Common Section 125 Mistakes and How to Avoid Them
Section 125 plans are one of the best tax-saving tools available to employers. But they come with rules — and when those rules are broken, the consequences range from annoying to expensive. Back taxes, penalties, plan disqualification, and angry employees are all on the table.
The frustrating part? Most Section 125 mistakes are entirely avoidable. They happen because someone didn’t know the rule existed, the plan was set up hastily, or ongoing administration fell through the cracks. For guidance on staying compliant throughout the year, see Section 125 Compliance 2026.
Here are the 10 most common mistakes we see, what happens when you make them, and how to fix or prevent each one.
Mistake #1: No Written Plan Document
What happens: The IRS requires a written plan document for every Section 125 plan. Without one, your cafeteria plan doesn’t legally exist — even if you’ve been running pre-tax deductions for years.
The consequence: All pre-tax deductions may be reclassified as taxable income. The employer owes back FICA taxes plus interest and penalties. Affected employees owe back income taxes. The IRS can go back multiple years.
How to avoid it: Have a compliant plan document prepared by a qualified TPA or benefits attorney. The document must be signed before the plan year begins. If you don’t have one now, get one immediately — it won’t fix the past, but it protects you going forward.
How common is this? More common than you’d think. Surveys suggest that 20–30% of small employers running pre-tax deductions don’t have a formal plan document.
Mistake #2: Skipping Nondiscrimination Testing
What happens: Section 125 plans require three annual nondiscrimination tests: the eligibility test, the benefits and contributions test, and the key employee concentration test. Many employers either don’t know about this requirement or assume it’s optional.
The consequence: If the plan fails testing, the tax benefits for highly compensated employees (HCEs) and key employees are reduced or eliminated. Those employees’ pre-tax deductions may be reclassified as taxable. If you never test, you won’t know you’re out of compliance until an audit — and by then, multiple years may be affected.
How to avoid it: Include nondiscrimination testing in your TPA’s annual service. Test at least once per year, ideally both mid-year (preliminary) and year-end (final). If you have fewer than 100 employees, consider a Simple Cafeteria Plan, which provides a safe harbor from testing requirements.
Who is an HCE? For 2026, a highly compensated employee is anyone who earned more than $160,000 in the prior year or is a more-than-5% owner.
Mistake #3: Wrong Effective Date or Retroactive Adoption
What happens: The plan document is signed after the plan year has already started. Someone decides in March to “set up a Section 125 plan effective January 1.”
The consequence: Retroactive adoption is not permitted under Section 125. Pre-tax deductions taken before the plan was formally adopted are invalid. The employer may owe back FICA taxes on those deductions.
How to avoid it: Plan ahead. If you’re starting a new plan, allow 4–6 weeks for setup. If you’re renewing, have amendments signed before the new plan year. If you missed the deadline, start the plan on the first day of the next available period — don’t backdate it.
Mistake #4: Allowing Improper Mid-Year Election Changes
What happens: An employee asks to change their FSA election mid-year because they realize they elected too much (or too little). The HR team processes the change to be helpful.
The consequence: Section 125 elections are irrevocable for the plan year unless the employee experiences a qualifying life event. Allowing changes outside of qualifying events violates the plan terms and can jeopardize the plan’s tax-qualified status.
Qualifying life events include:
- Marriage or divorce
- Birth or adoption of a child
- Death of a spouse or dependent
- Change in employment status (employee or spouse)
- Loss or gain of other coverage
- Significant change in cost of coverage (employer-initiated)
- COBRA qualifying event
- Judgment, decree, or order (QDRO)
How to avoid it: Train your HR team on what constitutes a qualifying life event. Have a clear process: the employee submits documentation of the event, HR verifies it qualifies, and the change is processed within the plan’s specified timeframe (typically 30 days from the event). Don’t make exceptions — even well-intentioned ones.
Mistake #5: Not Offering the Plan to All Eligible Employees
What happens: The plan is offered to salaried employees but not hourly workers. Or it’s available at headquarters but not at the satellite office. Or new hires are told about it informally rather than through a systematic enrollment process.
The consequence: Excluding eligible employees violates nondiscrimination rules and can cause the plan to fail testing. It can also create legal liability if excluded employees discover they were denied a benefit they should have received.
How to avoid it: Define eligibility clearly in the plan document and apply it consistently. Every employee who meets the eligibility criteria must be offered the opportunity to participate — even if you expect they’ll decline. Document your enrollment process and keep records of who was offered the plan and when.
Mistake #6: Failing to Track Qualifying Life Events
What happens: An employee gets married, has a baby, or loses spousal coverage, but nobody processes a mid-year election change because the event wasn’t reported or tracked.
The consequence: The employee misses the window to adjust their benefits, leading to frustration and potential coverage gaps. In some cases, the employer may face liability for failing to process a change the employee requested.
How to avoid it: Create a clear process for employees to report qualifying life events. Include life event procedures in your enrollment materials and employee handbook. Set up reminders to HR when employees report events like marriage, birth, or address changes. Most benefits platforms have built-in life event workflows — use them.
Mistake #7: Ignoring COBRA for FSA Participants
What happens: An employee with an FSA balance terminates employment. The employer doesn’t offer COBRA continuation for the FSA because they didn’t realize it was required.
The consequence: Health FSAs with employer contributions are subject to COBRA. Failing to offer COBRA continuation for the FSA can result in penalties — up to $110 per day per affected individual under ERISA, plus potential excise taxes under the IRC.
The nuance: If the FSA is funded solely through employee salary reductions, COBRA is technically required but rarely makes economic sense for the departing employee (since they’d have to pay the full remaining annual contribution with after-tax dollars). However, you still must offer it.
How to avoid it: Include FSA COBRA in your COBRA administration process. If you use a COBRA administrator, make sure they know about your FSA plan. Track which terminating employees have active FSA balances.
Mistake #8: Exceeding Contribution Limits
What happens: An employee elects more than the annual maximum for a Health FSA ($3,300 in 2026) or Dependent Care FSA ($5,000 for most filers). Or mid-year enrollment changes push total contributions over the limit.
The consequence: Contributions above the limit lose their tax-advantaged status. Excess amounts are includable in the employee’s taxable income. If not caught and corrected, it creates a reporting problem on the employee’s W-2.
How to avoid it: Configure your enrollment system with hard limits that prevent over-election. When processing mid-year changes, prorate the remaining limit based on the remaining plan year. Review elections annually for accuracy.
Watch for: Employees who participate in two employers’ FSA plans in the same year (e.g., after changing jobs). The annual limit is per person, not per employer. Employees are responsible for tracking this, but a reminder during enrollment helps.
Mistake #9: Poor Employee Communication
What happens: The plan exists, but employees don’t understand it. They don’t know what a Section 125 plan is, what benefits are available, or how to make elections. Participation rates are low.
The consequence: Low participation means less tax savings — for the employees who don’t enroll and for the employer (less FICA savings). It can also contribute to nondiscrimination testing failures if highly compensated employees participate at higher rates than rank-and-file employees.
How to avoid it:
- Explain benefits in plain English, not legal jargon
- Show employees the actual dollar impact on their paycheck (before and after pre-tax deductions)
- Hold enrollment meetings — in person or virtual — where employees can ask questions
- Provide materials in multiple languages if your workforce requires it
- Send reminders before open enrollment, during enrollment, and as the deadline approaches
- Offer FSA planning tools so employees can estimate the right contribution amount
Mistake #10: Not Reviewing the Plan Annually
What happens: The plan was set up three years ago and nobody has looked at it since. IRS limits have changed, the company has added new benefits, the workforce composition has shifted — but the plan document and administration haven’t kept up.
The consequence: The plan document doesn’t match actual practice. FSA limits in the system may be outdated. Nondiscrimination testing may not reflect current employee data. Benefits that were added or removed aren’t reflected in the plan document.
How to avoid it: Conduct an annual plan review — ideally 2–3 months before the plan year renewal. Check:
- Are IRS limits updated (FSA, DCAP, HSA)?
- Does the plan document reflect current benefits offerings?
- Has the employee population changed in ways that affect eligibility or testing?
- Is the plan administrator information current?
- Have any regulatory changes occurred that require plan amendments?
- Are carrier and TPA agreements current?
Most TPAs include an annual review as part of their service. If yours doesn’t, request one — or find a TPA that does.
The Consequences at a Glance
| Mistake | Potential Consequence |
|---|---|
| No plan document | Back taxes + penalties on all pre-tax deductions |
| Skipped testing | HCE benefits reclassified as taxable |
| Retroactive adoption | Invalid pre-tax deductions for retroactive period |
| Improper mid-year changes | Plan disqualification risk |
| Excluding eligible employees | Nondiscrimination failure + legal liability |
| Not tracking life events | Employee coverage gaps + employer liability |
| Ignoring FSA COBRA | $110/day penalty per affected individual |
| Exceeding contribution limits | Excess amounts taxable + W-2 errors |
| Poor communication | Low participation + testing failures |
| No annual review | Outdated plan document + compliance drift |
How to Audit Your Plan
If you’re not sure whether your plan has any of these issues, here’s a quick self-audit:
- Pull your plan document. When was it last updated? Does it match what you’re actually doing?
- Check your nondiscrimination testing. When was it last performed? What were the results?
- Review your enrollment process. Is every eligible employee offered the plan? Are qualifying life events tracked?
- Verify contribution limits. Are your systems configured with current IRS limits?
- Check COBRA procedures. Does your COBRA process include FSA participants?
- Look at participation rates. Are they consistent across employee groups, or heavily skewed toward higher earners?
If any of these checks reveal gaps, address them now. The cost of fixing a problem proactively is almost always lower than the cost of discovering it during an audit.
Learn about what makes a compliant plan in Section 125 Plan Document Requirements, and for an overall understanding of what to do annually, read What to Expect in Your First Year of Section 125.
Check your plan’s compliance status. Talk to David to identify potential issues before they become problems.
This guide is for informational purposes and does not constitute tax or legal advice. Consult with a qualified tax professional or benefits advisor for guidance specific to your situation.
