The four Medicare enrollment windows, and which one you are in

Almost every Medicare problem we are asked to fix started as a date somebody did not know applied to them. The rules themselves are not complicated. Knowing which of the four windows you are standing in is most of the work.

The Initial Enrollment Period

This is the one that opens around your 65th birthday. It runs for seven months: the three months before the month you turn 65, the birthday month itself, and the three months after.

Two things about it catch people out.

The first is that enrolling early and enrolling late are not symmetrical. Sign up in the three months before your birthday month and coverage generally starts at the beginning of your birthday month. Sign up in the months after, and the start date pushes back. The window is seven months long but the useful part of it is the front.

The second is that it is tied to your birthday, not to a season. It has nothing to do with the autumn enrollment period you see advertised, and the two get conflated constantly.

The General Enrollment Period

If you missed your Initial window and you have no other qualifying coverage, this is the fallback. It runs in the first quarter of each year.

It is a safety net rather than a good outcome. Coverage starts later than it would have, and a late-enrollment penalty may attach — one that, for Part B, can stay with you permanently rather than expiring. We will not print the penalty formula here because it changes; ask us or ask 1-800-MEDICARE for the current one.

If you are reading this because you already missed a window, the useful next step is a phone call rather than more reading. There are exceptions, and whether one applies to you turns on facts we would need to hear.

The Open Enrollment Period

This is the autumn one, and it is the only window most people have heard of. It is for people already on Medicare who want to change something: switch between Original Medicare and Advantage, change Advantage plans, or join, drop or switch a Part D drug plan.

It is not a window for joining Medicare for the first time. That distinction matters because the advertising in that season does not make it.

The thing worth doing in this window, every single year, is a formulary check. Drug plans revise their covered-drug lists annually. A plan that covered your prescription this year may not next year, and the letter telling you so is easy to miss in the volume of post that arrives each autumn.

Special Enrollment Periods

These are triggered by a life event rather than a date on the calendar. The common triggers:

• Losing employer coverage — yours or a spouse’s, through retirement or job loss.
• Moving out of your plan’s service area.
• Your plan leaving your area, or ending its contract.
• Becoming eligible for Medicaid or for a programme that helps with drug costs.
• Entering or leaving an institution such as a nursing facility.

Each has its own length and its own start trigger, and the clock usually runs from the event rather than from when you found out. That is the part people lose time to.

The one that catches working people

If you are still working at 65 with employer coverage, whether you should take Part B depends on how large the employer is. Above a certain headcount, the employer plan generally pays first and delaying Part B is usually safe. Below it, Medicare generally pays first, and delaying can leave you with claims nobody covers — retroactively.

We have seen this go wrong more than any other single thing on this page, and it is almost always the same story: an HR department said “you can stay on our plan” and was answering a different question than the one that mattered.

Before you decide, ask your employer plan administrator one specific question in writing: is this coverage creditable, and does it pay primary or secondary to Medicare for someone my age at a company this size? Get the answer in writing.

What to actually do

1. Work out which window you are in from the descriptions above.
2. If it is the Initial window, act in the first half of it rather than the second.
3. If you are still working, get the creditable-coverage answer in writing before you decide anything.
4. If you are in the autumn window and already enrolled, re-check your prescriptions against next year’s formulary. Every year, without exception.

If you would rather have someone walk it with you, that is what we do, and it costs you nothing. If your situation is simple, the Medicare Plan Finder or a free SHIP counsellor will get you the same answer.