When your FSA administrator sends an audit letter, you generally have 30 to 90 days to submit an Explanation of Benefits or an itemized receipt proving the charge was a qualified medical expense. FSA audit documentation has to come from an independent third party — your provider, insurer, or pharmacy — and show the patient, date, service or product, and the amount you actually owed. A credit card slip or bank statement alone will not clear the review. Miss the deadline or fail to document the charge, and the money loses its tax-free status and gets added back to your W-2 wages.
What Documents Will Actually Clear the Audit
The paperwork your administrator wants depends on what you bought. Getting this right on the first submission saves weeks. A receipt showing you paid a certain dollar amount is almost never enough on its own, because it proves payment but not what the payment was for.
Medical, Dental, and Vision Services
For any service that ran through your health insurance, the strongest document is the Explanation of Benefits your insurer issues after processing the claim. The EOB needs to show the patient’s name, the date of service, a description of what was done, and the specific dollar amount you owe after insurance paid its share. That last figure is the one administrators care about most, because it proves the expense was not covered by another source.
If you have no insurance or the service was not covered, ask the provider for an itemized statement with the same details: patient, date, description, and amount charged. A statement showing only a total balance due, without breaking out the services, will be rejected.
Over-the-Counter Products
For OTC drugs and medicines, submit an itemized receipt showing the store name, the specific product name, the purchase date, and the price.1FSAFEDS. FAQs – What Documentation Do I Need to Submit to Be Reimbursed for Eligible Over-the-Counter Drugs and Medicines A register tape that says only “pharmacy items” or “health and beauty” will not pass. The product name has to be visible. Since the CARES Act, most OTC medications no longer require a prescription for FSA eligibility, but a few categories still do.
Items That Require a Letter of Medical Necessity
Some expenses are only eligible if a doctor confirms they treat a specific medical condition. This applies to items like a specialized mattress, an air purifier, or a gym membership tied to a diagnosed condition. Your doctor’s Letter of Medical Necessity has to identify the diagnosis, explain why the item is medically required, and state how long you need it.2FSAFEDS. Letter of Medical Necessity Form A vague note saying something “is medically necessary” without linking it to a specific condition and treatment plan will not clear review.
Medical Mileage and Travel
Transportation to and from medical appointments is eligible, including mileage in your own car, parking, tolls, and public transit fares. The IRS standard rate for medical driving is 20.5 cents per mile for 2026.3Internal Revenue Service. IRS Sets 2026 Business Standard Mileage Rate at 72.5 Cents per Mile, Up 2.5 Cents Substantiate mileage with a log showing the date, destination, purpose of the trip, and miles driven. Keep receipts for parking and tolls.
Orthodontia
Orthodontia is its own case because treatment often spans multiple plan years. If you paid the orthodontist a lump sum and are seeking reimbursement across plan years, submit the payment receipt, documentation from the provider confirming the patient is still in active treatment, and a record of what you were reimbursed in prior years.4FSAFEDS. Orthodontia Quick Reference Guide
If you set up recurring monthly payments instead, the orthodontia service contract itself becomes the key document. That contract must include the provider’s name, the patient’s name, a description of the treatment, the payment schedule with dates, and the monthly amount. Recurring payment arrangements usually need to be re-established each plan year, since they do not automatically carry over.4FSAFEDS. Orthodontia Quick Reference Guide
How to Submit Your Response
The verification notice lists the specific claim dates and dollar amounts your administrator needs documented, plus a response deadline. That deadline is firm. Most plans give somewhere between 30 and 90 days, and missing it produces the same outcome as failing the review: the money gets clawed back.
Upload documents through your plan’s online portal when one is available. Each file should be clear and legible, saved as a PDF or JPEG. If you have to fax or mail physical copies, send them by certified mail with return receipt requested so you can prove you submitted on time. Most administrators will not accept documents by regular email because of privacy rules.
After you submit, the administrator either approves the claim, making the provisional charge final, or denies it as ineligible or insufficiently documented. Review times vary by plan and volume. If you haven’t heard back in a few weeks, check the portal or call.
Why the Standard Is This Strict
Under Proposed Treasury Regulation 1.125-6, every FSA claim has to be substantiated by an independent third party. Plans cannot sample, cannot waive review for small charges, and cannot let you self-certify that an expense was medical.5Internal Revenue Service. IRS Chief Counsel Advice 202317020 The documentation has to come from someone other than you, your spouse, or your dependents. If the plan slips on substantiation, it can lose its qualification under Section 125, and the tax benefits vanish for everyone enrolled. That is why the request landed in your inbox even when the charge looks obviously medical to you.
If Your FSA Card Gets Suspended
Miss the deadline and your FSA debit card will likely be deactivated. Some plans send a warning notice first, giving you a short window (often around 10 days) to respond before the card is shut off. Once deactivated, you cannot use the card for new purchases until the outstanding issue is resolved.
You have three ways to clear a suspension: submit the missing documentation, repay the unsubstantiated amount directly, or let the plan offset the balance against future valid claims. With offset, the administrator deducts what you owe from the next properly documented claim. If you owe $100 from an unsubstantiated charge and later submit a valid $300 claim, you receive $200. Once the balance is cleared, the card is typically reactivated.
How to Appeal a Denied Claim
A denial is not the end. FSA plans offered through an employer fall under ERISA, which gives you the right to formally appeal an adverse benefit determination. Federal regulations require the plan to allow at least 180 days from the date you receive the denial notice to file an appeal.6eCFR. 29 CFR 2560.503-1 – Claims Procedure
Your appeal should include a written explanation of why you believe the claim is eligible, plus any supporting documentation you did not submit the first time. If the denial was for insufficient paperwork, this is your chance to fill the gap. A new or more detailed Letter of Medical Necessity can replace an original that was too vague.
Once you file, the plan has to decide within a set time. For post-service claims, which covers most FSA verification disputes, the plan has no more than 60 days to respond if it provides one level of appeal.6eCFR. 29 CFR 2560.503-1 – Claims Procedure If the plan offers two levels of appeal, each level gets 30 days. Read the denial notice carefully before responding: it must state the specific reason for denial and explain the appeal procedure.
What It Costs You If the Claim Stays Unsubstantiated
If you cannot substantiate a claim and do not repay the money, the unsubstantiated amount loses its tax-free status. Your employer is required to add it to your taxable wages, and it will appear on your W-2 as additional income. You then owe federal income tax, applicable state income tax, and potentially Social Security and Medicare taxes on that amount. This happens even when the expense was genuinely medical and you simply cannot produce the right paperwork.
Before it reaches that point, the plan will typically walk through correction steps set out in Proposed Treasury Regulation 1.125-6.5Internal Revenue Service. IRS Chief Counsel Advice 202317020 The employer demands repayment first. If you do not repay, the plan can offset against future claims or withhold from your pay. Only after those options are exhausted does the amount get reported as taxable income. Which is why responding on time, with the right document, is worth the hour it takes to pull an EOB or call your provider for an itemized statement.