66-Year-Old Discovers Filing for Social Security Made His HSA Contributions Illegal

A 66-year-old still working, covered by his employer’s high-deductible health plan (HDHP), maxes his health savings account including the age-55 catch-up. He files for Social Security. Weeks later he gets a Medicare card with a Part A start date six months earlier than his filing date. That backdated enrollment turned his last six months of HSA contributions into excess contributions, and the IRS charges 6% of the excess amount every year it stays in the account.

This trap catches thousands of working seniors. It involves two decisions people usually make separately: when to claim Social Security and how to fund an HSA.

Once you are past 65, filing for Social Security triggers automatic enrollment in Medicare Part A. The Social Security Administration applies that Part A coverage retroactively up to six months (never earlier than the month you turned 65). Anyone enrolled in Medicare, including Part A only, is barred from making new HSA contributions. The IRS treats every dollar contributed during that retroactive window as an excess contribution.

Your employer’s payroll system and HSA custodian do not know this. Your benefits portal will happily let you keep contributing right up to the day you sign the Social Security application, and for six months before it.

The dollar stakes are real. For 2026, family HDHP coverage carries an annual deductible floor of $5,850 and an out-of-pocket ceiling of $10,700. Add the $1,000 catch-up available at 55 and the six-month excess can easily run into several thousand dollars.

How the 6% Excise Tax Actually Bites

The excise tax applies every year the excess stays in the HSA. Leave it there for a decade and the government takes 6% of that excess annually until you withdraw it. If you catch it in time, there is a clean fix. Before the tax filing deadline (including extensions) for the year the excess was contributed:

1. Call the HSA custodian and specifically request a removal of excess contribution. The paperwork code matters. An ordinary distribution will not fix the problem.
2. Withdraw the excess dollars plus earnings attributable to them. The custodian calculates the earnings figure.
3. Report those earnings as taxable income in the year you take them out. That is far cheaper than a recurring 6% penalty.
4. If excess dollars were already spent on qualified medical bills, hire a tax professional. The unwind depends on what was reimbursed and when.

If you are working past 65 and plan to file for Social Security, stop HSA contributions six full months before the month your Part A coverage begins. Practically, if you want to file in October, your last HSA contribution should be for April. Coordinate with payroll, because most systems will keep deducting until you say stop. If you are still deciding when to claim, remember the 2027 Social Security COLA is currently tracking toward 3.1%, which is modest and does not justify claiming earlier than your plan calls for.

Why the HSA Is Still the Best Account You Own

The trap is annoying. The account is extraordinary. Contributions go in pre-tax, growth is tax-free, and qualified withdrawals are tax-free, a combination no other retirement vehicle offers. After 65 you can use HSA dollars tax-free for Medicare Part B, Part D, and Medicare Advantage premiums, which matters when the standard 2026 Part B premium runs $202.90 a month and high earners pay more. Medigap premiums are the one exclusion.

The quiet superpower: There is no deadline on reimbursing yourself. Pay medical bills out of pocket for years, keep receipts, and reimburse yourself decades later while the HSA compounds untouched. That turns an HSA into a stealth Roth.

If you are still working and undecided on claiming, treat the HSA-Medicare interaction as a scheduling problem. Pick a Social Security start month, count back six months, and set your contribution stop date on the calendar before you sign anything.

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