Medicare Enrollment: The Deadlines That Cost You Forever
Most health insurance mistakes are annual and recoverable. Medicare enrollment mistakes are permanent. The late enrollment penalties are added to your premium for as long as you have the coverage, which means for the rest of your life.
The windows
| Period | When | What it does |
|---|---|---|
| Initial Enrollment Period | Seven months: three before your 65th birthday month, that month, three after | Your first chance to enroll in A, B, C and D |
| Special Enrollment Period | While covered by active employment, and for eight months after it ends | Lets you delay Part B without penalty |
| General Enrollment | Early in each year | The catch-up window if you missed everything, with penalties applying |
| Annual Open Enrollment | Autumn each year | Change Advantage and Part D plans for the following year |
| Medicare Advantage Open Enrollment | Early each year | One switch out of or between Advantage plans |
COBRA and retiree coverage do not protect you. The Part B special enrollment period requires coverage based on current, active employment — yours or a spouse's. COBRA is not active employment. Neither is retiree coverage. People delay Part B on COBRA every year believing they are safe, and inherit a permanent penalty plus a gap in coverage. If you are on COBRA and turning 65, enroll in Part B.
The penalties, concretely
- Part B: a percentage added to your premium for each full 12-month period you could have had it and did not. It never goes away.
- Part D: a smaller amount based on how many months you went without creditable drug coverage, added permanently to your Part D premium.
- Part A, if you have to buy it, has its own penalty structure.
The Part D trap catches healthy people who take no medication and see no reason for drug coverage. The penalty accrues anyway. A minimal Part D plan is cheap insurance against a permanent surcharge.
What to do, in order
- Three months before turning 65, confirm in writing with your employer whether your coverage is creditable and whether it counts as active employment.
- Decide the architecture: Original plus Medigap plus Part D, or Advantage. Do this before enrolling, because the Medigap window matters.
- Enroll in the Initial Enrollment Period unless you have confirmed active-employment coverage.
- Buy Medigap during your guaranteed-issue window if you are going the Original route — see below.
- Enroll in Part D even if you take nothing, unless you have creditable drug coverage.
The Medigap window is the most consequential deadline nobody mentions. For six months starting when you are 65 and enrolled in Part B, you have a guaranteed right to buy any Medigap policy sold in your state, regardless of health. After that, in most states, insurers may underwrite — and can decline you or charge more. A decision that felt reversible at 65 frequently is not at 70.
Frequently Asked Questions
Am I enrolled automatically?
If you are already receiving Social Security benefits, generally yes for A and B. Otherwise you must actively enroll.
What if I'm still working at a small employer?
Below a size threshold, Medicare becomes primary and you generally need Part B at 65. Confirm the specific rule with the employer.
Can a penalty be waived?
Rarely, in cases involving bad information from a federal employee, through a formal equitable relief request. Do not plan around it.
Does my spouse enroll separately?
Yes. Medicare is individual. A spouse may qualify on your work record, but enrolls on their own timeline.
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