Quick answer: If you delayed Medicare Part B because you had group health coverage based on current employment (yours or a spouse’s), Medicare.gov and Social Security describe an eight-month Special Enrollment Period to sign up for Part B after that employment ends or the group coverage ends, whichever comes first. Signing up in that window is the usual official path to avoid a Part B late enrollment penalty tied to that delay. COBRA and retiree coverage generally do not count as coverage based on current employment for this Part B SEP, which is a frequent source of missed deadlines. Part D has a different clock: official materials warn that a gap of 63 days or more without creditable drug coverage can trigger a late enrollment penalty. This article focuses on the period after coverage or employment ends; coordinating Medicare while you are still working is covered in working past 65. It also belongs in our Medicare guide.
Sources: Medicare.gov “Working past 65” and enrollment publications; Social Security Administration materials on the Medicare Part B Special Enrollment Period (8-month SEP after employment or group coverage based on current employment ends, whichever is first; COBRA and retiree coverage generally do not qualify as current-employment coverage). Medicare.gov creditable coverage / Part D late enrollment (63-day) materials; CMS-40B and CMS-L564 as the official forms commonly used to document employer coverage — confirm current form numbers and filing instructions on Medicare.gov and SSA.gov. Official URL fetched 2026-11-10 for the 2026 standard Part B premium: https://www.cms.gov/newsroom/fact-sheets/2026-medicare-parts-b-premiums-deductibles and https://www.medicare.gov/basics/costs/medicare-costs Checked November 2026, with live-page confirmation the same day.. This is general consumer information, not legal, tax, medical or benefits advice. Medicare rules, plan designs and dollar amounts change. Confirm current details on Medicare.gov, with CMS, Social Security, your plan, and a State Health Insurance Assistance Program (SHIP) counselor before you rely on a figure or a deadline.
The Eight-Month Part B Window, and What Starts the Clock
Many people who work past 65 delay Part B because they still have a group plan from a current job. Official materials allow that delay, with conditions, so you are not forced to pay two medical premiums at once. The risk shows up when the job or the group coverage ends. You then have a limited official window to enroll in Part B without the late-enrollment penalty that can otherwise apply.
Medicare.gov and Social Security describe that Special Enrollment Period as eight months long. It is tied to coverage based on current employment, and official language says the period is measured after the employment ends or the group coverage ends, whichever comes first. “Whichever comes first” is easy to miss if you assume the clock starts only when the last claim is paid, or only when COBRA runs out. If you leave the job in June and the group plan formally ends later, do not assume you can wait until the later date without reading official rules and asking Social Security or SHIP.
This is not the same clock as your Initial Enrollment Period around age 65, which we cover in when to sign up for Medicare. It is also not the fall Open Enrollment Period for Advantage and drug plans, and it is not the January–March general enrollment period for people who missed earlier Part B windows. Using the wrong calendar is how people end up in a later enrollment slot with a penalty or a coverage gap.
COBRA and retiree coverage need special care. Official consumer materials have long explained that COBRA and retiree plans generally are not treated as coverage based on current employment for this Part B Special Enrollment Period. If you decline Part B because you are on COBRA or a retiree plan, you may already be outside the eight-month SEP, or the clock may have started when you (or your spouse) stopped working. Confirm that point with Social Security and a SHIP counselor before you treat COBRA as a safe reason to delay Part B. This is one of the most common expensive misunderstandings in Medicare enrollment.
If you are still working and deciding whether to add Part B now or later, use our working-past-65 guide and official Medicare.gov pages on coordination of benefits. The size of the employer group can affect whether Medicare or the group plan pays first. That “still employed” analysis is a different article; this one assumes the job or the current-employment coverage is ending or has just ended.
Part D, Paperwork and How to Enroll Without a Gap
Medical insurance (Part B) and drug coverage (Part D) have separate late-enrollment rules. Even if you enroll in Part B on time through the eight-month SEP, you can still face a Part D penalty if you go 63 days or more without creditable drug coverage, according to official Medicare.gov materials. Employer drug coverage may or may not be creditable. Ask the employer or plan administrator for a creditable coverage notice; do not guess from the fact that you had a pharmacy card.
If your employer drug coverage is ending, look at stand-alone Part D plans or Medicare Advantage plans that include drug coverage, using Medicare.gov’s official comparison tool, and use an official Part D Special Enrollment Period if you qualify because you are losing creditable coverage. The Part D SEP timing is not automatically identical to the eight-month Part B SEP. Confirm the drug-plan start date so you do not have a long gap.
Enrollment in Part B during a Special Enrollment Period is generally handled through Social Security, not only through a private plan. Official materials commonly point to Form CMS-40B (application for Part B) and Form CMS-L564 (request for employment information) so the employer can document the coverage that supports the SEP. Confirm the current form numbers, where to send them, and whether you can complete them online on SSA.gov or Medicare.gov, because filing instructions can change. Keep copies. A missing employer signature is a frequent delay.
Coverage start dates depend on when you file during the eight-month window. Official publications explain the start-month rules; do not assume coverage begins the day you leave work, and do not assume it always begins the first of the next month. Ask Social Security for the start date that applies to your filing month, and time Medigap, drug coverage, and any COBRA decision around that official date rather than around a verbal guess.
Medigap may be available when employer coverage that pays after Medicare is ending, and official guaranteed issue materials describe a window measured in days after coverage ends or after a notice or claim denial. That Medigap clock is yet another calendar, separate from the eight-month Part B SEP. If you will want a supplement, read the official guaranteed issue situation that matches your group-plan ending and apply on time.
Premiums will change when employer coverage ends. You generally will pay the Part B premium (the 2026 standard amount announced by CMS is $202.90 per month for people who pay the standard premium; IRMAA can raise it, as our IRMAA article explains). You may also pay a Part D premium and, if you buy it, a Medigap premium. This article does not invent a replacement-cost estimate for your former group plan.
If you miss the eight-month Part B SEP, official rules may push you to a later enrollment opportunity, and a late enrollment penalty may apply for as long as you have Part B. Our late enrollment penalties article covers how official penalties are described; the practical advice is not to test the window.
A Checklist When a Job or Group Plan Is Ending
As soon as you know employment or group coverage will end, write down four dates: last day of work, last day of group medical coverage, last day of creditable drug coverage if that is different, and any COBRA election deadline. Then call Social Security or use official online enrollment for Part B if you delayed it, ask the employer for the employment-verification form, and compare drug plans on Medicare.gov.
Tell a SHIP counselor the same dates. Bring the group plan’s certificates of creditable coverage if you have them, plus any notice that coverage is ending. If a spouse’s job was the source of coverage, official SEP rules can still apply, but the “current employment” facts must be the spouse’s, and you should confirm that with official sources rather than assuming every dependent situation is identical.
Do not drop employer coverage until you have a written official start date for Part B (and for Part D if you need it). People sometimes resign or decline COBRA and then discover a filing delay. Conversely, do not assume COBRA extends your Part B SEP.
If you qualify for a Medicare Savings Program or Extra Help, apply; those official programs can help with premiums or drug costs and are described on Medicare.gov and in our Extra Help guide. Losing a job can change income, which can change eligibility.
After enrollment, watch the first Medicare card, the Part B start date printed on official notices, and the first claims. If an employer plan paid a claim after it should have ended, or Medicare denied a claim because Part B had not started, call both the group plan and 1-800-MEDICARE with your dates in hand.
Job changes, reductions to part-time hours, and “you can stay on the plan through the end of the year” promises should all be verified in writing against official SEP rules. The eight-month window is generous compared with some other Medicare clocks, and it still closes.
Coordinating End Dates With COBRA, Spouses and Delayed Paperwork
HR departments and plan administrators sometimes describe COBRA as a bridge that “covers you for Medicare too.” Official Medicare rules are stricter. COBRA can be valuable medical coverage in its own right, and official Medigap materials even discuss buying a supplement right away or waiting until COBRA ends in some guaranteed issue situations. The Part B Special Enrollment Period based on current employment is still a different clock, and official consumer materials say COBRA generally does not extend that eight-month Part B window. Get the last day of current employment and the last day of group coverage in writing, then have Social Security or SHIP map those dates to Part B, Part D and Medigap separately.
Spouses and partners on the same employer plan can have different Medicare needs. One person may already have Part B; the other may have delayed it. Official SEP eligibility depends on the current-employment coverage facts, including coverage through a spouse’s job, but each person still files their own Part B enrollment when required. Do not assume a single employer letter enrolls both people.
Late or incomplete CMS-L564-style employment-verification forms are a common reason coverage starts later than expected. Follow up with the employer if the form sits in a personnel mailbox, and keep proof that you requested it. Ask Social Security what official start date applies to the month you actually file, then set drug and Medigap start dates to that answer. A resignation date, a last paycheck date, and a group-plan termination date can be three different days.
People who are offered retiree coverage after they stop working should read official guidance before they decline Part B. Retiree plans, like COBRA, generally are not current-employment coverage for the Part B SEP. Some retiree plans coordinate with Medicare only after Part B is in place, which is another reason to confirm with the plan administrator and SHIP rather than guessing.
If a layoff, disability leave, or reduction in hours changes eligibility for the group plan, ask whether official “current employment” still exists. Those facts can start a clock earlier than people expect. Write down the answer and the name of the person who gave it, then confirm with Social Security.
Budget for the official Part B premium and, if you need them, Part D and Medigap premiums starting on the official start dates. Lost employer coverage can also change eligibility for Extra Help or a Medicare Savings Program, which is worth applying for rather than waiting to see the first bills.
Frequently Asked Questions
How long is the Part B Special Enrollment Period after employer coverage?
Official Medicare.gov and Social Security materials describe an eight-month Special Enrollment Period after coverage based on current employment ends or employment ends, whichever comes first.
Does COBRA give me the same eight-month Part B window?
Generally no. Official consumer materials say COBRA and retiree coverage usually do not count as coverage based on current employment for this SEP. Confirm your situation with Social Security and SHIP before you delay Part B for COBRA.
Is the Part D deadline the same eight months?
No. Part D uses different Special Enrollment Period rules, and official materials warn about a 63-day gap without creditable drug coverage.
Where do I sign up for Part B during the SEP?
Typically through Social Security, often with official forms that document employer coverage. Confirm current instructions on SSA.gov and Medicare.gov.
What if I am still working and only thinking about leaving?
Use official working-past-65 guidance first. The eight-month clock described here starts after employment or current-employment coverage ends.
Will I owe a late enrollment penalty if I enroll during the SEP?
Signing up during the official eight-month SEP is the usual path official sources describe for avoiding a Part B late enrollment penalty tied to that delay, if you qualified to delay because of current-employment coverage. Confirm your own history with Social Security.
