Medicare enrollment - including free Part A - immediately disqualifies you from making HSA contributions. The 6-month Part A retroactive lookback rule catches HSA contributors by surprise and can trigger IRS penalties. To keep contributing to your HSA past 65, you must delay all Medicare enrollment and avoid claiming Social Security.
Why HSAs and Medicare Don't Mix
If you contribute to a Health Savings Account (HSA), Medicare enrollment - even enrollment in only Part A - immediately disqualifies you from making further HSA contributions. This is one of the most expensive Medicare mistakes someone working past 65 can make.
The reason: HSAs require you to be enrolled in a High Deductible Health Plan (HDHP) and not enrolled in any other health coverage, including Medicare. Once Medicare kicks in, your HSA-eligibility ends. Period.
The 6-Month Part A Lookback Rule
Critical: When you finally enroll in Medicare Part A after age 65, Medicare retroactively backdates your Part A coverage by up to 6 months (but not earlier than your 65th birthday month). Any HSA contributions you made during that retroactive period are now disallowed and subject to IRS penalties.
Example: You turn 65 in March 2026. You continue working with HDHP coverage and contributing to your HSA. In December 2026, you decide to enroll in Medicare Part A. Medicare will backdate your Part A coverage to June 2026 (6 months before December). That means your HSA contributions for June through November 2026 are now subject to 6% excise taxes plus income tax on the excess contributions.
How to Avoid the HSA Trap
If you want to keep contributing to your HSA past age 65:
- Do NOT enroll in Medicare Part A. Yes, it's free for most people. But enrolling disqualifies you from HSA contributions.
- Stop collecting Social Security benefits if you haven't started yet. SSA enrolls you in Part A automatically when you take Social Security benefits.
- Stop HSA contributions 6 months before the date you plan to start Medicare or Social Security to avoid the lookback issue.
- You can still use existing HSA funds for qualified medical expenses, including Medicare premiums - just no new contributions.
What Counts as "Enrolled" in Medicare?
This is more subtle than you might think:
- Active enrollment in Part A or Part B = enrolled (HSA-ineligible)
- Eligible for Medicare but not enrolled = NOT enrolled (HSA-eligible)
- Receiving Social Security retirement benefits at 65+ = automatically enrolled in Part A (HSA-ineligible)
- Receiving Social Security Disability for 24 months = automatically enrolled in Parts A and B (HSA-ineligible)
Good news: If you've never enrolled in Medicare and aren't receiving Social Security, you can keep contributing to your HSA past age 65. Many people do this until age 70 or beyond.
Special Considerations for LANL and Sandia Employees
Many Los Alamos National Laboratory and Sandia National Laboratories employees have HSA-eligible HDHPs. If you plan to continue contributing past 65:
- Verify with HR that your specific plan qualifies as an HDHP
- Don't apply for Social Security retirement benefits
- Delay all Medicare enrollment until you stop HSA contributions
- Plan the 6-month "cooling off" period before retirement
What About the Free Part A Argument?
Some advisors recommend taking free Part A "just in case" since it provides hospital coverage at no premium cost. But this advice ignores HSAs entirely. The HSA tax benefits often far exceed the small benefit of having Part A as a secondary payer alongside your employer plan.
The math: HSA contributions reduce your taxable income immediately, grow tax-free, and come out tax-free for medical expenses. Maximum 2026 HSA contributions for a 65+ individual: $5,400 (single HDHP) or $9,750 (family HDHP) including catch-up. If you're in the 24% federal tax bracket, that's potentially $1,296-$2,340 in annual tax savings - far more than Part A's marginal benefit when you already have employer coverage.
Getting This Right Matters
The HSA-Medicare interaction is one of the most common areas where people make costly mistakes. A licensed Medicare agent who understands HSAs can help you time things correctly.
Frequently Asked Questions
Can I keep my HSA after enrolling in Medicare?
Yes. You can keep your existing HSA balance and use it for qualified medical expenses (including Medicare Part B premiums, Medicare Advantage premiums, and Part D premiums) tax-free. You just cannot make new contributions.
Does Medicare Part A enrollment really disqualify me from HSA contributions?
Yes. The IRS rules state that you must not be enrolled in any other health coverage besides an HDHP. Medicare Part A counts as "other health coverage" even though most people pay no premium for it.
What if I'm already collecting Social Security?
Once you collect Social Security at age 65+, SSA automatically enrolls you in Part A. You cannot easily decline Part A without giving up future Social Security benefits. If you want to keep contributing to your HSA, you generally need to defer Social Security.