If you have a Health Savings Account and you are approaching 65, there is one Medicare rule you absolutely have to understand. It is not advertised. Your HR department probably will not catch it. The IRS will not warn you in advance. But it can result in real tax penalties and lost contributions that you cannot get back.
I am a licensed Medicare broker in Mesa, and I have watched this rule blow up more than one client’s retirement plan. The fix is straightforward if you know about it ahead of time. The fix is much harder if you find out after you have already enrolled. So this article is the heads-up I wish more people got before they crossed into Medicare territory.
The Rule in One Paragraph
If you enroll in any part of Medicare, including premium-free Part A, you become ineligible to contribute to a Health Savings Account. Period. Even if you are still working. Even if you are still on a high-deductible health plan through your employer. Even if Part A is free and you signed up automatically. The IRS does not allow HSA contributions for anyone enrolled in Medicare.
That is the simple version. The wrinkle is that Medicare Part A enrollment is automatically backdated up to 6 months when you do enroll, but never earlier than your 65th birthday. So if you wait until age 67 to enroll in Medicare, your Part A start date is set retroactively to 6 months before your enrollment month. Any HSA contributions you made during those backdated 6 months are technically excess contributions, subject to a 6 percent excise tax every year they remain in the account.
This is the trap. Most people do not realize Medicare backdates Part A. They keep contributing to an HSA right up until they sign up for Medicare. Then they get hit with a tax bill they were not expecting.
How Backdating Actually Works
Let me give you a concrete example. Say you turn 65 on April 15, 2025, but you decide to keep working and contributing to your HSA through June 2026. In June 2026 you enroll in Medicare, with a start date of July 1, 2026.
Medicare looks at your enrollment date and backdates Part A coverage to January 1, 2026. That is 6 months before your July effective date. Any HSA contributions you made between January 1, 2026, and June 30, 2026, are now excess contributions because you were technically Medicare-eligible during that period.
The IRS treats those contributions as taxable income for the year you made them, plus a 6 percent excise tax for every year they remain in the account. To fix it, you have to withdraw the excess plus any earnings before the tax filing deadline. If you miss that deadline, the penalties stack up.
This is why anyone planning to keep contributing to an HSA past 65 has to plan their Medicare enrollment carefully. The cleanest path is to stop HSA contributions at least 6 months before you enroll in Medicare. That way the backdating window covers a period when you were not contributing, and there are no excess contributions to clean up.
The Most Common Way People Get Caught
The single most common scenario is people who turn 65 and assume that because they are still working, they do not need to think about Medicare. Then later they decide to enroll, often when they are about to retire, and they get blindsided by the backdating rule.
A close second is people who file for Social Security at 65 or before age 65 while still working. Filing for Social Security automatically enrolls you in Medicare Part A. If you were contributing to an HSA, your HSA eligibility ended the month your Part A started. Most people do not realize this and keep contributing for months or years before someone tells them.
A third scenario is the spouse who was covered under their working spouse’s HSA-eligible high-deductible plan. They turn 65, get auto-enrolled in Part A because they were already drawing Social Security, and the working spouse’s HSA contributions become problematic on the family contribution side.
If you are at all involved with an HSA, it is worth a 30-minute conversation with someone who knows the rules before you do anything Medicare-related. The cost of getting it right is zero. The cost of getting it wrong starts at a few hundred dollars and can climb into the thousands.
How to Plan for This Properly
There are basically three paths.
Path one is to stop HSA contributions at least 6 months before you enroll in Medicare. If you plan to enroll in Medicare on January 1 of the year you retire, your last HSA contribution should be no later than June of the previous year. This gives the backdating window a clean overlap with a period when you were not contributing.
Path two is to delay Medicare enrollment past your initial enrollment period. This requires having creditable coverage from a large employer plan, which lets you delay Part B without a penalty. The important detail is that you also have to actively decline Part A or refuse to file for Social Security, because filing triggers automatic Part A enrollment. Your HR department or a Medicare broker can confirm whether your situation supports this.
Path three is to enroll in Medicare on time and stop HSA contributions in advance, accepting that you are giving up some HSA contribution years. For people in their late 60s with already-significant HSA balances, this is often the right call.
The wrong move is to keep contributing to the HSA past 65 without thinking about Medicare. Whatever path you take needs to be deliberate.
What to Do With the HSA Money You Already Have
Even if you stop contributing, your existing HSA balance is still yours. After 65, you can use HSA funds for any expense without the 20 percent penalty that would have applied earlier. You will pay regular income tax on non-medical withdrawals, but you can spend the money on whatever you want.
Better yet, HSA funds can still be used tax-free for qualified medical expenses, including Medicare premiums. Medicare Part B, Part D, Medicare Advantage, and Long-Term Care Insurance premiums are all qualified medical expenses for HSA purposes. The one exception is Medigap supplement premiums, which the IRS does not consider qualified.
This means an HSA can be a powerful tool for retirees on Medicare. You stop contributing once you enroll, but the balance keeps working. You can pull money tax-free to pay your Part B and Part D premiums every month. For someone with a sizable HSA, that can cover the bulk of their Medicare premiums for years.
A Word on Spousal HSAs
If you and your spouse are both still working and one of you is on Medicare while the other is not, the rules get more nuanced. The Medicare-enrolled spouse cannot contribute to an HSA. The non-Medicare spouse can still contribute to an HSA in their own name as long as they have HSA-eligible coverage.
For families on a family HDHP, the non-Medicare spouse can still contribute up to the family limit if they are the account holder, even though their Medicare-enrolled spouse is on the same family plan. The Medicare spouse just is not adding to it.
Spousal HSA dynamics get complicated quickly. If both spouses have HSAs, or if you are trying to figure out which spouse should be the account holder, this is one of those situations where 30 minutes with someone who knows the rules saves a lot of grief.
The Medicare Side of the Decision
So far this has been about HSAs and IRS penalties. Let me close with the Medicare side, because the right HSA strategy depends partly on when it makes sense to enroll in Medicare.
If you have a large employer plan with 20 or more employees, you generally can delay Part B without a penalty until you retire. That delay is what makes the HSA contribution strategy possible. Without that delay, you would be forced into Medicare at 65 and lose HSA eligibility.
If you have a small employer plan with fewer than 20 employees, Medicare becomes primary at 65 whether you enroll or not. In that situation, you should enroll in Medicare at 65, and you cannot keep contributing to an HSA. Continuing to contribute in this scenario creates serious risk.
If you are self-employed or on a marketplace plan, those are not creditable coverage for delaying Medicare. You should enroll at 65 and accept that HSA contributions end.
A broker, in coordination with your tax advisor, can map out exactly how this should work for your specific situation. The tax advisor handles the IRS side. The broker handles the Medicare timing side. The two pieces have to fit together cleanly.
Need Help Coordinating Your HSA and Medicare Timing?
If you are approaching 65 and have an HSA, or you are already past 65 and worried you may have a backdating problem, I can help. I work with seniors and pre-retirees in Mesa, Gilbert, Chandler, Tempe, Scottsdale, and across the East Valley.
Call me at 480-296-5804 or request a free consultation. No pressure, no obligation, and no cost to you. I am not a tax advisor and cannot file your taxes, but I can walk you through the Medicare timing piece and connect you with a qualified CPA if your situation needs more involved tax work.