Retirement & Tax Planning Answers
Should You Enroll in Medicare If You're Still Working at 65?
Quick answer
Whether to enroll in Medicare while still working depends almost entirely on your employer's size, not your age or how many more years you plan to work. If the employer has 20 or more employees, the group health plan stays primary and you can generally delay Medicare Part B without penalty as long as you're actively working and covered. If the employer has fewer than 20 employees, Medicare typically becomes primary at 65 regardless of employment status, and delaying enrollment can leave real coverage gaps. Part A is usually worth adding either way, since it's premium-free for most people, unless you're contributing to a Health Savings Account, in which case enrolling in any part of Medicare stops HSA contributions.
Employer Size, Not Age or Job Status, Decides Whether You Can Wait
Medicare's rules for people still working at 65 hinge on one fact: how many employees does the company have. If it's 20 or more, the employer plan is considered primary and Medicare would be secondary if you enrolled. That's what allows you to keep the work plan and delay Medicare Part B with no late penalty, because active employer coverage counts as creditable coverage. If it's fewer than 20, Medicare becomes primary automatically at 65, whether you're working or not. In that situation the employer plan may pay very little on claims once it assumes Medicare should have paid first, so most people in a small-group plan need to enroll at 65 rather than wait. Confirm the exact employee count and the primary/secondary designation with HR or the benefits administrator directly. Don't estimate based on how the company feels in size.
Part A and Part B are separate decisions and don't have to move together. Part A covers hospital care and is premium-free for most people who've worked and paid Medicare taxes for at least 10 years. Because there's no premium, most people in the 20-or-more-employee situation still enroll in Part A at 65 even while working, since it can pick up costs the employer plan doesn't and there's no added cost to carrying it.
Part B carries a monthly premium, which is why people with qualifying employer coverage typically wait on it until they actually retire, to avoid paying for coverage that duplicates the work plan. Once he retires, Part B needs to start right away since there's no employer coverage to fall back on.
There is one common exception to the 'add Part A now, it's free' advice: Health Savings Accounts. Enrolling in any part of Medicare, including just Part A, stops HSA contributions entirely, his and any employer match. Medicare enrollment can be retroactive up to six months (though never before age 65), which can create an unexpected conflict if he's still funding an HSA. If HSA contributions matter to him for a few more years, that needs to be worked through before enrolling in anything, even Part A alone.
COBRA and retiree health plans do not count as creditable coverage for delaying Medicare. This is one of the most common points of confusion. The rules that let someone delay enrollment apply to active employer group coverage, not to what comes after employment ends.
The HSA Contribution Rule Most People Don't Know About
When you do retire, you'll get a Special Enrollment Period: 8 months starting the month after employment ends or the group coverage ends, whichever comes first. You don't have to wait for the general enrollment period to sign up. Miss that 8-month window and you could be stuck waiting for the next general enrollment period, which runs January through March with coverage starting the first day of the month after you sign up, plus a Part B late enrollment penalty that's added to the premium permanently, for as long as you have Medicare.
Because COBRA doesn't count as creditable coverage, the SEP clock starts when active employment or the active group plan ends, not whenever COBRA runs out later. Planning the Part B start date around your actual last day of work, and confirming that date with HR, avoids both the gap and the penalty.
Three Mistakes That Turn a Simple Delay Into a Permanent Penalty
- Assuming any coverage after retirement, including COBRA or a retiree health plan, keeps the Medicare delay valid. It doesn't. Only active employer group coverage does, and the 8-month enrollment clock starts the day that coverage ends.
- Not confirming the employer's actual headcount and primary/secondary designation before deciding to delay. Guessing wrong on this point is what leads to unpaid claims or an unnecessary enrollment.
- Enrolling in Part A without checking HSA contributions first. The 6-month retroactive enrollment window can end HSA eligibility for months you didn't expect, since Part A enrollment cannot be undone once accepted.