HSA Edge Cases: 10 IRS Rules Most Articles Get Wrong

IRS authority

Qualified medical expenses are those incurred after the HSA is established.

Detailed explanation

This is the load-bearing rule for the shoebox strategy and the single most frequently misunderstood HSA rule. Most blog posts and forum threads claim there is some implicit time limit on retroactive reimbursement - three years, seven years, ten years. There is not. The only timing requirement is that the medical expense was incurred AFTER the HSA was established. A receipt from 25 years ago can be reimbursed today, tax-free, as long as the HSA existed when the expense happened and the documentation survives. Documentation requirement: receipt or Explanation of Benefits showing the date of service, dollar amount, provider name, and medical nature of the expense.

IRS authority

An eligible individual cannot be covered by any health plan that is not a high deductible health plan, with limited exceptions. A general-purpose health FSA is considered other health coverage and disqualifies HSA contributions, including a spouse's FSA where the employee can be reimbursed for the spouse's medical expenses.

Detailed explanation

A general-purpose FSA pays first-dollar medical expenses for the household. The IRS treats this as disqualifying coverage for BOTH spouses, even if only one is enrolled in the FSA, because the FSA can be used to reimburse the non-enrolled spouse's medical expenses. This catches a lot of dual-income households at open enrollment, especially when one spouse's employer auto-enrolls in an FSA by default. The two compatible alternatives are a limited-purpose FSA (restricted to dental and vision only - explicitly compatible per IRS rules) and a dependent-care FSA (restricted to childcare - explicitly compatible because it does not reimburse medical expenses).

IRS authority

An individual who is an eligible individual during the last month of the taxable year is treated as having been an eligible individual during every month during such taxable year, subject to a testing period requirement.

Detailed explanation

Two options when HDHP coverage starts mid-year: (a) prorate the contribution by the number of months you were HSA-eligible (safe, no testing-period obligation), or (b) use the last-month rule to contribute the full annual cap, accepting the obligation to stay HSA-eligible all of the next calendar year. Worked example: HDHP coverage starts October 1, 2026. Last-month rule lets you contribute the full $4,400 self-only cap for 2026 IF you stay HSA-eligible through December 31, 2027. If you switch to a non-HDHP plan in June 2027, the excess (10 months worth) gets recaptured as ordinary income plus a 10% additional tax. The safer alternative is proration: 3 months of eligibility times one-twelfth of the annual cap equals $1,100 contribution, no testing-period obligation.

IRS authority

“If there is clear and convincing evidence that amounts were distributed from an HSA because of a mistake of fact due to reasonable cause, the account beneficiary may repay the mistaken distribution no later than April 15 following the first year the account beneficiary knew or should have known the distribution was a mistake.”

Detailed explanation

Common scenarios that qualify as mistaken distributions: HSA debit card swiped at the wrong merchant, bookkeeping error reimbursing an expense that was already reimbursed, automatic withdrawal coded against the wrong account. Most HSA custodians (Fidelity, Lively, HSA Bank) have a written mistaken-distribution recovery process - call the custodian, document the error in writing, and return the funds before April 15. The custodian typically updates Form 1099-SA to reflect the corrected withdrawal. Form 8889 does not require special reporting for properly-corrected mistaken distributions. Keep a paper trail showing the original error and the timely repayment.

IRS authority

“Medical expenses are the costs of diagnosis, cure, mitigation, treatment, or prevention of disease, and the costs for treatments affecting any part or function of the body.”

Detailed explanation

The eligibility test under IRC 213(d) is the nature of the care, not the geographic location of the provider. Common cross-border scenarios that qualify: dental tourism in Mexico or Costa Rica, bariatric surgery abroad, IVF in countries with lower costs, cancer treatment at international centers, prescription medications filled at a foreign pharmacy with a valid prescription. The documentation requirements are identical to domestic care: receipt or Explanation of Benefits showing date, amount, provider, and medical nature. Currency conversion documentation (exchange rate on date of payment) is helpful for audit defense but not strictly required - the dollar amount paid is what matters. Two narrow exclusions remain: cosmetic procedures (same exclusion as domestic), and illegal-in-the-US treatments (also excluded domestically).

IRS authority

Distributions from an HSA used to pay for health coverage are not qualified medical expenses, except in the case of: (i) coverage under a health plan during a period in which the individual is receiving unemployment compensation, (ii) qualified long-term care insurance, (iii) COBRA continuation coverage or any health plan during any period of continuation coverage required under any federal law, and (iv) for individuals over age 65, Medicare Part B, Part D, and Medicare Advantage premiums (but not Medigap).

Detailed explanation

The four exceptions to the no-premiums rule: (1) COBRA or any federal continuation coverage, (2) qualified long-term care insurance (subject to age-based annual caps), (3) Medicare Part B, Part D, and Medicare Advantage premiums after age 65 (Medigap supplemental policies are NOT included), (4) health insurance while receiving unemployment compensation. A common pattern: job change with a 1-3 month gap, elect COBRA HDHP coverage for the bridge, pay the COBRA premium tax-free from the HSA. Bonus: COBRA HDHP coverage also keeps you HSA-eligible to make NEW contributions during the COBRA window. The premium itself is HSA-reimbursable AND the underlying HDHP keeps the HSA eligibility intact.

IRS authority

A high deductible health plan means a health plan with an annual deductible not less than the statutory minimum and with annual out-of-pocket expenses not exceeding the statutory maximum.

Detailed explanation

Many ACA bronze plans qualify as HDHPs, but not all. Some bronze plans have deductibles too low to meet the IRS minimum. Others have copay structures (small-dollar copays for primary care visits before the deductible) that disqualify them because the IRS rule requires the deductible to apply to ALL medical care other than preventive services. Always pull the Summary of Benefits and Coverage (SBC) document from your plan and verify the two numbers explicitly: deductible meets the IRS minimum for your coverage tier, and the out-of-pocket cap stays at or below the IRS maximum. r/Fire PSA threads on this topic regularly hit the front page because the marketplace's HSA-eligible flag is reliable but not infallible.

IRS authority

You must keep records sufficient to show that the distributions were exclusively to pay or reimburse qualified medical expenses, that the qualified medical expenses had not been previously paid or reimbursed from another source, and that the medical expenses had not been taken as an itemized deduction in any year.

Detailed explanation

The four data points that must appear on any documentation that survives an audit: (1) date of service - establishes the expense was incurred AFTER the HSA was opened, (2) dollar amount paid - establishes the reimbursement did not exceed the expense, (3) provider name - establishes the source was a qualified medical provider, (4) medical nature of the expense - establishes the expense qualifies under IRC 213(d). Credit card statements alone are insufficient because they show the date and amount but not the medical nature. Best practice: keep both the itemized receipt and the EOB. Digital scans are fine. Annotate the medical nature directly on the receipt image if it is not already obvious. Audit reality: low rate (HSAs are audited less frequently than other tax positions), but bad outcomes when audited badly (the reimbursement gets reclassified as a non-qualified distribution with ordinary income tax plus a 20% additional tax for under-65 holders).

IRS authority

You can include in medical expenses amounts you pay to lose weight if it is a treatment for a specific disease diagnosed by a physician (such as obesity, hypertension, or heart disease). You cannot include the cost of a weight-loss program if the purpose is to improve general health or appearance.

Detailed explanation

Two IRS rules combine for GLP-1 HSA coverage. The prescription-medicines rule under IRC 213(d) covers the GLP-1 medication itself when prescribed by a physician. The weight-loss-program rule under IRS Publication 502 covers the weight-loss program when prescribed for a specific diagnosed disease. If both rules are satisfied via the prescription plus diagnosis chart note, no separate LMN is required. An LMN strengthens documentation in three specific scenarios: (a) gray-area conditions where the diagnosis is borderline (BMI 26 with mild comorbidities), (b) HSA debit card declines at checkout (some retailers' IRS-approved expense lists flag GLP-1s for additional documentation), (c) audit defense in jurisdictions or cases where the IRS examiner scrutinizes the medical-nature requirement closely. The LMN typically includes the diagnosis code, the medical necessity for the prescription, and the prescribing clinician's signature.

IRS authority

In the case of a health savings account, a tax equal to 6 percent of the amount of the excess contributions to such account is imposed for each taxable year the excess contributions remain in the account.

Detailed explanation

Common scenarios that produce excess HSA contributions: (a) employer contributed plus employee contributed, the combined total exceeded the cap, (b) spouse's FSA was discovered mid-year and retroactively disqualified prior contributions, (c) family-to-self-only HDHP change mid-year with the wrong proration calculation, (d) miscalculated catch-up contribution (the $1,000 catch-up requires age 55+ AND HSA eligibility for the contribution year). Form 5329 has dedicated lines for excess HSA contributions. The withdrawal of the excess includes the earnings on the excess - both the principal excess and the attributable earnings are taxable in the year of correction. Timing matters: the deadline is the tax-filing deadline including extensions, so a timely-filed extension to October 15 extends the correction window. After the deadline, the 6% excise tax compounds annually until the excess is withdrawn or absorbed by under-contributing in a future year (rare but possible).

See edge case 2 (spouse FSA disqualification) for the upstream rule that triggers scenario (b) above.