What Is S125med? FSA Limits, Rollover, and Mid-Year Changes

If you see “S125,” “Section 125,” or something like “S125med” listed on your paycheck, it is a Section 125 pre-tax deduction on your paycheck for health benefits. The line represents money your employer pulled from your gross pay before calculating federal income tax and FICA, which is why the taxable wages in Box 1 of your W-2 end up lower than your actual salary. The arrangement gets its name from Section 125 of the Internal Revenue Code, which authorizes employers to offer a “cafeteria” of benefits employees can pay for with untaxed dollars instead of taxable cash.¹

What the Deduction Actually Pays For

Two things usually sit behind an S125 line. The first is your share of employer-sponsored health, dental, or vision insurance premiums, routed through what’s called a Premium Only Plan, or POP. If your employer covers part of the premium and bills you for the rest, the POP takes your portion out before taxes are figured.

The second is a Health Flexible Spending Account. You pick a dollar amount at open enrollment, and the plan splits it into equal deductions across every paycheck of the year. The money is set aside to reimburse out-of-pocket medical costs that insurance doesn’t fully cover, like copays, deductibles, dental work, and prescriptions.

Both run through the same pre-tax mechanism, which is why they often appear under the same payroll code. If your pay stub itemizes benefits separately, you may see one line for the health premium and another for the FSA; if it rolls them together, “S125” is the umbrella label.

How Much the Pre-Tax Treatment Saves You

Salary reduction contributions to a cafeteria plan are generally exempt from federal income tax, FICA (Social Security and Medicare), and federal unemployment tax.² For someone earning $60,000 who routes $3,000 through the plan, the combined savings often reach $900 or more, depending on marginal tax bracket. The employer saves too, since they don’t owe the matching payroll tax on money that bypasses wages.

Most states follow the federal treatment and exempt S125 contributions from state income tax as well, but a few don’t fully conform. If you want to confirm what’s happening in your state, compare the state wages box on your W-2 to the federal wages box: if they match, the state is taxing the S125 money; if the state wages are higher, the state is adding it back.

Health FSA Limits and What You Can Spend It On

The IRS caps Health FSA salary reductions each year. For plan years beginning in 2026, the maximum is $3,400 per employee.³ A working spouse at a different employer can elect their own $3,400 in a separate account.

The full elected amount is available on day one of the plan year, before the payroll deductions have caught up. Elect $3,400 and need $2,000 of dental work in January? You can use the full balance immediately, and the employer absorbs the risk if you leave before contributing the rest.⁴

Eligible expenses are the ones that count as “medical care” under the tax code, meaning diagnosis, treatment, and prevention of disease.⁵ In practice:

Doctor and specialist copays
Prescription medications
Dental work, including fillings, crowns, and orthodontics
Vision expenses like eyeglasses, contact lenses, and eye exams
Over-the-counter medications such as pain relievers, allergy medicine, and cold remedies, with no prescription needed since the CARES Act change in 2020
Menstrual care products including tampons, pads, and cups

The CARES Act permanently added OTC medications and menstrual products to the eligible list.⁶ Health insurance premiums are not FSA-eligible, since those are handled by the POP side of the plan. Cosmetic procedures and daily vitamins don’t qualify either.

Use-It-or-Lose-It, and the Two Safety Valves

Money left in a Health FSA at the end of the plan year is generally forfeited back to the employer.⁷ Overshooting means losing cash; undershooting means missing tax savings. A realistic election usually comes from looking at last year’s out-of-pocket spending and layering in anything planned, like new glasses or a procedure you’ve been putting off.

Employers can soften the deadline with one of two features, but not both:⁷

Carryover: a limited amount of unused funds rolls into the next plan year. For 2026, the maximum carryover is $680. Anything above that is still forfeited, and the carryover does not reduce next year’s $3,400 election.³
Grace period: up to an extra two and a half months after the plan year ends to incur new eligible expenses against last year’s balance. For a calendar-year plan, that runs through March 15.⁴

Which one your plan uses, if either, is spelled out in the Summary Plan Description from your HR or benefits portal. Separate from either is the run-out period, which is the extra time (often around 90 days) to submit claims for expenses you already incurred before the plan year closed. Missing the run-out deadline means losing reimbursement for charges you had every right to claim.

Why You Can’t Change the Deduction Mid-Year

Once you lock in a Section 125 election, it holds for the full plan year. The irrevocability rule is there to stop employees from only funding the account when a big bill is on the horizon.⁸

A qualifying change in status is the exception, and the Treasury regulations list which events count, provided the change you request is consistent with the event:⁸

Marital status: marriage, divorce, legal separation, annulment, or death of a spouse
Number of dependents: birth, adoption, or placement for adoption
Employment status: you, your spouse, or a dependent starts or stops working, switches between full-time and part-time, or takes unpaid leave
Dependent eligibility: a child ages out of coverage or loses student status
Residence: a move that changes your provider network access

The requested change has to line up with the event. A new baby justifies adding the child and raising your FSA election; it does not justify dropping dental coverage. Most plans give you a short window to act, commonly 30 to 60 days, set by the plan document rather than federal regulation. Miss it, and you’re locked in until the next open enrollment.

What Happens to the Deduction When You Leave

Termination stops future S125 deductions immediately. For the Health FSA, two different outcomes are possible depending on where you stand.

If you’ve already spent more than you’ve contributed, you keep the reimbursements. The uniform coverage rule that makes the full election available on day one also prevents the employer from clawing back the difference.⁴

If you’ve contributed more than you’ve spent, the unspent balance is forfeited unless you elect COBRA continuation for the FSA. Employers with 20 or more employees generally have to offer it.⁹ COBRA for an FSA is rarely worth it: you pay the full remaining annual election (prorated monthly) plus a 2% administrative fee, in after-tax dollars. It only makes sense when the balance you’d recover clearly exceeds what you’d pay in premiums for the rest of the plan year.

Who Can’t Have an S125 Deduction at All

The tax code limits cafeteria plan participation to “employees.”¹ That excludes:

Sole proprietors and other self-employed individuals
Partners in a general or limited partnership
S corporation shareholders who own more than 2% of the company’s stock

These owners are treated as self-employed under the tax code even when they draw a regular salary. A 3% S corporation shareholder working full-time cannot route health premiums through the company’s Section 125 plan, despite showing up on payroll. The alternatives are a Health Savings Account (if paired with a qualifying high-deductible health plan) or the self-employed health insurance deduction on the personal return. If you fall in this group and see an S125 line anyway, flag it with your payroll department: the pre-tax treatment is not valid for you, and leaving it in place creates a reporting problem at year end.

1
Office of the Law Revision Counsel. 26 USC 125 Cafeteria Plans
2
Internal Revenue Service. FAQs for Government Entities Regarding Cafeteria Plans
3
Internal Revenue Service. Revenue Procedure 2025-32
4
Internal Revenue Service. Modification of Use-or-Lose Rule for Health Flexible Spending Arrangements and Clarification Regarding 2013-2014 Non-Calendar Year Salary Reduction Elections Under Section 125 Cafeteria Plans Notice 2013-71
5
Office of the Law Revision Counsel. 26 USC 213 Medical, Dental, Etc., Expenses
6
Internal Revenue Service. IRS Outlines Changes to Health Care Spending Available Under CARES Act
7
Internal Revenue Service. Publication 969 (2025), Health Savings Accounts and Other Tax-Favored Health Plans
8
GovInfo. Treasury Regulation 1.125-4 Permitted Election Changes
9
U.S. Department of Labor. Continuation of Health Coverage (COBRA)