Still working at 65: do you need to sign up for Medicare?
The answer depends on one number: how many employees your employer has. Twenty or more, and you can keep your plan and wait. Fewer than twenty, and Medicare becomes your primary insurance on the first day of your birthday month whether you enrolled or not.
The rule, and why it exists
Medicare’s secondary-payer rules decide who pays your claims first. If you are 65 or older and covered by a group health plan through current employment at an employer with 20 or more employees, the employer plan is primary and Medicare is secondary. Because Medicare is only a back-up in that situation, the law lets you delay Part B (the part that costs $202.90 a month in 2026) without the late penalty, and gives you a Special Enrollment Period when the employment or the coverage ends.
Flip the count under 20 and the order flips too: Medicare is primary, the employer plan is secondary. If you never enrolled in Part B, the plan can pay as if Medicare had paid its share, and you owe the difference. That is the situation the phrase “you must sign up at 65” is actually about.
Two details trip people up. First, the count is employees on the payroll for 20 or more weeks in the current or prior year, not people enrolled in the plan, and it is the employer’s count, not the plan’s. Second, “current employment” is literal: COBRA, severance coverage, retiree plans, and marketplace plans do not count, even though they are health insurance and even though they may be excellent. If you are 66 on COBRA and have not enrolled in Part B, the penalty clock is already running.
What to decide in the three months before your birthday month
Part A
Premium-free if you or your spouse paid Medicare taxes for 40 quarters. Take it at 65 unless you contribute to an HSA. It pays second to your employer plan and covers hospital stays the plan may not fully cover.
Part B
Delay it if your employer has 20+ employees and you like your plan. Enroll now if the employer is under 20, or if the plan’s premium for you alone is higher than $202.90 plus a Medigap policy.
Part D
Ask HR in writing whether your drug coverage is “creditable.” If it is, you can delay Part D too. If it is not, a gap of 63 days after your Initial Enrollment Period starts the Part D penalty.
A spouse’s plan works the same way
Coverage from your spouse’s current employer counts exactly like your own, as long as the spouse is actively employed and the employer has 20 or more employees. When the spouse retires, your 8-month window starts too. Coverage through a domestic partner does not qualify; neither does a former spouse’s plan after divorce.
Two Utah situations we see often
Federal and military retirees
Hill Air Force Base civilians on FEHB can delay Part B on current employment like anyone else. Military retirees are different: at 65, TRICARE becomes TRICARE For Life and only works alongside Parts A and B. There is no still-working exception.
State, school district, and university employees
PEHP coverage from a current state or district job counts as current employment coverage. Retiree coverage after you stop working does not; enroll in Part B during the 8 months after your last day. Anyone who ever had URS or PEHP benefits can buy the PEHP Medicare Supplement at 65.
BYU and other Church-affiliated employers (DMBA)
The exception in the other direction: DMBA requires enrollment in Parts A and B at 65 plus its Deseret Alliance supplement, and the employer contribution ends at 65. There is no delay option on a DMBA plan.
Utah State University staff
USU’s retiree medical continues only until 65, then hands off to group Medicare plans. Plan Part B to start the month the university coverage ends.
What working past 65 does to the other numbers
Keep earning and your income stays high, which matters two years later: the 2026 income surcharge is set by your 2024 return, and it starts at $109,000 single or $218,000 joint. Run the surcharge calculator with the year you plan to retire in mind. And if you claim Social Security at or before 65, you are enrolled in Part A automatically, which matters if you have an HSA (see the HSA guide).
Sources
- CMS, Medicare Secondary Payer (group health plans, 20-employee threshold)
- Medicare.gov, "Avoid late enrollment penalties"
- Medicare.gov, "When does Medicare coverage start?"
- Form CMS-L564, Request for Employment Information
- TRICARE For Life eligibility (Parts A and B required)
- PEHP Medicare Supplement, "an exclusive URS benefit"
- DMBA retiree information (Medicare Parts A and B required at 65)
- CMS, "2026 Medicare Parts A & B Premiums and Deductibles" (announced November 14, 2025)
Still-working questions, answered
Do I have to sign up for Medicare at 65 if I’m still working?
Not for Part B, if your coverage comes from current employment (yours or your spouse’s) at an employer with 20 or more employees. That coverage pays first, and you get an 8-month Special Enrollment Period when the job or coverage ends. Under 20 employees, Medicare pays first and you should enroll in Parts A and B during your Initial Enrollment Period.
Should I take Part A anyway?
If you qualify for premium-free Part A and you are not contributing to an HSA, most people take it at 65: it costs nothing and pays second to the employer plan. If you contribute to an HSA, enrolling in Part A ends your eligibility and backdates up to six months.
What happens if I keep working past 65 and never enroll in Part B?
Nothing, until the job ends. Then the 8-month clock starts. Enroll in the first month so Part B begins the next month; the Medigap open enrollment window starts with Part B, and missing the 8 months triggers the lifetime penalty.
What do I need from my employer when I finally enroll?
Form CMS-L564 (Request for Employment Information), completed by the employer, proving you had coverage from current employment. Social Security uses it to waive the penalty. Ask HR early; small HR departments are slow.
Do the math
Enrollment window calculator
Your Special Enrollment Period end date from the day coverage stops.
Open the tool →
Talk it through before you decide
Bring your birth date, your work situation, and last year’s tax return. Leave knowing your enrollment window, what Medicare will cost you, and whether the income surcharge applies.
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