Usually, you have 8 months to sign up for Medicare Part B after your employment ends or your active employer health coverage ends, whichever happens first.
That is the main Medicare Special Enrollment Period people use when they retire after 65. It does not wait for COBRA to end. It does not usually wait for retiree coverage to end. And if you miss it, you can end up with a late enrollment penalty and a coverage gap.
That is the short answer. Here is how the rule actually works.
How Long Is the Medicare Special Enrollment Period After Retirement?
For Medicare Part B, the Special Enrollment Period is 8 months.
Medicare says this window starts the month after your employment ends or the month after your group health plan coverage ends, whichever happens first. If your job ends in June 2026 and your employer coverage also ends in June 2026, your 8-month clock starts in July 2026.
This rule generally applies when you delayed Part B because you had coverage from your own current job or your spouse’s current job.
If you want the official Medicare explanation, start here:
What Counts as “Retiring” for Medicare Timing?
For Medicare, the key issue is not whether you call yourself retired. The key issue is:
- when your active employment ends
- when your active employer group health coverage ends
Medicare uses the earlier of those two dates to start the Special Enrollment Period.
That is why some people get tripped up. They stop working, but their employer coverage runs through the end of the month. Or they leave work and elect COBRA, assuming that keeps the Medicare clock from starting. It does not.
If you are still sorting out whether you were even allowed to delay Part B in the first place, read Do You Need Medicare at 65 If You’re Still Working? Missouri Rules and Can You Stay on Your Spouse’s Health Insurance Instead of Medicare at 65?.
Does COBRA Extend the Medicare Enrollment Deadline?
No.
Medicare is very clear on this point: COBRA is not considered group health plan coverage for this Special Enrollment Period rule.
That means if you retire at 67, choose COBRA for 18 months, and wait until COBRA ends to apply for Medicare Part B, you may already be too late.
This is one of the most expensive mistakes I see because it feels logical from the retiree’s side. You still have insurance, so you assume you are protected. Medicare does not look at it that way.
If this is your situation, read Medicare and COBRA: The Expensive Mistake Thousands of Retirees Make.
What About Retiree Coverage?
Retiree coverage can be useful, but it usually does not protect you the way active employer coverage does.
If you are relying on a retiree plan after employment ends, do not assume you can wait to enroll in Medicare. In many cases, retiree coverage expects Medicare to be in place.
The safe question to ask is not, “Do I still have insurance?”
The safe question is, “Is this still active employer coverage based on current employment for Medicare purposes?”
If the answer is no, you should slow down and verify your Medicare timing before you miss the Part B window.
What If You Also Need Drug Coverage?
This is where people mix two different deadlines together.
The Part B Special Enrollment Period is 8 months.
But Medicare says if you leave employer or union coverage and need to join a Medicare drug plan (Part D) or a Medicare Advantage plan, your plan enrollment window is generally 2 full months after the month your coverage ends.
That shorter Part D and Medicare Advantage timeline matters. Someone can still be inside the 8-month Part B window and still miss the cleaner handoff for drug coverage.
Official Medicare pages:
If prescriptions are a major issue for you, these related guides will help:
- What Does Medicare Part D Cover?
- What Is a Medicare Part D Formulary?
- How to Compare Medicare Part D Plans in the Kansas City Area
What Forms Do You Need to Sign Up After Retirement?
In most standard after-65 retirement situations, Medicare points people to two forms for Part B enrollment:
- CMS-40B for the Part B application
- CMS-L564 for proof of employer coverage or recent employment-based coverage
Medicare lists both forms on its enrollment forms page and explains that CMS-L564 is used when you are still working, retired within the last 8 months, or lost job-based health coverage within the last 8 months.
Official source:
In plain English: do not wait until the last second to gather employer paperwork. HR delays are common.
Can You Pick Your Part B Start Date?
Sometimes, yes.
Medicare says that if you sign up for Part B while you are still working or within the first full month after employer coverage ends, you can usually request a delayed Part B start date for up to 3 months.
That can help if you are trying to line Medicare up with the exact month your employer plan ends.
This is useful when someone in the Kansas City area is retiring mid-month, using employer coverage through the end of the month, and wants Medicare to begin cleanly without paying for overlapping coverage longer than necessary.
What Happens If You Miss the 8-Month Window?
Two problems can happen.
First, you may have to wait for another Medicare enrollment opportunity instead of starting coverage when you want it.
Second, you may owe the Part B late enrollment penalty, which is usually 10% for each full 12-month period you could have had Part B but did not sign up.
If you are trying to understand the penalty side in more detail, read What Happens If You Do Not Sign Up for Medicare at 65?.
The Employer Size Question Still Matters
This article assumes you had the kind of employer coverage that let you delay Part B safely.
That is not automatic.
CMS says that for people 65 or older with group health plan coverage based on current employment, employer size affects whether the employer plan pays first or Medicare pays first. For many working-age Medicare decisions, the critical line is 20 or more employees.
Official CMS pages:
If your coverage was through a small employer, the real issue may not be “How long do I have after retirement?” The real issue may be whether you should have enrolled in Medicare earlier.
What I Tell Kansas City Retirees to Do Before Their Last Day of Work
If you are in Blue Springs, Lee’s Summit, Independence, Overland Park, or elsewhere in the Kansas City metro, I would not wait until after retirement to figure this out.
Do these five things before your last day:
- Confirm the exact date your active employer coverage ends.
- Ask HR how they handle Medicare proof-of-coverage paperwork.
- Decide whether you want Original Medicare with a Supplement or a Medicare Advantage plan.
- Build your medication list and pharmacy list if you need Part D.
- Check whether HSA contributions need to stop before Medicare starts.
That last point matters more than people expect. If HSA contributions are part of your retirement strategy, read Medicare and HSA Contributions After 65 before you enroll in any part of Medicare.
If you are still deciding between coverage styles after retirement, these are the two comparisons most people need:
- How Much Does a Medicare Supplement (Medigap) Plan Cost in 2026?
- Medicare Advantage vs Medigap in the Kansas City Area: Which Is Right for You?
A Simple Example
Say you retire on August 31, 2026 and your employer coverage also ends on August 31, 2026.
Your Medicare Part B Special Enrollment Period generally starts in September 2026 and runs for 8 months.
But if you need to pick up a Medicare drug plan or a Medicare Advantage plan because employer coverage ended, Medicare’s plan Special Enrollment Period is generally only 2 full months after August.
That is why I tell people not to think in broad terms like “I have a while.” Medicare has more than one clock running.
Frequently Asked Questions
How long do you have to enroll in Medicare after retirement?
Usually 8 months to enroll in Medicare Part B after employment ends or active employer group health coverage ends, whichever happens first.
Does COBRA count toward the 8-month Medicare Special Enrollment Period?
No. Medicare says COBRA is not considered group health plan coverage for this rule, so COBRA does not extend the Part B Special Enrollment Period.
Is the Medicare drug plan deadline also 8 months?
No. The Part B window is usually 8 months, but the Medicare Advantage and Part D enrollment window after losing employer or union coverage is generally 2 full months after the month coverage ends.
What forms do I need to sign up for Medicare after I retire?
In a standard Part B Special Enrollment Period, Medicare commonly points people to form CMS-40B for Part B enrollment and CMS-L564 for proof of employer coverage.
What if my spouse’s employer coverage is ending instead of mine?
You may still have the same type of Special Enrollment Period if you delayed Medicare because you were covered under your spouse’s current employer plan. The timing rule is still tied to when that employment or active coverage ends.
Should I wait until after I retire to start the Medicare process?
Usually no. It is safer to confirm dates, forms, and plan choices before your last day of work so you do not create a gap or miss the cleaner enrollment window for Part D or Medicare Advantage.