HSA eligibility
To contribute to an HSA you must (1) be covered by a high-deductible health plan (HDHP) on the first day of the month, (2) have no other non-HDHP coverage (with a few exceptions for limited-purpose FSAs, accident, dental, vision, long-term care), (3) not be enrolled in Medicare, and (4) not be claimed as a dependent on another's return.
HDHP definition
For 2024 an HDHP has a minimum deductible of $1,600 self-only / $3,200 family and an out-of-pocket maximum of $8,050 self-only / $16,100 family. Limits are indexed annually. Some preventive care can be covered before the deductible without disqualifying the plan.
Health FSA
A health flexible spending arrangement is a use-it-or-lose-it employee benefit funded by salary reductions. Annual contribution limit is set yearly. Employers may offer a $640 carryover (2024) or a 2.5-month grace period, but not both. Health FSAs disqualify HSA contributions unless they are limited-purpose (dental and vision only).
HRA
A health reimbursement arrangement is funded entirely by the employer. QSEHRA (Qualified Small Employer HRA) lets businesses with fewer than 50 employees reimburse individual market premiums and medical expenses up to an annual limit. ICHRA (Individual Coverage HRA) is available to employers of any size and lets employees buy their own coverage with employer-funded reimbursements.
Archer MSA
Archer Medical Savings Accounts are a closed predecessor to HSAs. Few new Archer MSAs are established today, but existing accounts continue to receive favorable tax treatment.
What the publication does not say
IRS publications are summaries, not the law. They do not cite every controlling regulation, and they routinely omit edge cases that would make the discussion harder to read. For close calls, escalate from the publication to the underlying Internal Revenue Code section, the related Treasury regulations, the relevant revenue rulings or revenue procedures, and (if the dollars warrant) the leading court cases. The IRS-published Internal Revenue Manual and the Audit Techniques Guides — also free on IRS.gov — provide the agency's internal procedural perspective, which often clarifies how the publication's rules play out in an examination.