Americans who stay on the job past 65 and keep their employer health plan face a decision that can permanently raise their Medicare costs or save them from years of surcharges. Federal rules allow workers with group coverage through current employment to skip Part B enrollment at 65 and sign up later through a Special Enrollment Period without paying the late penalty, a 10% premium increase for each full 12-month period of delay. The catch: one misstep on timing, employer size, or coverage type can lock in that surcharge for life.
Why the Part B delay rule carries real financial weight in 2026
The penalty math is straightforward and unforgiving. Under 42 U.S.C. Section 1395r, anyone who could have enrolled in Part B but did not gets a permanent 10% premium increase for each full 12-month period they went without coverage outside a qualifying window. A worker who delays three years past initial eligibility without a valid reason would pay 30% more for Part B premiums every month for the rest of their enrollment.
That penalty disappears, however, for people who delayed Part B because they had group health plan coverage based on current employment. Once that job or coverage ends, they receive an eight-month Special Enrollment Period to add Part B without any surcharge. The protection hinges on the coverage being tied to active work, not retirement or continuation benefits.
The employer’s size determines whether these protections apply at all. Under federal Medicare Secondary Payer rules in 42 U.S.C. Section 1395y(b), the employer must have 20 or more employees for the “working aged” provisions to kick in. The regulatory definition, found in 42 CFR Section 411.170, counts an employer as meeting that threshold if it employs 20 or more people on each working day during each of 20 or more calendar weeks in the current or preceding calendar year. Workers at smaller firms do not get the same delay protection and risk the late penalty if they skip Part B at 65.
COBRA coverage and the eight-month enrollment window
One of the most consequential distinctions in the enrollment rules separates active employer coverage from COBRA continuation coverage. CMS guidance directed at employers and unions states explicitly that COBRA does not qualify for the same delay protection as an active group health plan. A worker who retires at 65, elects COBRA, and assumes they can wait to enroll in Part B could face the full late penalty when they finally sign up.
The eight-month SEP clock starts when either the job ends or the group health plan coverage ends, whichever comes first. The Social Security Administration’s enrollment instructions confirm that if someone has been covered by an active employer group health plan since turning 65 and that coverage ended within the last eight months, they can enroll in Part B without penalty. Missing that window pushes the next opportunity to the General Enrollment Period, which runs January through March each year, with coverage not starting until July, leaving a potential gap in both coverage and protection from late penalties.
COBRA complicates this timing. Because COBRA is not considered coverage based on current employment, remaining on COBRA after the job ends does not extend the eight-month SEP. A retiree who works until 67, leaves the job, and elects 18 months of COBRA might assume they can wait until COBRA ends to enroll in Part B. In reality, their penalty-free window still expires eight months after the employment or active-plan coverage ends. Enrolling after that date can trigger the lifetime surcharge tied to the number of full 12‑month periods they waited.
How to time enrollment when working past 65
Workers who plan to stay employed past 65 should start by confirming whether their employer coverage is primary or secondary to Medicare. For employers with at least 20 employees, the group plan is generally primary for active workers and their spouses who are 65 or older, and delaying Part B can make sense if the coverage is robust. At smaller firms, Medicare usually becomes primary at 65, and failing to enroll in Part B can leave workers exposed to unpaid claims and future penalties.
Understanding the basic structure of Original Medicare is essential before making this choice. Part A typically covers inpatient hospital care and is often premium-free for people with a sufficient work history, while Part B covers outpatient services and carries a monthly premium that can be increased by late-enrollment penalties or higher-income surcharges. Because Part B is where the penalty applies, decisions about delaying coverage almost always focus on this component.
Workers who decide to delay Part B should document their group health coverage and keep records from their employer plan administrator. When they are ready to enroll, the Social Security Administration requires proof of creditable coverage tied to current employment to approve a Special Enrollment Period. The agency’s instructions for signing up for Part B explain how to submit the employer verification form and the timing rules that govern when coverage begins.
Those who are unsure about their employer’s size, the status of their coverage, or the timing of retirement should seek written confirmation from their benefits office before turning 65. Clarifying whether coverage is based on active work, whether the employer meets the 20‑employee threshold, and how COBRA would interact with Medicare can prevent costly misunderstandings. Because the late-enrollment penalty is generally permanent once assessed, getting these details right the first time is far more effective than trying to fix a mistake years later.
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