit account. During your company’s open enrollment period, you choose an annual contribution amount — up to $3,300 for 2025. That amount is divided evenly across your paychecks for the plan year and deducted before federal income tax, state income tax (in most states), Social Security tax, and Medicare tax are calculated.
The funds go into your FSA, which you can then use to pay for qualified medical expenses throughout the plan year. Most employers issue an FSA debit card for convenient access, though you can also submit claims for reimbursement after paying out of pocket. The plan year typically runs on a calendar-year basis but may follow your employer’s fiscal year.
Full Funding From Day One
One of the most advantageous features of an FSA — and a point that answers how does an FSA work differently from other accounts — is that your entire annual election is available on the first day of the plan year. If you elect $3,000, you can spend the full $3,000 in January even though you have only contributed one month’s worth of payroll deductions.
This is a significant advantage for employees with large planned expenses early in the year. Orthodontic payments, planned surgeries, or new prescription eyeglasses can all be covered immediately. And if you leave your employer before fully contributing, you typically are not required to repay the difference — your employer absorbs that cost.
What You Can Spend FSA Money On
FSA funds cover a wide range of medical, dental, and vision expenses as defined by IRS Publication 502. Common eligible expenses include doctor visit copays and coinsurance, prescription medications, over-the-counter drugs (no prescription needed since the CARES Act of 2020), dental cleanings, fillings, crowns, and braces, eye exams, glasses, and contact lenses, mental health and therapy services, and medical devices like blood pressure monitors and hearing aids.
Menstrual care products — tampons, pads, cups, and liners — are also permanently eligible under the CARES Act. For a detailed list, see our guide on FSA eligible items. And for understanding which everyday products qualify, check our article on HSA/FSA eligible meaning.
The Use-It-or-Lose-It Rule
This is the rule that gives FSAs their reputation for stress. Any funds remaining in your account at the end of the plan year are forfeited — you lose them. The IRS allows employers to offer one (not both) of two safety valves: a grace period of up to 2.5 months after the plan year ends, during which you can still spend leftover funds, or a carryover provision that lets you roll over up to $640 (2024 limit; adjusted annually) into the next plan year.
Your employer decides whether to offer a grace period, a carryover, or neither. Check your plan documents or ask your HR department which option, if any, applies to you. This information is critical for setting your contribution level correctly.
Types of FSAs
There are three main types of FSAs, and understanding the differences matters — especially if you also have or want an HSA.
A Healthcare FSA (or general-purpose FSA) is the most common type. It covers all qualified medical, dental, and vision expenses. However, having a general-purpose FSA disqualifies you from contributing to an HSA, even if you are enrolled in a high-deductible health plan.
A Limited Purpose FSA (LPFSA) covers only dental and vision expenses. This type is designed specifically to work alongside an HSA. If you have an HDHP and an HSA, you can pair them with an LPFSA to get pre-tax savings on dental and vision while maintaining HSA eligibility. Our HSA vs. FSA comparison explores this pairing strategy.
A Dependent Care FSA (DCFSA) is a separate account for dependent care expenses like daycare, preschool, and summer day camp. It has its own contribution limits ($5,000 per household) and different eligibility rules. It is not a healthcare account.
How to Set the Right Contribution Amount
Setting your FSA contribution is the most important decision you will make during enrollment. Contribute too little, and you miss out on tax savings. Contribute too much, and you forfeit the excess. The sweet spot is based on your predictable medical expenses.
Review your past year’s healthcare spending. Add up copays, prescriptions, dental and vision costs, OTC medications, and any planned procedures. If you spent $2,200 last year and expect similar costs, contributing $2,000 to $2,200 gives you a comfortable margin. Factor in any known upcoming expenses like orthodontic work, LASIK, or new glasses.
If this is your first year, start conservatively. A contribution of $1,000 to $1,500 is typically easy to spend on routine healthcare and OTC items without risking significant forfeiture. You can adjust upward in future years as you track your spending patterns.
How FSA Tax Savings Work
The financial benefit of an FSA is straightforward: every dollar you contribute avoids taxation. On a $2,500 contribution, someone in the 22% federal bracket, paying 5% state tax, and 7.65% FICA saves approximately $866 in total taxes. That is $866 more in your pocket for expenses you would have paid anyway.
The savings scale with your tax bracket. Higher earners save a larger percentage per dollar contributed. Even at the 12% federal bracket, the combined savings (including FICA and state tax) typically reach 22% to 25% of the contribution — a meaningful return on money you planned to spend on healthcare regardless. For perspective on whether this savings is worth the forfeiture risk, read our analysis of whether an FSA is worth it.
Frequently Asked Questions
Can I change my FSA election during the year?
Only if you experience a qualifying life event such as marriage, divorce, birth or adoption of a child, death of a dependent, or a change in your or your spouse’s employment. Outside of these events, your election is locked until the next open enrollment period.
Can my spouse use my FSA?
Yes. FSA funds can be used for qualified medical expenses incurred by you, your spouse, and your tax dependents. Many FSA plans issue additional debit cards for spouses. The family members do not need to be covered by your health insurance plan.
What happens to my FSA when I leave my job?
Your FSA access typically ends on your last day of employment. You can submit claims for expenses incurred before that date, usually within a short filing window (often 90 days). COBRA may allow you to continue the FSA, but you would pay the full contribution out of pocket plus administrative fees. Remaining funds you have not claimed are forfeited.
Can I use my FSA at any store?
You can use your FSA debit card at pharmacies, medical providers, and most retailers that sell eligible products. Many stores have systems that automatically approve eligible items and decline ineligible ones at the point of sale. Online retailers like Amazon, CVS, and Walgreens also have FSA-eligible product filters.
Is an FSA the same as an HSA?
No. While both offer pre-tax savings for medical expenses, they differ in key ways. HSAs require a high-deductible health plan, allow funds to roll over indefinitely, and offer investment options. FSAs are tied to your employer, have the use-it-or-lose-it rule, and provide full-year funding upfront. See our detailed comparison.
Make Your FSA Work for You
Understanding how does an FSA work puts you in control of a benefit that can save you hundreds of dollars annually. The key steps are simple: estimate your expenses conservatively, contribute accordingly during open enrollment, use your funds throughout the year for eligible expenses, and track your balance to avoid forfeiture. With a little planning, an FSA becomes one of the most reliable ways to reduce your healthcare costs. Explore our healthcare costs guide for additional strategies, and consult a tax professional if you need help determining the right contribution for your situation.