A flexible spending account, or FSA, lets you set aside a portion of your paycheck before taxes to cover out-of-pocket medical costs, effectively giving you a discount on everything from doctor copays to prescription glasses. The savings come from the fact that FSA contributions dodge federal income tax, Social Security tax, and Medicare tax, which for most people means saving somewhere between 20 and 35 cents on every dollar contributed. The mechanics of using one are straightforward once you know the rules, but a few quirks around timing, eligible expenses, and year-end deadlines trip people up regularly.
How the Tax Advantage Works
When you enroll in a health FSA through your employer, you choose an annual contribution amount. That money gets divided evenly across your paychecks for the year and pulled out before any taxes are calculated. If you earn $50,000 a year and contribute $2,000 to your FSA, your taxable income drops to $48,000. You save on federal income tax at whatever bracket you fall into, plus you skip the 7.65% in Social Security and Medicare taxes on that $2,000. For someone in the 22% federal bracket, that works out to roughly $594 saved on a $2,000 contribution. The money was always yours; it just never got taxed.
Your employer also saves their share of payroll taxes on every dollar you contribute, which is one reason companies are generally happy to offer FSAs. The plan originated with Section 125 of the Internal Revenue Code, passed in 1978, which allowed employers to offer employees a menu of tax-free fringe benefits through what became known as cafeteria plans.1Duke University Press / PubMed Central. Tax policy as social policy: cafeteria plans, 1978-1985 Health FSAs became one of the most popular options in that menu, and they remain so today.
What You Can and Cannot Pay For
The IRS defines eligible expenses broadly under Section 213(d) of the tax code. The list is long, and some items on it surprise people. Here are the categories that cover most of what you will actually spend on:
- Doctor visits: Copays, coinsurance, and deductibles for visits to physicians, specialists, urgent care, and emergency rooms.
- Prescriptions: Any medication requiring a prescription, plus insulin even without one.
- Over-the-counter drugs: Since 2020, OTC medications like pain relievers, allergy pills, and cold medicine are eligible without a prescription.
- Dental care: Cleanings, fillings, crowns, braces, dentures, and most other dental work not considered cosmetic.
- Vision expenses: Eye exams, prescription eyeglasses, contact lenses, contact lens solution, and prescription sunglasses.
- Mental health: Copays for therapy sessions, psychiatrist visits, and some substance abuse treatment costs.
- Medical equipment: Crutches, blood pressure monitors, diabetic supplies, and similar devices.
- Menstrual products: Tampons, pads, and similar items became eligible in 2020.
The list of ineligible expenses catches people off guard just as often. Cosmetic procedures like teeth whitening, elective plastic surgery, and non-prescription supplements are generally not covered. Gym memberships remain ineligible despite occasional rumors to the contrary, unless a doctor prescribes exercise for a specific medical condition and your plan administrator agrees to cover it, which is rare. Health insurance premiums themselves cannot be paid with FSA dollars either.
When in doubt, the FSA Store (an online retailer specializing in FSA-eligible products) and your plan administrator’s website usually maintain searchable lists of approved items. Keeping receipts matters: if your plan administrator audits a purchase and you cannot prove it was eligible, you may have to pay the money back with taxes and penalties.
Choosing the Right Contribution Amount
The IRS sets an annual cap on health FSA contributions, which adjusts slightly for inflation each year. For 2025, the limit is $3,300. You do not have to contribute the maximum. In fact, the single most important decision in the whole process is estimating your annual medical spending accurately, because money left in the account at the end of the plan year is generally forfeited.
Start by reviewing what you spent out of pocket over the past year or two. Pull up insurance claims, pharmacy receipts, and any dental or vision bills. Add in predictable costs for the coming year: if you know you need new glasses, are planning a dental procedure, or take a regular prescription, count those. Then pad the number slightly for unexpected copays and OTC purchases, but not so much that you are gambling on expenses that may never materialize.
Research on FSA participation suggests that people who have predictable, recurring medical expenses tend to set their contribution amounts more accurately, while those with uncertain costs are more likely to over- or under-contribute.2ScienceDirect. An examination of flexible spending accounts If your health spending is genuinely unpredictable, starting with a conservative amount is smarter than going big and risking forfeiture.
How to Actually Pay With Your FSA
Most FSA plans today issue a debit card linked to your account. You swipe it at the pharmacy, the doctor’s office, or an online retailer, and the purchase is deducted from your FSA balance automatically. Many merchants with IRS-approved inventory systems will process only eligible items through the card, which simplifies things. At a drugstore, for instance, the card may cover your allergy medication but decline if you try to buy a non-eligible item with it.
If you pay out of pocket first, you can submit a claim for reimbursement through your plan administrator. This usually means uploading a receipt or explanation of benefits (EOB) from your insurer to a web portal or mobile app. Reimbursement typically takes a few business days to a couple of weeks depending on the administrator. Keep in mind that most plans require you to submit reimbursement claims within a set window after the plan year ends, often 90 days, so do not sit on receipts indefinitely.
One feature that works in your favor: unlike a health savings account, your full annual FSA election is available on the first day of the plan year, even though the payroll deductions happen gradually throughout the year. If you elected $2,400 and your plan year starts January 1, you can spend all $2,400 in January even though only $200 has been deducted from your paycheck so far. This is sometimes called the “uniform coverage rule,” and it is built into the way health FSAs work by regulation. If you leave your job mid-year after spending more than you have contributed, you generally do not have to pay the difference back.
The Use-It-or-Lose-It Rule
This is the feature that makes people nervous about FSAs, and reasonably so. Any money remaining in your health FSA at the end of the plan year is forfeited to your employer. You cannot roll it into next year’s account, withdraw it as cash, or transfer it to an HSA. The rule exists because the IRS treats FSA contributions as a tax benefit with a defined spending period, not as a savings vehicle.
There are two partial exceptions, though your employer gets to decide which one to offer, if any:
- Grace period: Your plan may extend the deadline by up to two and a half months after the plan year ends. If your plan year runs on the calendar year, that means you have until March 15 to spend remaining funds on eligible expenses incurred during the grace period.
- Carryover: Your plan may allow you to roll over a limited amount of unused funds into the next plan year. For 2025, the IRS carryover limit is $660. Any amount above the carryover threshold is still forfeited.
Your employer can offer one of these options or neither, but not both. Check your plan documents or ask HR which applies to you. If your plan offers neither, every dollar you do not spend by December 31 (or whenever your plan year ends) is gone.
This deadline pressure is the single biggest source of FSA frustration. Research shows that FSA participants tend to spend their elected amounts relatively early in the year, which suggests people are aware of the forfeiture risk and act accordingly.2ScienceDirect. An examination of flexible spending accounts If you find yourself approaching year-end with a surplus, stock up on eligible items you will use anyway: contact lenses, prescription refills, first-aid kits, sunscreen (yes, it is eligible), and OTC medications.
FSA Versus HSA
People often confuse FSAs and health savings accounts (HSAs) because both let you pay for medical expenses with pre-tax money. The differences matter a lot for deciding which one to use, or whether you can use both at all.
An HSA is available only to people enrolled in a high-deductible health plan (HDHP). An FSA is available through most employer-sponsored health plans regardless of deductible level. That is the first and most basic gate: if your health insurance is not an HDHP, you are not eligible for an HSA, so an FSA is your tax-advantaged option.
The biggest practical difference is what happens to unused money. HSA funds roll over indefinitely, year after year, and the account stays with you even if you change jobs. FSA funds are subject to the use-it-or-lose-it rule described above. This makes HSAs function more like a long-term savings or even retirement vehicle, while FSAs are strictly a spend-this-year tool.
HSAs also offer a triple tax advantage: contributions are pre-tax, growth is tax-free, and withdrawals for eligible medical expenses are tax-free. FSAs share the first and third benefits but do not have an investment component because the money is not meant to accumulate.
If you have an HDHP with an HSA, you generally cannot also have a standard health FSA. You can, however, pair an HSA with a limited-purpose FSA, which restricts eligible expenses to dental and vision costs only. This combination lets you reserve your HSA balance for larger or future medical costs while using the limited-purpose FSA for routine eye and dental care.
Common Mistakes and How to Avoid Them
The most frequent FSA mistakes are not exotic. They are predictable, and all of them are avoidable with a little planning.
Over-contributing is the classic error. People set their election too high, cannot spend it all, and forfeit the remainder. A conservative first-year contribution that you can always increase the following year is a safer approach than guessing optimistically. Remember, you can adjust your election during your employer’s open enrollment period each year, and also after a qualifying life event like a marriage, birth of a child, or change in employment status.
Forgetting to submit reimbursements is another common pitfall. If you paid out of pocket for an eligible expense and did not use the FSA debit card, the money does not come back to you automatically. You have to file the claim. Set a recurring reminder to check for unreimbursed expenses every month or two.
Using the FSA card for ineligible items creates a different headache. If an ineligible purchase goes through on your FSA debit card, your plan administrator will flag it and ask you to either provide documentation that it was eligible or repay the amount. Ignoring these requests can result in the card being suspended or the amount treated as taxable income.
Missing the claims deadline stings worst of all. After your plan year ends (plus any grace period), unclaimed reimbursements are gone. This is distinct from the forfeiture rule: even if you spent the money on an eligible expense during the plan year, you can still lose the reimbursement if you file the claim too late.
Who Benefits Most From an FSA
FSAs deliver the most value to people who have predictable, recurring healthcare expenses and earn enough that the tax savings are meaningful. If you wear glasses, take a daily medication, see a therapist regularly, or have kids who need routine dental work, you can estimate your annual costs with reasonable accuracy and contribute confidently.
Research has consistently found that FSA participation rises with income.2ScienceDirect. An examination of flexible spending accounts This makes sense mechanically: higher earners are in higher tax brackets and therefore save a larger percentage on each dollar contributed. A person in the 32% bracket saves more per FSA dollar than someone in the 12% bracket, even though both skip the same payroll taxes. Additionally, lower-income workers may feel less comfortable locking up money they might need for non-medical expenses, especially given the forfeiture risk.
People living in states with no income tax also participate less frequently, which is logical since part of the FSA’s value comes from avoiding state income tax on contributions.2ScienceDirect. An examination of flexible spending accounts If you live in Texas, Florida, or another state without an income tax, the savings are still real from federal and payroll taxes, but the total percentage saved on each dollar is a bit lower than it would be for someone in, say, California or New York.
That said, even modest earners can benefit if their out-of-pocket costs are predictable. Someone in the 12% federal bracket who contributes $1,000 still saves close to $200 in combined taxes. The question is not whether the tax benefit exists, but whether the forfeiture risk makes it a bad bet for your particular spending pattern.
Dependent Care FSAs Are a Separate Animal
Employers sometimes offer a dependent care FSA alongside the health FSA, and the two share a name and a basic structure but differ in almost every practical detail. A dependent care FSA covers childcare expenses for children under 13, or care for a disabled spouse or dependent, so that you (and your spouse, if applicable) can work. Think daycare, preschool, before- and after-school programs, and summer day camp.
The contribution limit for dependent care FSAs is $5,000 per household for married couples filing jointly, or $2,500 if married and filing separately. Unlike the health FSA, this limit has not changed in decades and is not indexed for inflation, which means it buys considerably less childcare than it did when the benefit was introduced. The dependent care FSA also does not front-load your balance: you can only be reimbursed up to the amount that has actually been deducted from your paychecks so far, which means large early-year expenses might only be partially reimbursable until enough contributions accumulate.
If your employer offers a dependent care FSA and you have childcare costs, it is worth comparing the FSA tax savings against the Child and Dependent Care Tax Credit, which covers similar expenses. In some income ranges, the credit is more valuable; in others, the FSA wins. You can use both, but not for the same dollars of expense, so the math requires a little care. A tax professional or a good online calculator can tell you which combination saves more in your specific situation.
What Happens to Your FSA If You Leave Your Job
Health FSAs are tied to your employer. If you quit, get laid off, or retire, you generally lose access to the account on your last day of employment (or at the end of the month, depending on your plan). Any balance remaining in the account is forfeited. You can submit reimbursement claims for eligible expenses incurred before your termination date, but not for anything that happens after.
There is one narrow exception: COBRA continuation coverage. Under COBRA, you may be eligible to continue your FSA for the remainder of the plan year by paying the full contribution amount yourself, including the portion your employer previously subsidized through payroll. In practice, few people do this because paying after-tax dollars into an FSA (while also covering COBRA premiums for your health insurance) rarely pencils out unless you have a large remaining balance and a known upcoming expense. Still, if you have $2,000 sitting in your FSA on the day you leave and a scheduled surgery the following month, COBRA continuation might be worth a close look.
The fact that FSAs are not portable is one of their biggest structural downsides compared to HSAs. If you think a job change is on the horizon, consider front-loading your FSA spending early in the year. Since your full election is available from day one, you can use the funds before you leave and only have a portion deducted from your final paychecks. If you leave with more spent than contributed, your employer absorbs the difference.