Medicare enrollment confuses people because there isn't one deadline — there are several windows, each with a different purpose. Here's which is which.
IEP — Initial Enrollment Period
Your first opportunity, and it's seven months long: the three months before your 65th birthday month, your birthday month, and the three months after.
Enrolling in the earlier part of that window generally means coverage starts sooner. Missing it without other qualifying coverage can mean late enrollment penalties that follow you permanently — not a one-time fee, but an increase to your premium for as long as you have the coverage.
If you're still working at 65 with employer coverage, the rules differ. That's a conversation worth having before your birthday rather than after.
Medigap Open Enrollment — the one people miss
Separate from everything else, and the one I most often wish people had known about. It's a six-month window beginning when you're 65 or older and enrolled in Part B.
During it you can buy a Medicare Supplement with no health questions. After it closes, in most states a carrier can consider your health and decline you. It is the single easiest window to let pass quietly and the hardest to get back.
AEP — Annual Enrollment Period
October 15 to December 7, every year. This is when you can change your Part D drug plan or your Medicare Advantage plan, with the new coverage starting January 1.
Even if you're happy, this is the right moment for a review — plans change their formularies, networks and costs every year, and the plan that fit you last year may not this year.
OEP — Open Enrollment Period
January 1 to March 31, for people already enrolled in a Medicare Advantage plan. You get one change: switch to a different Advantage plan, or return to Original Medicare and add a drug plan.
It exists precisely because people sometimes discover in January that the plan they chose isn't what they expected.
SEP — Special Enrollment Period
Life doesn't wait for October. A range of circumstances open their own window, each under its own SEP code:
- Moving out of your plan's service area
- Losing employer or union coverage
- Your plan leaving your area or ending its contract
- A change in Medicaid or Extra Help eligibility
- Moving into or out of a nursing facility
Many people qualify for a Special Enrollment Period without realizing it. If something significant has changed in your circumstances, it's worth asking rather than assuming you have to wait.
Not sure which applies to you?
Worth saying plainly: the Medigap window is the one I see people lose most often, usually because nobody told them it existed. It runs six months from when you're 65 and on Part B, and once it closes, a carrier can look at your health and say no. If you are anywhere near that window, it is worth a conversation now rather than in the autumn.
That's a short phone call, and there's no cost to it. Bringing it up early is almost always better than bringing it up late — several of these windows cannot be reopened once they close.