Short answer
A Special Enrollment Period and the CMS-L564 form are how you sign up.
Medicare.gov says if you delayed Part B because of job-based coverage, a Special Enrollment Period lets you sign up and ends 8 months after the coverage or the job ends. To prove the coverage, you have the employer complete the CMS-L564 Request for Employment Information. Medicare.gov says if the employer cannot complete it, you fill out Section B as best you can and submit other proof. Medicare.gov also describes an exceptional-conditions Special Enrollment Period when an employer or plan gave incorrect information.
Start here
What you actually came to find out
Plain answers first. Sources stay below for checking details.
How long is the window?
Medicare.gov says it ends 8 months after the coverage or job ends.
What proves my coverage?
The employer completes the CMS-L564 Request for Employment Information.
What if the employer will not fill it out?
Medicare.gov says complete Section B and submit other proof.
What if I got wrong information?
An exceptional-conditions period may apply, says Medicare.gov.
Special Enrollment
8-month window
Medicare.gov says it ends 8 months after job-based coverage or employment ends.
Source trail: Medicare.gov
The form
CMS-L564
Medicare.gov says this Request for Employment Information proves job-based coverage.
Source trail: Medicare.gov
If denied
Other proof
Medicare.gov says complete Section B and submit other proof of coverage.
Source trail: Medicare.gov
Bad information
Extra period
Medicare.gov describes an exceptional-conditions period for incorrect information.
Source trail: Medicare.gov
The real planning question is matching the paperwork to the window so coverage starts when your job-based plan ends, without a gap.
Neutral landscape
The shape of the question
Medicare.gov is the main source because it defines the Special Enrollment Period for job-based coverage and its 8-month clock.
Source trail: Medicare.gov
The proof comes next, and Medicare.gov names the CMS-L564 Request for Employment Information.
Source trail: Medicare.gov
The denial situation is answered by Medicare.gov, which says to complete Section B and send other proof when the employer cannot help.
Source trail: Medicare.gov
The misinformation case matters because Medicare.gov provides an exceptional-conditions Special Enrollment Period.
Source trail: Medicare.gov
Curator core
What the authorities say
These sources are here for the reader who wants to check the work. The plain-English answer stays above them.
Source 01
Medicare.gov
When Does Medicare Coverage Start
Medicare.gov explains the Special Enrollment Period for job-based coverage and the exceptional-conditions Special Enrollment Period for people given incorrect information.
Source framing
Medicare.gov says a Special Enrollment Period for job-based coverage ends 8 months after the coverage or employment ends, and that an exceptional-conditions period applies when an employer or plan gave incorrect information.
Strongest for: Special Enrollment Periods for Part B after working past 65
Read at Medicare.govSource 02
Medicare.gov
Medicare Enrollment Forms
Medicare.gov lists the enrollment forms, including the CMS-L564 Request for Employment Information used to prove job-based coverage.
Source framing
Medicare.gov says the CMS-L564 Request for Employment Information gives the Social Security Administration proof of job-based coverage for Part B sign-up.
Strongest for: the CMS-L564 employer-proof form for Part B
Read at Medicare.govSource 03
Medicare.gov
Ready to Sign Up for Part A and Part B
Medicare.gov explains how to submit Part B enrollment, including what to do if the employer cannot complete the CMS-L564.
Source framing
Medicare.gov says to have the employer complete the CMS-L564, and that if they cannot, you complete Section B as best you can and submit other proof of job-based coverage.
Strongest for: submitting Part B proof when the employer cannot complete the form
Read at Medicare.govPlain-English forks
The forks people face
Most retirement questions hide a few smaller decisions. These are the practical pieces that change the plan.
Is your job-based coverage still active or ending?
Why it matters: The Special Enrollment clock runs from when the coverage or job ends.
In real life: This fork sets your deadline.
What to look at: What to look at: Medicare.gov when-coverage-starts.
Can your employer complete the CMS-L564?
Why it matters: If not, Medicare.gov lets you complete Section B and send other proof.
In real life: This fork is the path when a denial is about proof.
What to look at: What to look at: the CMS-L564 form and your coverage records.
Were you given incorrect information?
Why it matters: An exceptional-conditions period can apply when a plan or employer misinformed you.
In real life: This fork can reopen a missed window.
What to look at: What to look at: the exceptional-conditions Special Enrollment Period.
Common questions
Quick answers
Short, plain answers for the questions people usually have next. The source trail stays available below.
How long do I have to sign up for Part B after my job coverage ends?+
Medicare.gov says the Special Enrollment Period ends 8 months after the job-based coverage or the employment ends, whichever comes first.
What form proves my employer coverage?+
Medicare.gov says the CMS-L564 Request for Employment Information gives Social Security proof of job-based coverage.
I was denied because my proof did not cover enough time. What now?+
Medicare.gov says have the employer complete the CMS-L564, and if they cannot, complete Section B as best you can and submit other proof of job-based coverage.
Does COBRA count as coverage based on current employment?+
Medicare.gov says COBRA is not considered coverage based on current employment for this Special Enrollment Period.
What if I was given incorrect information?+
Medicare.gov describes an exceptional-conditions Special Enrollment Period that can apply when an employer or plan gave incorrect information.
How this page is curated
This page uses Medicare.gov when-coverage-starts, the enrollment-forms page, and the ready-to-sign-up page. It separates the enrollment window from the proof form because Medicare.gov treats them as distinct steps.
Read the planner methodologyTrust anchor
Sources used on this page
Every source named above is listed here in one place.
Medicare.gov. When Does Medicare Coverage Start
https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-startMedicare.gov. Medicare Enrollment Forms
https://www.medicare.gov/basics/forms-publications-mailings/forms/enrollmentMedicare.gov. Ready to Sign Up for Part A and Part B
https://www.medicare.gov/basics/get-started-with-medicare/sign-up/ready-to-sign-up-for-part-a-part-b
Before you act on this
This plan is educational. It is not personalized financial, tax, or insurance advice. Projections illustrate the math, they do not predict the future. Talk to your own licensed financial professional before acting on any of it.