Medicare’s Annual Enrollment Period runs October 15 through December 7 every year, according to Medicare.gov, and for California employers with workers approaching 65, that window lands at the worst possible time — in the middle of most companies’ own open enrollment season. ServicePro Insurance Solutions, a group health and employee benefits brokerage in San Diego and Carlsbad, works with employers across California and nationwide on exactly this overlap: making sense of Medicare open enrollment employer group coverage rules well enough to answer basic employee questions, without crossing into individual Medicare advice brokers aren’t licensed to give.

The 20-Employee Rule: Who Pays First

The most important number in this conversation is 20. Under federal Medicare Secondary Payer rules, if an employer has 20 or more employees on the payroll for at least 20 calendar weeks in the current or prior year, the group health plan pays primary for any actively working employee 65 or older, and Medicare pays secondary. Below that threshold, the roles flip: Medicare pays primary, per the Centers for Medicare & Medicaid Services.

A 12-employee accounting firm and a 45-employee logistics company need different conversations with employees turning 65, simply because the plan that pays first is different.

When Employees Can Delay Medicare Part B Without a Penalty

Employees often assume they must enroll in Medicare the moment they turn 65 or face a permanent penalty. Not true if they have active group coverage. An employee working past 65 and covered through current employment — their own or a spouse’s — qualifies for an 8-month Special Enrollment Period to sign up for Part B once that coverage ends, according to Medicare.gov. That protection applies at employers of any size.

COBRA and retiree coverage don’t count — only active employment does. An employee who retires or drops to part-time status starts that 8-month clock immediately, whether they realize it or not.

Medicare Open Enrollment Dates and Why the Timing Overlaps

Medicare’s Annual Enrollment Period — October 15 through December 7 — is when current Medicare beneficiaries switch Medicare Advantage or Part D drug plans for the following year. It has nothing to do with an employer’s own open enrollment period, but the two land within weeks of each other every fall, which is why HR starts fielding Medicare questions right when it’s least prepared to answer them.

An employee turning 65 in October or November is often sorting two decisions at once: stay on the group plan, or do something about Medicare. Getting ahead of the Medicare open enrollment employer group coverage overlap is mostly about anticipating the calendar, not solving a legal problem.

What Employers Should Tell Employees Turning 65 (and What They Shouldn’t)

Here’s the compliance line that matters: an employer or broker can explain how the group plan works and what the law says about size thresholds and timing. What they cannot do is tell a specific employee whether they, personally, should keep the group plan, switch to Medicare, or add a Medicare Supplement plan — that’s individual advice, and it belongs with a licensed Medicare agent or SHIP counselor, not HR.

A practical script for HR: confirm whether the company is above or below 20 employees, explain in general terms which plan would pay first, and point the employee to a Medicare specialist for the actual decision. This comes up constantly in the employees turning 65 group health plan conversation, because the right choice depends on employer size, plan cost, and the employee’s own health.

Coordinating Benefits Communications During This Window

Employers who handle this best build a short, standard communication into their open enrollment packet every year — not a one-off email when someone turns 65. A one-page insert covering the 20-employee rule, the 8-month Part B window, and who to contact for individual guidance heads off most confusion before it starts, especially for employees comparing the cost of staying on a group medical plan against Medicare.

Medicare questions aren’t the only benefit that gets rushed this time of year — our post on why employers shouldn’t overlook disability insurance during open enrollment covers a similar blind spot. If your materials don’t address the Medicare overlap yet, Request a Quote and we’ll help build that language into your renewal packet.

Common Mistakes That Create Risk for Employers

A few patterns show up repeatedly. Employers under 20 employees sometimes tell a new 65-year-old hire the group plan will always pay first, when Medicare actually pays primary at that size, leaving unexpected coverage gaps. Employers over 20 sometimes let an employee assume they must drop the group plan at 65, when it’s actually the correct primary payer.

• Not re-checking headcount when a company crosses the 20-employee threshold mid-year
• Letting a manager, rather than HR or a broker, answer Medicare questions informally
• Failing to document that only general, neutral information was provided

Each is fixable with a standard process. The goal is consistency — every employee turning 65 gets the same general information, delivered the same way.

How ServicePro Insurance Solutions Helps HR Manage These Conversations

ServicePro Insurance Solutions works with 50+ carriers and doesn’t charge employers a fee — compensation comes from the carriers, same as any licensed broker. We help HR build the headcount tracking and referral process that keeps these conversations compliant, while pointing employees who need individual Medicare vs employer health insurance California guidance to the right licensed resource.

We also help employers evaluate whether their current group health insurance plan design still makes sense once a meaningful share of the workforce is over 65. Our renewal process builds this review into every plan year, and our overview of 2026 group health insurance market trends covers how an aging workforce factors into plan strategy.

Frequently Asked Questions

How does the 20-employee rule get counted — full-time only, or everyone?

Both full-time and part-time employees count, as long as they’re on the payroll for at least 20 calendar weeks in the current or prior year. Once an employer crosses that line, the group plan generally stays primary through the rest of that year and all of the next, even if headcount later dips.

Can an employee just stay on a small employer’s group plan and skip Medicare at 65?

They can, but it’s usually not the better financial move under 20 employees, since Medicare would already be paying primary. That’s exactly the kind of individual decision that belongs with a licensed Medicare agent, not a blanket HR answer.

How do we get help sorting out Medicare open enrollment employer group coverage questions before enrollment season?

Contact ServicePro Insurance Solutions. We’ll review your headcount, your group plan, and your open enrollment materials, then help you build language that answers common employee questions without straying into individual advice.

Sources

• Medicare.gov — Medicare Open Enrollment (October 15 – December 7)
• Centers for Medicare & Medicaid Services — Small Employer Exception to Medicare Secondary Payer Rules
• Medicare.gov — When Does Medicare Coverage Start (Special Enrollment Periods)