Workers who turn 65 while covered by an employer group health plan and then leave that job face a strict, time-limited window to enroll in Medicare Part B without permanent financial penalties. Federal rules give them 8 months to act. Miss that deadline, and the late-enrollment surcharge compounds for life, raising monthly Part B premiums by 10 percent for every full 12-month period of delayed enrollment.
Why the 8-month Part B window matters right now
The stakes are straightforward: anyone who delayed Part B because a job provided group health coverage gets a single shot at penalty-free enrollment once that coverage or employment ends. According to Medicare enrollment guidance, people who postponed Part B while covered by a group health plan based on current employment can enroll during an 8-month Special Enrollment Period. The clock starts the month employment ends or the group plan coverage ends, whichever comes first.
Social Security Administration materials on when to sign up confirm that enrollees who act within this 8-month period face no late-enrollment penalties. That distinction separates workers who transition smoothly into Medicare from those who discover months later that they owe a permanent surcharge on every future Part B premium payment.
Because the penalty is tied to how long someone went without Part B after first becoming eligible, even a relatively short delay can have long-term consequences. Someone who waits three full years beyond the Special Enrollment Period could see their standard Part B premium increased by 30 percent for as long as they have Medicare. For retirees on fixed incomes, that higher monthly cost can be difficult to absorb.
COBRA does not reset the Part B enrollment clock
One of the most common and costly mistakes involves COBRA continuation coverage. Workers who elect COBRA after leaving a job often assume they can wait until that temporary coverage expires before signing up for Part B. They cannot. COBRA coverage does not extend the 8-month Special Enrollment Period under federal Medicare rules. The window applies whether or not an individual elects COBRA, and it is tied to the end of active employment or employer coverage, not the end of COBRA itself.
Consider a worker who leaves a job in January 2026 and takes 18 months of COBRA. That person still has only until September 2026 to enroll in Part B without penalty, even though COBRA might last until mid-2027. If they wait until COBRA ends, they could face both a gap in coverage and a higher premium for the rest of their time on Medicare.
The practical result: COBRA can fill a short gap, but it does not buy extra time to decide on Part B. Anyone relying on COBRA as a bridge needs to enroll in Medicare well before that 8-month window closes. Failing to do so can leave people paying for COBRA while simultaneously owing Part B late-enrollment penalties once they finally sign up.
How CMS verifies employer coverage through Form CMS-L564
Enrolling during the Special Enrollment Period requires proof. Form CMS-L564, the official request for employment information, is the standard document beneficiaries submit to show they had group health plan coverage based on current employment. The form requires an employer representative to certify the dates of both employment and health coverage. Without it, a Part B application filed during the Special Enrollment Period can stall or be denied.
In practice, that means workers approaching retirement need to coordinate with their human resources department or benefits administrator before or soon after leaving a job. Employers must confirm whether coverage was based on current employment and indicate when that coverage ended. If the employer has merged, closed, or outsourced benefits administration, tracking down a signature can take time, which eats into the 8-month window.
No publicly available CMS data shows how many applications are delayed or rejected due to incomplete CMS-L564 submissions. That gap matters because workers who receive direct notices referencing the form and its requirements are likely better prepared than those who rely solely on general web guidance. Whether targeted outreach from CMS or SSA that highlights the need for employer verification leads to higher timely enrollment rates is an open question, but the structure of the rules makes clear that documentation is not optional.
For individuals, the safest approach is to treat the end of employment as the starting gun for Medicare decisions. Confirm the exact date employer coverage will end, request completion of Form CMS-L564 as early as possible, and file the Part B application well before the Special Enrollment Period expires. That combination of timing and documentation is what protects retirees from avoidable penalties and coverage gaps as they transition from workplace insurance to Medicare.
