COBRA does not extend the Medicare Part B enrollment window tied to current employment. If you qualify, the eight-month period starts after employment or job-based coverage ends, whichever happens first. Coordinate your Medicare start date before active coverage ends: the last month to enroll is not necessarily a safe month to wait for.
If you leave a job after 65 and choose COBRA, keeping the same health plan can make the transition feel settled. Your Medicare enrollment deadline still needs a separate decision. COBRA does not extend the time to enroll in Part B, and it may pay much less than you expect if you are Medicare-eligible but not enrolled.
Count from employment or coverage ending—not from COBRA ending
For someone 65 or older who delayed Part B while covered through their own or a spouse’s current employment, SSA describes an eight-month Special Enrollment Period beginning the month after that employment or group health coverage ends, whichever happens first. You can also enroll while that qualifying employment and coverage continue.
This employment-based window applies after your Initial Enrollment Period; it does not replace that first enrollment opportunity. It also does not apply to eligibility based on end-stage renal disease. Medicare’s enrollment table explains those boundaries. Disability-based enrollment has additional family-employment rules, so check your situation individually.
A retirement example: two dates to put on the calendar
Suppose a 67-year-old already has Part A, has maintained qualifying coverage through current employment, and has not enrolled in Part B. Their job and active employee coverage both end October 31, 2026. They elect COBRA starting November 1.
| Planning question | Date in this example |
|---|---|
| When does the eight-month window run? | November 2026 through June 2027 |
| What is the final month to use that window? | June 2027 |
| When should replacement coverage be coordinated? | Before active coverage ends October 31 |
The month count is November, December, January, February, March, April, May and June. This is our application of SSA’s rule, not an individual eligibility determination. If employment ended earlier than the insurance, the earlier employment date would control.
The June deadline is not a recommendation to wait until June. SSA says Part B generally starts the first day of the month after enrollment. Medicare also permits certain start-date choices when you enroll while still working or within the first full month after employer coverage ends. Confirm your requested effective date with Social Security before ending existing coverage.
Ask what COBRA will actually pay
Ask the plan administrator: “If I am eligible for Medicare but have not enrolled, how will this plan calculate payment for my care?” Medicare warns that COBRA may cover only a small share in that situation. Also ask what happens to your COBRA coverage when Medicare begins; Medicare.gov says COBRA obtained first will probably end when you sign up.
These answers help distinguish an enrollment deadline from a usable coverage plan. Paying a COBRA premium does not, by itself, establish that postponing Medicare leaves your bills covered.
Use the Part B application route that fits
If you already have Part A, start with SSA’s Part B enrollment page. It offers an online application for people ending employer group coverage. For the fax or mail route, it identifies CMS-40B and the employment-information form CMS-L564 for this Special Enrollment Period.
Medicare’s application instructions explain that the employer completes CMS-L564. If the employer cannot do so, follow the alternative evidence instructions rather than signing the employer’s section yourself. If you need both Part A and Part B, use that page’s corresponding enrollment route instead. Railroad workers and spouses should follow its Railroad Retirement Board instructions.
If you have already waited too long
The end of COBRA does not create a new employment-based Part B window. If yours has closed, ask Social Security whether another qualifying Special Enrollment Period applies. For example, Medicare lists a separate route for certain people who missed enrollment because an employer or health plan supplied inaccurate information on or after January 1, 2023.
Without another qualifying window, the General Enrollment Period is January 1–March 31, with coverage starting the following month. A Part B late-enrollment penalty may apply; it generally adds 10% for each full 12-month period of delay that counts. Special Enrollment Period and Medicare Savings Program protections can affect the result.
Prescription coverage needs a separate check: Part D uses its own creditable-drug-coverage rules, including a gap of 63 consecutive days or more after the initial enrollment opportunity. Do not use the Part B eight-month calendar as your drug-plan deadline.
Fall plan shopping is another separate task; our Medicare Open Enrollment guide covers that distinction. For help coordinating your actual dates, find your local State Health Insurance Assistance Program (SHIP), which offers free, individual Medicare counseling. Have your employment end date, active coverage end date and COBRA notice ready.
Prepared with AI assistance using the linked Medicare and Social Security guidance, checked October 28, 2026. The retirement timeline is illustrative; no individual case review was performed.
TopicsTalk Desk Editor is the editorial byline for our coverage of U.S. Social Security, Medicare, taxes, and government benefits. Our articles are based on official government publications and include source links so readers can verify important figures, dates, and program rules. We use AI tools to assist with drafting and organizing information. Our publishing process includes checking factual claims against official sources and correcting identified errors. Learn more about our research, verification, and corrections process in our Editorial Policy.
