Still Working at 65?

Start with the size of the employer

This is the question that determines everything else, and it is about the employer providing the coverage, which may be your spouse's employer rather than yours.

• Twenty or more employees. The group health plan pays first and Medicare pays second. You can generally delay Part B for as long as that active employer coverage continues, and you will get a special enrollment period later with no late penalty.

• Fewer than twenty employees. Medicare generally pays first and the group plan pays second. Declining Part B in this situation can leave you very exposed, because the group plan may pay only what it would have paid after Medicare, and Medicare is not there. Confirm in writing with the plan administrator before you decline anything.

• Retiree coverage, a marketplace plan, TRICARE for Life, or VA care. None of these is active employer coverage, and the rules for each are different. Do not assume any of them protects your Part B timing.

Part A is a separate decision from Part B

Most people qualify for premium free Part A through their own or a spouse's work record. Because it costs nothing, taking it while you keep working is often the sensible default, and it can pick up hospital costs the group plan does not.

It is not automatic that this is right for everyone, though. There are situations in which enrolling in Part A while still covered by an employer plan has consequences you would want to know about first, and they depend on how your particular employer plan is built. We go through your plan documents with you rather than guess.

The three clocks that start when the job ends

This is where people are caught out, because the three windows are different lengths and they do not all start on the same day.

• Part B: eight months. Your special enrollment period runs eight months beginning the month after your employment ends or the month after the active group coverage ends, whichever comes first. Enroll within it and there is no Part B late enrollment penalty.

• Part D: two months. You get two months after your creditable prescription drug coverage ends to join a Part D plan without a late enrollment penalty. Two, not eight. This is the deadline most people blow past while they are still sorting out Part B.

• Medigap: 63 days. Losing employer group coverage gives you a guaranteed issue right to buy certain Medicare Supplement policies without medical underwriting, and that right lasts 63 days. Sixty three days goes quickly when you have just left a job.

Write the last day of coverage on a calendar the day you know it, and count forward three times.

Creditable coverage, and what the drug penalty really is

Creditable coverage means prescription drug coverage that is expected to pay, on average, at least as much as standard Medicare Part D. Employer plans are required to send you an annual notice saying whether yours is creditable. Ask for it, keep it, and keep the envelope it came in.

The Part D late enrollment penalty applies only after you have gone 63 or more days in a row without creditable drug coverage once you were eligible. Under 63 days and nothing happens. The penalty amount is calculated from the national base beneficiary premium, not from the price of the plan you eventually join, which is why choosing a cheap drug plan later does not shrink it. It is added for as long as you have Part D coverage.

The autumn window is not your window

October 15 to December 7 is the Annual Enrollment Period, and it is for people already on Medicare who want to change a drug plan or an Advantage plan. It is not the window for someone leaving employer coverage in March.

Your rights come from special enrollment periods, which run on your dates rather than on the calendar. That is a good thing: it means you do not have to wait. It also means nobody sends you a reminder, because there is no shared deadline to remind you of.