Should I delay Medicare Part B if I’m working past age 65?

Maybe. If your employer has 20 or more employees and your coverage is a group health plan from current employment, delaying Part B is usually penalty-free while that coverage lasts. If the employer has fewer than 20 employees, Medicare generally becomes primary the month you turn age 65, and delaying Part B can leave a large gap.

Revised: 8/17/26
Jason Baar
Fee-Only Medicare Advisor
NPN #2033715

Start with the employer’s size

For most people working past their 65th birthday, the first question is not whether the coverage looks good. It is how many employees the employer has.

If the employer has 20 or more employees, the group health plan generally stays primary after your 65th birthday. That means the employer plan pays first. Medicare, if you enroll, pays second. In that situation, delaying Part B is usually allowed without a late penalty as long as the coverage is from current employment.

The phrase to confirm with HR is specific: “group health plan from current employment.”

Coverage through a spouse’s current employment counts the same way. If your spouse is still working and you are covered under that employer’s group health plan, the same employer-size rule applies.

The under-20 problem

If the employer has fewer than 20 employees, Medicare generally becomes primary the month you turn age 65, whether or not you signed up.

That is the trap.

The employer plan usually becomes secondary. A secondary plan expects Medicare Part B to be in place. Without Part B, the plan may pay only the roughly 20% share it owes as secondary, leaving the roughly 80% Medicare would have paid as your bill.

If the head count is not obvious, call HR. One call usually settles it.

There is one wrinkle. A multi-employer plan, where several employers are pooled into one plan, can request to stay primary even when your specific employer has fewer than 20 employees. It is rare, but real. HR should know whether that applies.

COBRA and retiree coverage do not count the same way

Two kinds of coverage cause a lot of trouble because they look like employer coverage but Medicare does not treat them that way.

COBRA is the option to keep a former employer’s health plan for a limited time after leaving the job, usually at up to 102% of the group cost. You may have the same doctors and the same card, but Medicare does not count COBRA as current-employment coverage.

Medicare says it this way: “COBRA isn’t considered group health plan coverage. Getting COBRA doesn’t change when this Special Enrollment Period ends.”

Retiree coverage has the same problem. Retiree coverage is health insurance a former employer offers after you no longer work there. It is not current-employment coverage. Delaying Part B because you have retiree coverage can let the Part B penalty build quietly.

The common issue is that the employment relationship Medicare cares about has already ended.

The 8-month Part B Special Enrollment Period

The Part B Special Enrollment Period is the window that lets you enroll in Part B after delaying it for current-employment coverage.

It starts the first day of the month after your current-employment coverage ends or the employment itself ends, whichever comes first. It ends exactly 8 months later. There is no grace period. COBRA does not pause it or stretch it.

You can enroll in Part B during that 8-month window without a late penalty. You can also enroll while you are still covered. You do not have to wait until the job or coverage ends.

Once you file, Part B coverage starts the first of the following month. If you file in month 7, coverage starts in month 8.

The classic disaster is simple. Someone leaves a job at age 66, elects 18 months of COBRA, uses all of it, and then tries to sign up for Part B at month 19. The window closed 11 months earlier, and the late penalty attaches to Part B for life.

The fix is also simple. The day employment ends, write the real end date on a calendar. Count 8 months forward. Write that date down as “Part B enrollment deadline, regardless of COBRA.”

HSA contributions need their own calendar

An HSA, or Health Savings Account, has a separate rule.

Beginning with the first month you are enrolled in Medicare, your HSA contribution limit is zero. Not reduced. Zero. In the year you enroll, the limit is prorated by month.

Premium-free Part A taken after your 65th birthday can start retroactively up to 6 months back, but never earlier than the month of your 65th birthday. HSA contributions made during those retroactive months become ineligible. The IRS can treat them as excess contributions, with a 6% penalty for each year they stay in the account.

That is why Medicare’s working-past-age-65 guidance recommends stopping HSA contributions 6 months before you retire or file for Social Security. Filing for Social Security at age 65 or later automatically files you for Parts A and B.

One timing rule is friendlier. The 6-month Medigap window opens the month you are both age 65 or older and enrolled in Part B. Medigap means Medicare Supplement insurance. If your Part B delay is legitimate, that Medigap window waits too.

For more plain-English Medicare help, visit the Free Medicare Guides library.