Your 8-month window

If you delayed Part B because you or your spouse were still working and had job-based coverage, you get a Special Enrollment Period to sign up later. Medicare.gov says it lasts 8 months after the employment or the group health plan coverage ends, whichever happens first.

Your Part B sign-up window after retiring

  1. Day 0Your job or your employer coverage ends, whichever comes first
  2. 8 monthsPart B Special Enrollment Period. Sign up any time in this window without a penalty
  3. After the windowLate penalty risk. You may have to wait for the General Enrollment Period, January 1 to March 31, and pay more for as long as you have Part B

The clock starts with whichever ends first. If you stop working but your employer keeps your coverage for a few more months, the window still starts when your job ends.

COBRA and retiree coverage don't extend it

This is the mistake that catches the most people. Medicare.gov says COBRA isn't considered group health plan coverage, so having COBRA doesn't change when your window ends. The same is true of retiree coverage.

Medicare.gov also lists the end of COBRA or retiree coverage as a situation that doesn't qualify for a Special Enrollment Period. If you wait for COBRA to run out, you may already be past your window.

Timing your Part B start

Part B generally starts the first month after you sign up. If you sign up while you or your spouse are still working, or within the first full month after employer coverage ends, Medicare.gov says you can ask to delay your Part B start date by up to 3 months.

The cleanest plan is to sign up a month or two before your retirement date and ask for Part B to start the day after your job coverage ends. That avoids both a gap and paying for Part B while you still have employer coverage.

If you already have Part A, you sign up for Part B through Social Security at SSA.gov. Social Security may ask for proof of your employer coverage, so ask your employer for it before you retire.

What the penalty costs

If you miss the window, your Part B premium goes up 10% for each full 12-month period you could have had Part B but didn't. Medicare.gov says the penalty is usually charged for as long as you have Part B, which for most people is life.

The penalty is added to the standard premium, which is $209.50 (projected by the Medicare Trustees; CMS confirms the final figure in November) a month in 2027. See how much Medicare Part B costs.

Your other deadlines when you retire

  • Medigap: your Medigap Open Enrollment Period, which lasts 6 months, starts the first month you have Part B and are 65 or older. It happens once, so start Part B when you're ready to buy Medigap.
  • Medicare Advantage or Part D: you can usually join when you first get Part B. Part D has its own late penalty if you go without creditable drug coverage.
  • Spouses: if your spouse was on your employer plan, check their Medicare and coverage dates too.

See how a Medicare Special Enrollment Period works, how Medicare works with employer or COBRA coverage, and Medicare Parts A, B, C and D explained.

Quick questions

How long do I have to sign up for Part B after I retire?

8 months after your job or employer coverage ends, whichever comes first.

Does COBRA give me more time to sign up for Part B?

No. COBRA isn't considered group health plan coverage, so it doesn't change when your window ends.

Can I sign up before I retire?

Yes. You can sign up while still working and ask to delay your Part B start by up to 3 months.

How The Jordan Insurance Agency helps

The Jordan Insurance Agency is an independent agency based in Charlotte, North Carolina. We help you pick a Part B start date that avoids a gap, and we compare Medigap, Medicare Advantage and Part D plans for your doctors and prescriptions.

There is no fee for our help. Carriers pay the agent, so your premium is the same whether you enroll with us or on your own.

Next steps: read how a Medicare Special Enrollment Period works and Medicare Parts A, B, C and D explained.

Part B sign-up rules checked October 17, 2026. Sources: Medicare.gov — When does Medicare coverage start?, Medicare.gov — Avoid late enrollment penalties, AMAC — Medicare costs 2027 (cites 2026 Medicare Trustees Report).