IRS Rules Governing FSAs

Flexible Spending Accounts are governed by a dense body of Internal Revenue Service rules that determine who may participate, how much may be contributed, which expenses qualify for reimbursement, and what happens to unspent funds. These rules derive primarily from Internal Revenue Code Section 125, which authorizes cafeteria plans, and Section 106, which excludes employer-provided health coverage from gross income. Understanding the IRS framework is essential for both employers designing benefit plans and employees making enrollment elections, because violations can trigger retroactive taxation and plan disqualification.

Definition and scope

A Flexible Spending Account is a tax-advantaged benefit arrangement offered through an employer's cafeteria plan under IRC Section 125. The IRS recognizes two primary FSA variants with distinct regulatory treatment:

A third variant — the Limited Purpose FSA — is restricted to vision and dental expenses, making it compatible with simultaneous HSA participation (IRS Publication 969).

The regulatory framework governing FSAs appears primarily in:

All FSAs must be offered through an employer; self-employed individuals, sole proprietors, and partners in a partnership are ineligible to participate under IRC § 125(d)(2).

How it works

FSA participation follows a structured annual cycle governed by IRS timing and election rules.

  1. Open enrollment election: Employees elect an annual contribution amount during the employer's open enrollment period. This election is irrevocable for the plan year except under circumstances the IRS defines as a qualifying life event (marriage, divorce, birth, adoption, or a change in employment status affecting coverage eligibility) per Treasury Regulation § 1.125-4.

  2. Pre-tax payroll reduction: Elected amounts are withheld from each paycheck before federal income tax, Social Security tax (FICA), and Medicare tax are calculated. This reduces the employee's taxable wages for the year.

  3. Employer funding of Health Care FSAs: For HCFSAs specifically, the IRS requires that the full annual elected amount be available for reimbursement from day one of the plan year — not just the portion already withheld. This "uniform coverage" rule is codified in Treasury Regulation § 1.125-5(d).

  4. Reimbursement and substantiation: Expenses must be substantiated. The IRS requires documentation — typically an Explanation of Benefits or itemized receipt — confirming the expense is an eligible medical cost as defined under IRC § 213(d). FSA debit card transactions must meet auto-adjudication or third-party substantiation standards per IRS Notice 2006-69.

  5. Plan year close and forfeiture: Unspent balances generally forfeit under the use-it-or-lose-it rule codified in Treasury Regulation § 1.125-5(c). Employers may adopt one of two IRS-permitted relief options (detailed below), but neither is mandatory.

The annual contribution limit for Health Care FSAs is set by IRS Revenue Procedure adjustments each fall. For 2024, the IRS set the limit at $3,200 per employee (IRS Revenue Procedure 2023-34). Dependent Care FSA limits are set by statute at $5,000 per household (or $2,500 for married individuals filing separately) under IRC § 129(a)(2) and are not subject to annual inflation adjustment.

Common scenarios

Scenario 1 — Grace period plan: An employer adopts a 2.5-month grace period under IRS Notice 2005-42. An employee with $400 remaining at December 31 has until March 15 of the following year to incur eligible expenses and drain the balance. Expenses incurred in January and February of the new plan year are reimbursed against the prior year's unused funds first.

Scenario 2 — Carryover plan: Under IRS Notice 2013-71 (as updated by IRS Notice 2020-33), an employer instead permits a carryover of up to $640 (the 2024 indexed limit, equal to 20% of the HCFSA contribution ceiling) into the next plan year. Carryover funds do not count against the following year's contribution limit. Employers may not offer both a grace period and a carryover simultaneously.

Scenario 3 — Mid-year HSA transition: An employee enrolled in a Health Care FSA changes coverage mid-year to a High-Deductible Health Plan and wishes to open an HSA. IRS rules prohibit HSA contributions while a general-purpose HCFSA is active. The employee must either spend down the FSA balance by year-end or transition to a Limited Purpose FSA to preserve HSA eligibility per IRS Publication 969.

Scenario 4 — Dependent Care FSA earned income limit: A married couple with a combined income of $60,000 and a DCFSA election of $5,000 discovers that one spouse earned only $3,800 during the year. Under IRC § 129(b), the excludable DCFSA benefit cannot exceed the lesser spouse's earned income. The $1,200 excess is included in gross income and subject to tax.

Decision boundaries

Several IRS rules define categorical distinctions that determine eligibility and tax treatment.

Grace period vs. carryover — mutually exclusive options:

Feature Grace Period Carryover
Authorized by IRS Notice 2005-42 IRS Notice 2013-71
Time extension 2.5 months after plan year end Unused balance rolls to next year
Dollar cap None (full balance may be used) $640 (2024 limit, indexed annually)
HSA compatibility No — extends disqualification period No — carried balance disqualifies HSA
Employer adoption Optional Optional

HCFSA vs. DCFSA — distinct statutory authority:

Health Care FSAs operate under IRC § 125 and § 213(d). Dependent Care FSAs operate under IRC § 125 and § 129. These sections impose different income exclusion mechanics, different contribution ceilings, and different expense definitions. Mixing reimbursement categories — paying a childcare invoice from an HCFSA — violates IRS rules and makes the reimbursement taxable.

Termination mid-year: When an employee leaves employment, HCFSA and DCFSA rules diverge. HCFSA reimbursements are limited to the balance remaining in the account (if the employee has not yet used the full election, remaining unfunded amounts are forfeited to the employer). DCFSA reimbursements after termination are limited to expenses incurred before the termination date, per Treasury Regulation § 1.125-5(o).

The broader landscape of IRS health account regulations, including how FSA rules interact with HSA and HRA frameworks, is covered in the regulatory context for health savings resource. Employers and plan administrators seeking a comprehensive orientation to the tax-advantaged account ecosystem can reference the National Health Savings Authority home resource for structured navigation across account types and IRS rule sets.

References

The law belongs to the people. Georgia v. Public.Resource.Org, 590 U.S. (2020)