The 8-Month Part B Special Enrollment Period

When active employer coverage ends, an 8-month clock starts for Part B enrollment without penalty. The clock is tied to employment ending — not to when COBRA runs out.

The Part B Special Enrollment Period gives you 8 months to enroll in Part B without a late enrollment penalty after you lose active employer group coverage. The 8 months generally start the month after employment ends or the month after the qualifying employer coverage ends, whichever comes first. COBRA does not extend this window. Retiree coverage does not extend this window. If you wait until COBRA runs out 18 months later to enroll in Part B, your SEP has long since closed, and you will likely pay a Part B late enrollment penalty for the rest of your life. The clock is the clock. Mark the date.

This is the timing rule most often misunderstood — and the misunderstanding is permanent. The clock starts when employment ends, not when bridge coverage ends.

The short answer

When active employment or the qualifying employer group coverage ends, you have an 8-month Special Enrollment Period (SEP) to enroll in Part B without a late enrollment penalty. (Medicare.gov — Working Past 65)

The 8 months generally start the month after employment ends or the qualifying coverage ends, whichever comes first.

• COBRA does not extend the SEP. Even though COBRA can continue your employer plan for 18 months (or longer in some cases), those months do not extend your Part B window.
• Retiree coverage does not extend the SEP. Retiree coverage is valuable, but for Part B SEP purposes, it is not active employer coverage.
• If you miss the 8-month window, you generally have to wait for the General Enrollment Period (January 1 to March 31 each year) — and you will likely face a Part B late enrollment penalty.

How this applies to you

If you are leaving active employment at or after 65: Mark the date your employment ends. That date starts the 8-month clock for Part B. See Leaving Work Coverage? Medicare Decisions Can Change Quickly for the broader picture.

If you are on COBRA: Your Part B SEP may have already started — or may already have ended. Verify the date your active employer coverage ended (usually the same date as your employment, not when COBRA started). See COBRA and Medicare: Why the Timing Is Different.

If you are on retiree coverage: Your Part B SEP started when your active employment ended. If that was more than 8 months ago and you did not enroll in Part B, you may need the General Enrollment Period. See The General Enrollment Period: What It Fixes and What It Does Not.

If you are still working but planning to leave: Plan for the SEP before the last day of work. Know the date the coverage ends. Decide whether to enroll in Part B during the SEP or coordinate with new coverage.

What starts the 8 months

The SEP generally starts the earlier of:

1. The month after employment ends, or
2. The month after the qualifying employer group coverage ends.

If both happen on the same date (which is common), they start the clock together. If the coverage ends first (for example, the employer drops coverage but employment continues), the coverage end date may start the clock.

Verify the exact start date with Social Security before relying on a particular interpretation.

What does not start or extend the 8 months

• The day COBRA starts. COBRA is a continuation of employer coverage after employment ends. The SEP clock generally started when active employment ended, not when COBRA began.
• The day COBRA ends. Even if COBRA continues for 18 months, the Part B SEP does not.
• The day retiree coverage starts. Retiree coverage typically begins after active employment ends. The SEP clock has already started.
• The day you start collecting a pension. Pensions are not Medicare-qualifying coverage events.
• Loss of dental, vision, or other supplemental benefits. Only the loss of qualifying group health coverage from current employment triggers a Part B SEP.

What happens if you miss the SEP

If you miss the 8-month window:

• You may have to wait for the General Enrollment Period (January 1 to March 31 each year) to enroll in Part B. Coverage from a GEP enrollment generally starts the first of the month after enrollment under current rules — verify the current start-date rule with Social Security. (Medicare.gov — When Can I Sign Up)
• You will likely face a Part B late enrollment penalty — 10% of the Part B premium for each full 12-month period you could have had Part B but did not — and you pay that penalty for as long as you have Part B. (Medicare.gov — Part B Late Enrollment Penalty)
• If you have gone without Part B and also without creditable Part D coverage, a separate Part D late enrollment penalty may apply.

The General Enrollment Period is a real safety net, but it is a safety net — not a reset. See The General Enrollment Period: What It Fixes and What It Does Not.

What to check right now

1. What was the last day of active employment? Get the exact date from your employer’s HR or benefits team in writing.
2. What was the last day of active employer group coverage? This may be the same day as employment, or it may be the last day of the month, or it may be later. Get the exact date.
3. Did the employer offer COBRA, and did you elect it? If yes, write down both the date COBRA started and the date your active employer coverage ended.
4. What does Social Security show as your Part B eligibility date? Confirm with Social Security.
5. Has your 8-month window started? Is it still open? Do the math. Eight calendar months from the month after active coverage ended.

A simple timing prompt

”Did my active employer coverage end? And how many months ago?”

If active coverage ended more than 8 months ago and you do not have Part B, contact Social Security promptly. The window has likely closed, and the General Enrollment Period may be your next opportunity.

What people often get wrong

• ”COBRA gives me an extra 18 months for Part B.” It does not. The Part B SEP clock is tied to active employment ending, not COBRA ending.
• ”I have until 8 months after I retire.” Closer, but verify whether the active coverage and the active employment ended on the same date. They usually do; sometimes they do not.
• ”My HR said I am fine.” HR teams handle many issues. Medicare timing is not always their specialty. Confirm with Social Security in writing.
• ”I can just sign up next year.” Next year is the General Enrollment Period — and likely a penalty.

The 8 months are real, but the clock is shorter than people think. Mark the date. Verify with Social Security. Move while the window is open.

This is a piece of a bigger picture

This article is part of Enrollment & Timing.