A Flexible Spending Account is funded by a pre-tax payroll deduction: you pick an annual contribution during open enrollment, and your employer splits that amount evenly across your pay periods and withholds it from your gross wages before federal income tax, Social Security and Medicare tax, and most state income taxes are calculated. Because the money never counts as taxable compensation, the savings show up automatically in every paycheck rather than at tax time.
How the Pre-Tax Deduction Works
FSAs run through what the tax code calls a cafeteria plan, authorized by Section 125 of the Internal Revenue Code.1Office of the Law Revision Counsel. 26 USC 125 – Cafeteria Plans You agree to reduce your salary by a set amount, and that reduction moves straight into the FSA. Your employer’s payroll system treats only the remaining pay as your taxable wages.
The deduction skips three layers of tax at the same time: federal income tax, FICA (6.2% Social Security plus 1.45% Medicare, or 7.65% combined), and, in most states, state income tax.2Internal Revenue Service. Topic No. 751, Social Security and Medicare Withholding Rates That triple exemption is what makes an FSA more powerful than paying medical or dependent care costs with after-tax money and trying to deduct them later. In fact, medical expenses claimed on Schedule A only count above 7.5% of adjusted gross income, while every FSA dollar is untaxed regardless of your total spending.3Internal Revenue Service. Publication 502 (2025), Medical and Dental Expenses
On your W-2, FSA contributions simply never appear as taxable wages in Box 1.4Internal Revenue Service. Publication 969 (2025), Health Savings Accounts and Other Tax-Favored Health Plans Dependent Care FSA benefits do show up separately in Box 10, but Health Care FSA contributions may only appear informationally in Box 14, if at all.
What the Numbers Look Like on a Paycheck
Say you earn $5,000 a month and elect $200 a month into a Health Care FSA. Your taxable income drops to $4,800. In a 22% federal bracket with a 5% state rate, adding the 7.65% FICA hit gives a combined tax rate of roughly 34.65% on that $200, so you save about $69.30 each month. You put $200 into the account, but your take-home only drops by about $130.70.
Your employer benefits too. They avoid the employer-side 7.65% FICA match on every dollar you route through the FSA, which is a large reason most employers are willing to sponsor these plans.2Internal Revenue Service. Topic No. 751, Social Security and Medicare Withholding Rates
The Social Security Tradeoff
Because FSA contributions also reduce your Social Security taxable wages, they can slightly lower your future Social Security retirement benefit. For most contributors the reduction is small compared to the immediate tax savings, but if you contribute the maximum over many years, it’s worth being aware of.
How Much Can Be Deducted in 2026
You choose the total annual amount during your employer’s open enrollment, and the IRS caps how high that election can go.
Health Care FSA
For plan years beginning in 2026, the salary-reduction limit for a Health Care FSA is $3,400, up from $3,300 in 2025.5Internal Revenue Service. General Instructions for Forms W-2 and W-3 (2026) Any employer matching or seed money generally does not count toward the $3,400 cap, unless you had the option to take it as cash instead.
Dependent Care FSA
The Dependent Care FSA household limit rose sharply for 2026, from $5,000 to $7,500, or from $2,500 to $3,750 if you’re married filing separately.6Office of the Law Revision Counsel. 26 USC 129 – Dependent Care Assistance Programs It covers care for children under 13 or dependents who can’t care for themselves.7Internal Revenue Service. Publication 503 (2025), Child and Dependent Care Expenses One trap catches people: your exclusion can’t exceed the lower of your earned income or your spouse’s earned income, so if one spouse doesn’t work, the DCFSA benefit may be limited or unavailable. Highly compensated employees may also see a lower cap if the plan needs to pass nondiscrimination testing.
Locking In and Splitting Up the Election
Your election is generally locked for the entire plan year. You can only change it mid-year after a qualifying life event such as marriage, a birth, or a change in your or your spouse’s employment.8U.S. Office of Personnel Management. Life Events The election must be in place before the plan year starts, meaning you commit before the wages are earned.
Payroll then divides your annual number evenly across your pay periods. Elect $2,600 with a biweekly employer, and exactly $100 comes out of each of your 26 checks. The deduction runs automatically until the plan year ends.
What You Can Actually Spend Before the Deductions Add Up
Even though the deduction is spread across the year, your access to the money depends on which FSA you have.
Health Care FSA
A Health Care FSA follows the uniform coverage rule: your full annual election is available on day one of the plan year, no matter how little has been deducted so far.9Internal Revenue Service. Notice 2013-71 If you elected $3,400, you can submit a $3,400 claim in January after one payroll deduction. That makes the account useful for planned early-year expenses like scheduled surgery or orthodontia.
Dependent Care FSA
The DCFSA is pay-as-you-go. You can only be reimbursed up to what has already been withheld from your paychecks.10FSAFEDS. Dependent Care FSA Three biweekly deductions of $288 gives you $864 to draw against, even if your annual election is $7,500. Budget upfront costs like summer camp deposits and daycare enrollment fees around that timing.
What Happens to Deductions You Don’t Spend
Any balance left in your account at the end of the plan year is forfeited to your employer. This is the use-it-or-lose-it rule, and it’s why most people are conservative with their election. Employers can offer one of two softening options, but not both.11Internal Revenue Service. IRS: Eligible Employees Can Use Tax-Free Dollars for Medical Expenses
- A grace period of up to two and a half months after the plan year ends to incur new eligible expenses. For a calendar-year plan, that’s through March 15.4Internal Revenue Service. Publication 969 (2025), Health Savings Accounts and Other Tax-Favored Health Plans
- A carryover of up to $680 of unused Health Care FSA funds from 2026 into the following plan year. Employers can cap this lower but not higher, and anything above the carryover amount is still forfeited.
Separately, most plans include a run-out period, often 90 days after year-end, giving you time to submit claims for expenses you already incurred during the plan year. A run-out period is a paperwork deadline; a grace period lets you spend on new expenses. Missing the run-out deadline means losing reimbursement for money you already paid out of pocket.
If You Leave the Job Mid-Year
The uniform coverage rule cuts both ways for a Health Care FSA. If you elected $3,400, spent $2,800 by June, but had only $1,400 withheld from your paychecks, your employer absorbs the $1,400 gap and cannot ask you to repay it. Flip it around, and if you’ve contributed more than you’ve spent, the unspent balance is typically forfeited. Your claims window usually closes on your last day or the end of that month, depending on the plan.
Employers must offer COBRA continuation for the Health Care FSA, but it rarely pencils out.12U.S. Department of Labor. COBRA Continuation Coverage You’d pay the full contribution plus a 2% administrative fee with after-tax dollars, which erases the entire tax advantage. It only makes sense if you’ve contributed little so far but have large, predictable expenses still coming.
The Dependent Care FSA is simpler at termination. Because it’s pay-as-you-go, you can still submit claims for eligible expenses incurred before your last day, up to the balance already deducted from your checks.