Switching from employer insurance to Medicare

Say you file on time and your employer's form arrives late. Your part was done; the application was not. This switch runs on two calendars, and only one of them is yours.

How does the switch work?

Moving from employer insurance to Medicare uses a Special Enrollment Period, which lets a person sign up for Part B without a late enrollment penalty. It applies to coverage held through your own job or a spouse's job, and it is available for a limited time only. The switch is a deadline.

Most people in this situation already have Part A, taken at 65 while they kept working. The switch then means adding Part B, not starting from nothing.

If you have a disability and your coverage comes through a non-spouse family member's current employment, their employer must be in a large group health plan for this to apply.

When does my window start?

The window ends 8 months after the group health plan coverage or the employment ends, whichever happens first. Two clocks exist and the earlier one governs. Call it the Two Clocks problem: the date your job ended and the date your insurance ended are frequently not the same date, and only the earlier one counts.

The Two Clocks reading comes from four words in Medicare's own sentence, "whichever happens first", which is easy to read past and expensive to misread.

A worked case. Employment ends 31 March. The employer runs the plan to 30 June as a courtesy. The count starts in March, not June. Someone marking their calendar from June has already lost three months and does not know it.

The period formally starts the first month after your Initial Enrollment Period ends, so for anyone past 65 it is running the moment the earlier clock stops.

Where do I actually sign up?

Enrollment goes through Social Security, not through Medicare, even though the program and the card both say Medicare. For someone who already has Part A and is adding Part B, Medicare directs them to SSA.gov to apply online. Completed paper forms go to a local Social Security office by fax or mail.

Online is the faster route where it is available.

Medicare.gov is where the rules are published. Social Security is the agency that accepts the application and holds the record of it.

What form does my employer fill?

Form CMS-L564 is the one your employer completes, confirming the job-based coverage you held. It travels with your Part B application. Because it depends on someone else's calendar rather than yours, it is the step to start first rather than last, and the only step whose timing you do not control.

Form CMS-L564 is the one your employer completes, confirming the job-based coverage you held.

If the employer cannot complete it, fill in Section B yourself as best you can, do not sign it, and submit proof of your job-based health insurance instead.

Two forms do two different jobs, and sending the wrong one is a common delay.

The form	What it proves	Who completes it
CMS-L564	You had job-based coverage while working	Your employer
CMS-40B	You are applying for Part B	You

If the employer cannot complete the first one, you may fill in its Section B yourself but not sign it, and send proof of the job-based insurance with it.

That fallback exists precisely because former employers go quiet, change payroll providers, or take weeks to answer. Knowing it exists before you need it is worth more than knowing it after.

Does COBRA extend my time?

COBRA does not extend the window. Medicare states that COBRA is not considered group health plan coverage for this purpose, and that taking COBRA does not change when the Special Enrollment Period ends. Retiree coverage behaves the same way. Both continue after the employment has ended, and the protection was attached to the employment.

Medicare lists COBRA coverage ending, and retiree coverage ending, among the situations that do not qualify a person for a Special Enrollment Period.

This is the single most common way the switch goes wrong. COBRA looks and feels like insurance, because it is. It simply is not the kind that holds this door open.

When does my coverage begin?

Part B coverage generally begins the first month after you sign up. One exception exists. Signing up while you or your spouse are still working, or within the first full month after coverage ends, lets you ask to delay the Part B start by up to 3 months. The delay is never automatic.

That option expires long before the eight month window does.

Missing the window entirely means waiting for the General Enrollment Period, which runs January 1 to March 31 each year, with coverage starting the month after you sign up, and possibly paying a monthly late enrollment penalty.

Two pieces of timing advice come straight from Medicare, and both are about avoiding a gap rather than avoiding a penalty.

Your coverage starts the month after Social Security, or the Railroad Retirement Board, processes your completed form. Not the month you send it.

So if your employer coverage is ending, check the date it ends and sign up about a month earlier. Medicare states this is what helps you avoid a gap in coverage.

If the coverage is changing rather than ending, the question goes to your benefits administrator. Ask what you will need, and ask specifically whether you will need to sign up for both Part A and Part B.

Four places can answer a question this article cannot, and they answer different questions.

Social Security handles Part A and Part B enrollment questions. Your State Health Insurance Assistance Program gives free one-to-one help with choosing a plan, reviewing coverage and understanding costs, and it is not connected to any insurance company.

Your group health plan or benefits administrator is the only party who can say how your own benefits will work alongside Medicare. Medicare itself is on 1-800-MEDICARE, 1-800-633-4227, with TTY on 1-877-486-2048.

The third one is the one people skip, and it is the only one holding your actual plan documents.

What this means for you

Take the earlier of your two dates, the day the job ended or the day the plan ended, and count eight months from there. Start the employer form immediately, because it runs on somebody else's calendar. Sign up at Social Security. Do not let COBRA reset the clock in your head.

For a household, the cost of the Two Clocks mistake is not a one-off. The penalty that follows a missed window is monthly, and it lasts as long as the coverage does.

FAQ

When does the eight months actually start?

It ends eight months after the group health plan coverage ends or the employment ends, whichever of the two happens first. Those two dates are often different, and people almost always plan from the later one.

If your job ends in March and the employer keeps the plan running until June, your count begins in March. Take the earlier date, always, and count from there. If you are unsure which date applies to you, ask your benefits administrator for both dates in writing rather than assuming they are the same.

It starts the first month after your Initial Enrollment Period ends (W2), and it ends 8 months after the group health plan coverage or the employment ends, whichever comes first (W3). The whichever-comes-first is the part that catches people.

Do I sign up at Medicare or at Social Security?

At Social Security. If you already have Part A and are adding Part B, Medicare directs you to SSA.gov to apply online. Paper forms go to your local Social Security office by fax or mail. The split confuses people because the program, the website and the card all say Medicare, but the agency that processes enrollment is Social Security.

Medicare.gov publishes the rules; Social Security accepts the application and keeps the record. At Social Security. If you already have Part A, you sign up for Part B at SSA.gov (W8), and completed forms go to your local Social Security office by fax or mail (W9). Medicare.gov is where the rules live; Social Security is where the application lands.

What is form CMS-L564 and who fills it in?

It is the form your employer completes to confirm the job-based coverage you held, and it travels with your Part B application. It is the only step in the process whose timing is not under your control, which is why it should be started first rather than last.

If your employer cannot or will not complete it, there is a documented fallback: fill in Section B yourself as best you can, do not sign it, and submit proof of your job-based health insurance instead.

It is completed by the employer. If they cannot, you complete Section B unsigned and send proof of the job-based coverage instead (W16). Because it depends on somebody else's calendar rather than yours, it is the part to start first.

Will taking COBRA give me more time?

No, and this is the most common and most expensive misunderstanding in the whole process. Medicare states that COBRA is not considered group health plan coverage for this purpose, and that taking COBRA does not change when the Special Enrollment Period ends.

It also lists COBRA coverage ending among the situations that do not qualify for a Special Enrollment Period. Retiree coverage works the same way. Your clock runs from the end of the employment or the group plan, regardless of what you take afterwards.

No. COBRA is not group health plan coverage, and getting COBRA does not change when this Special Enrollment Period starts or ends (W7). COBRA ending is explicitly on the list of situations that do not qualify (W10).

Can I choose when Part B starts?

Within limits. Coverage generally begins 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, you can ask to delay the Part B start by up to three months.

It is a request made at the time, not an automatic setting. This is useful if you want the paperwork completed early but the premium starting later. Note that it expires much sooner than the eight month window, so treat it as its own shorter deadline.

Coverage generally begins the first month after you sign up (W4), so the lever is when you file rather than a start date you nominate. Signing up while still working, or within the first full month after the coverage ends, keeps the gap closed (W5).

What if I miss the window completely?

You wait for the General Enrollment Period, which runs from January 1 to March 31 each year, with coverage starting the month after you sign up, and you may pay a monthly late enrollment penalty.

Medicare explicitly lists a missed eight month window among the situations that do not qualify for another Special Enrollment Period, so there is no appeal for having misread the rule. Depending on when the window closed, the gap before coverage begins can run to several months on top of the penalty itself.

You wait for the General Enrollment Period, January 1 to March 31, with coverage starting the month after you sign up (W11, W12), and the penalty protection the Special Enrollment Period carried is gone (W13).