Medicare has at least five enrollment windows with overlapping dates, different eligibility rules, and different consequences for missing them. Here is what each one covers and when it applies to you.
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Five windows. Different rules. Here is the full picture.
| Period | Dates | Who it's for | What you can do |
|---|---|---|---|
| Initial Enrollment Period (IEP) | 7 months around your 65th birthday | People turning 65 or first becoming eligible | Enroll in Parts A, B, and D; join a Medicare Advantage plan |
| Annual Open Enrollment (OEP) | October 15 through December 7 | Anyone currently enrolled in Medicare | Switch between Original Medicare and Medicare Advantage; change drug plans |
| General Enrollment Period (GEP) | January 1 through March 31 | People who missed their IEP | Enroll in Part A and Part B (coverage starts July 1); late penalties apply |
| Medicare Advantage OEP (MA-OEP) | January 1 through March 31 | People already in a Medicare Advantage plan | Switch Advantage plans or return to Original Medicare plus Part D |
| Special Enrollment Period (SEP) | Varies by qualifying event | People with a qualifying life event | Enroll or change coverage outside normal windows; no penalty in most cases |
Your IEP spans 7 months: 3 months before the month you turn 65, your birthday month, and 3 months after. If your birthday is in June, your IEP runs March 1 through September 30. Enrolling in the first 3 months means coverage starts on the first day of your birthday month. Wait until the last 3 months and coverage is delayed by 1 to 3 months.
Missing your IEP entirely is the most expensive mistake in Medicare. You will have to wait for the General Enrollment Period, and a late enrollment penalty gets added to your premium permanently.
This is the yearly window when everyone on Medicare can review and change their coverage. You can switch from Original Medicare to Medicare Advantage (or back), change your Part D drug plan, or join a drug plan if you don't have one. Changes made during this period take effect January 1 of the following year.
Premiums, formularies, and provider networks change every year. Even if you are happy with your current plan, reviewing it during Open Enrollment can save hundreds annually. According to KFF, about 70% of Medicare Advantage enrollees have access to a lower-premium plan but do not switch (KFF Medicare Advantage Report, 2024).
A Special Enrollment Period lets you enroll or change coverage outside the standard windows. The most common trigger is losing employer-based health insurance. If you or your spouse had coverage through a current employer, you get an 8-month SEP after that coverage ends. This is why many people who work past 65 delay Part B enrollment without penalty.
Other qualifying events include moving out of your plan's service area, losing Medicaid eligibility, qualifying for Extra Help (Low Income Subsidy), or leaving a skilled nursing facility. The length and rules of each SEP vary. Check with Social Security at 1-800-772-1213 to confirm your eligibility.
Set a Medicare enrollment reminder for the enrollment period that applies to you. The reminder fires before the window opens, giving you time to review your options. It recurs yearly so you never have to remember which month to start looking.
Already missed a window? Read about the most common Medicare enrollment mistakes and how to recover.
The three most important are the Initial Enrollment Period (7 months around your 65th birthday), the Annual Open Enrollment Period (October 15 through December 7), and the General Enrollment Period (January 1 through March 31). Each serves a different purpose and missing one may mean waiting months for the next.
ICEP stands for Initial Coverage Election Period. It is functionally the same as the Initial Enrollment Period. It is the 7-month window when you first become eligible for Medicare, centered on the month you turn 65.
Yes, during the Medicare Advantage Open Enrollment Period (January 1 through March 31). You can switch to a different Advantage plan or return to Original Medicare. If you return to Original Medicare, you can also join a standalone Part D drug plan during this window.
Two periods overlap in this window. The General Enrollment Period lets people who missed their IEP sign up for Part A and Part B (coverage starts July 1). The Medicare Advantage Open Enrollment Period lets current Advantage enrollees switch plans or return to Original Medicare (changes take effect the first of the following month).
Qualifying events include losing employer coverage, moving out of your plan's service area, losing Medicaid eligibility, or being released from incarceration. You typically get 8 months after losing employer coverage to enroll without a penalty. Check with Social Security to confirm your specific situation.
If you are approaching 65, set a reminder for 3 months before your birthday to start your Initial Enrollment Period. If you are already on Medicare, set a recurring reminder for early October so you review your plan before Open Enrollment closes December 7.
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