Medicare and HSA rules collide the moment you turn 65 and keep working. Most people assume the two accounts can coexist. They cannot. Once Medicare coverage begins, your HSA contribution limit drops to zero for every month you are enrolled. The trap is that premium-free Part A can start retroactively — up to six months before you sign up. Contributions made in good faith during those months become excess contributions.
This guide explains how medicare and HSA timing works, which forms you file, who signs them, and what the penalties cost. It describes the process. It is not tax or legal advice.
The Rule Behind Medicare And Hsa
Everything starts with employer size. If your employer has 20 or more employees, the group health plan pays first and Medicare pays second. That is the Medicare Secondary Payer rule. If your employer has fewer than 20 employees, Medicare generally pays first and the group plan pays second.
That single fact drives your whole decision. Medicare explains the working-past-65 basics here: Working past 65 (Medicare.gov).
The medicare and HSA conflict comes from IRS eligibility rules, not from Medicare itself. To contribute to an HSA you must be covered by a qualifying high deductible health plan and have no other disqualifying coverage. Medicare is disqualifying coverage. Part A alone is enough to disqualify you.
IRS Publication 969 states the rule plainly: beginning with the first month you are enrolled in Medicare, your contribution limit is zero. Read it here: Publication 969, Health Savings Accounts (IRS.gov).
Now add the lookback. If you apply for Part A more than six months after turning 65, coverage is backdated six months — but never earlier than the month you first became eligible. CMS describes retroactive entitlement here: Original Medicare (Part A and B) Eligibility and Enrollment (CMS.gov).
So the medicare and HSA problem is a calendar problem. Your enrollment date is not the date your coverage started. Six months of contributions can retroactively become excess.
Your Choices at 65
You have three practical paths. Delay all of Medicare and keep contributing. Take Part A only and stop contributing. Or take Part A and Part B and stop contributing. Which one is available depends on employer size and whether you have claimed Social Security.
One point is not optional. If you are already receiving Social Security retirement benefits, you are enrolled in Part A automatically and cannot simply decline it. Social Security explains the timing here: When to sign up for Medicare (SSA.gov).
| Your situation | Who pays first | What to do |
|---|---|---|
| Employer with 20+ employees, still actively working | Group health plan pays first; Medicare second | You may delay Part A and Part B. Delaying Part A keeps HSA contributions allowed. Confirm plan status in writing with your benefits administrator. |
| Employer with fewer than 20 employees | Medicare pays first; group plan second | Enroll in Part A and Part B at 65 in most cases. Your plan may pay almost nothing otherwise. HSA contributions must stop the month Medicare begins. |
| Already receiving Social Security benefits | Depends on employer size | Part A is automatic and cannot be refused while you draw benefits. HSA contributions must stop. Ask Social Security what withdrawing Part A would require. |
| COBRA or retiree coverage only | Medicare pays first | This is not coverage based on current employment. Enroll during your Initial Enrollment Period. HSA contributions must stop when Medicare begins. |
| Spouse’s HSA, you are on Medicare | Not applicable | Your own contributions stop. A spouse who is still HSA-eligible may contribute to their own account. Confirm the family limit with your tax preparer. |
The 2026 HSA limits are $4,400 for self-only coverage and $8,750 for family coverage, per IRS Revenue Procedure 2025-19. The age-55 catch-up adds $1,000. Your medicare and HSA limit is prorated monthly, so partial-year eligibility means a partial-year limit.
The Penalty If You Get It Wrong
There are three separate penalties. They stack, and two of them last for life.
The Part B late enrollment penalty adds 10% to your monthly premium for each full 12-month period you could have had Part B but did not enroll. The 2026 standard Part B premium is $202.90. Two full years late means a 20% penalty — roughly $40.58 per month added, every month, for as long as you have Part B.
The Part D late enrollment penalty is 1% of the national base beneficiary premium for each full uncovered month without creditable drug coverage. The 2026 national base beneficiary premium is $38.99. Thirty uncovered months equals 30% of $38.99, about $11.70 per month, rounded to the nearest ten cents.
That Part D figure is recalculated each year as the base premium changes. Details: Part D late enrollment penalty (Medicare.gov) and Avoid late enrollment penalties (Medicare.gov).
The third penalty is the tax one. Excess HSA contributions carry a 6% excise tax under Internal Revenue Code section 4973. It applies every year the excess stays in the account. You report contributions on Form 8889 and the excise tax on Form 5329.
The medicare and HSA excise tax is the one you can still fix. Withdraw the excess and any earnings on it by the due date of your return, including extensions, and the excise tax generally does not apply. See Instructions for Form 5329 (IRS.gov).
Medicare And Hsa: the Paperwork
Two forms do the work when you enroll in Part B after 65.
Form CMS-40B, Application for Enrollment in Medicare Part B. You complete and sign this one. Get it here: Form CMS-40B (CMS.gov).
Form CMS-L564, Request for Employment Information. Section A is yours. Section B must be completed and signed by your employer or group health plan administrator. It certifies your employment dates and your group coverage dates. Get it here: Form CMS-L564 (CMS.gov).
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Submit both to your local Social Security office by mail or fax, or apply online: Sign up for Part B only (SSA.gov). Ask for a date-stamped copy of everything you send.
Deadlines matter more than the forms. Your Initial Enrollment Period is seven months — the three months before your 65th birthday month, that month, and the three months after. The Part B Special Enrollment Period runs eight months from the end of employment or the end of group coverage, whichever comes first.
The drug coverage window is shorter. You generally have two months after creditable coverage ends to join a Part D or Medicare Advantage drug plan. If you miss both windows, the General Enrollment Period runs January 1 through March 31. See When does Medicare coverage start? (Medicare.gov).
The Traps People Fall Into
COBRA is the biggest one. COBRA is not coverage based on current employment. It does not protect your Part B Special Enrollment Period. People stay on COBRA for 18 months, then discover the SEP clock started when active employment ended.
Retiree coverage has the same problem. It also usually is not current employment coverage. Ask your former employer in writing whether it is creditable for Part D.
The small employer trap is quieter. Under 20 employees, Medicare is primary. If you skip Part B, your group plan may pay only what it would have paid as secondary. You could owe the rest yourself.
The last medicare and HSA trap is the last-month rule. If you used it to contribute a full year’s amount while eligible only in December, there is a testing period. Enrolling in Medicare during that period can trigger income and an additional 20% tax. Confirm your own numbers with a tax professional.
One thing works in your favor. After 65, HSA money already in the account can be used tax-free for Part B, Part D, and Medicare Advantage premiums. Medigap premiums generally do not qualify. You can spend the balance even though the medicare and HSA rules stop you from adding to it.
Frequently Asked Questions
Can I keep my HSA after enrolling in Medicare?
Yes. You keep the account and can spend the balance on qualified expenses tax-free. You simply cannot contribute for any month you are enrolled in Medicare, including retroactive months.
How far back does the lookback go if I enroll at 67?
Part A is backdated six months, but never earlier than the first month you were eligible. Verify your exact entitlement date on your Social Security award letter before amending anything.
Who signs Form CMS-L564?
Your employer or group health plan administrator signs Section B. You complete Section A. Social Security will not accept the medicare and HSA related SEP claim without that employer signature.
What if my employer refuses to complete CMS-L564?
Social Security may accept alternative proof, such as pay stubs, W-2s, or written plan documents showing coverage dates. Call 1-800-772-1213 and ask what evidence your local office will accept in your specific case.
Key Takeaways: Medicare And Hsa
- Employer size decides everything. Whether medicare and hsa is a choice or a requirement turns on the 20-employee rule.
- Part A is usually free. Most people take it at 65 even when medicare and hsa lets them delay Part B.
- Except with an HSA. Part A ends HSA contributions, the one case where medicare and hsa means delaying Part A too.
- COBRA does not count. For medicare and hsa, COBRA is not active employer coverage, and assuming otherwise creates a lifetime penalty.
Compare Your Options
Once you know what medicare and hsa means for you, the official Plan Finder shows what is actually sold in your ZIP code, and a SHIP counselor will walk it with you for free — no commission, no sales call.
Official Sources & Resources
- Social Security — Medicare enrollment: https://www.ssa.gov/medicare
- IRS Publication 969 (HSAs): https://www.irs.gov/publications/p969
- Medicare.gov: https://www.medicare.gov
- CMS.gov: https://www.cms.gov
- Find your SHIP counselor: https://www.medicare.gov/talk-to-someone
Checked against the official sources above in September 2026. Rules and dollar figures change; if a notice you received disagrees with this page, the notice wins — and please tell us. General information, not legal, financial or medical advice.