The Initial Enrollment Period (IEP)
Your Initial Enrollment Period is your first chance to sign up for Medicare. It lasts 7 months: it starts 3 months before the month you turn 65, includes your birthday month, and ends 3 months after it. If you qualify for Medicare earlier because of a disability, ESRD or ALS, your timing is different; Medicare.gov has a separate path for each.
When your coverage starts depends on when in that window you act. Per Medicare.gov:
- If you have premium-free Part A, Part A starts the month you turn 65. (If your birthday is on the 1st, it starts the month before.)
- Sign up for Part B before your birthday month, and it starts the month you turn 65.
- Sign up during or after your birthday month, and Part B starts the month after you sign up.
During your IEP you can also join a Medicare Advantage plan or a Part D drug plan. If you join Advantage during your IEP, you have a second chance: within the first 3 months you have both Part A and Part B, you can switch to another Advantage plan or go back to Original Medicare.
Open Enrollment: October 15 – December 7
Medicare’s Open Enrollment Period (many people still call it the Annual Enrollment Period, or AEP) runs October 15 through December 7 every year. Whatever you choose takes effect January 1, as long as the plan receives your request by December 7. During this window you can:
- Join, drop or switch Medicare Advantage plans, with or without drug coverage.
- Move from Original Medicare to Medicare Advantage, or from Advantage back to Original Medicare.
- Join, drop or switch a standalone Part D plan if you are in Original Medicare.
Open Enrollment is when plan changes for the coming year are on the table. Your plan sends an Annual Notice of Change each fall; read it, then compare. Our guide on checking your doctors and drugs shows how to do that comparison properly.
One thing Open Enrollment does not do: it does not give you a guaranteed right to buy a Medigap policy. If you leave Advantage for Original Medicare in the fall, a Medigap insurer may be allowed to ask health questions. Plan that move carefully.
Medicare Advantage Open Enrollment: January 1 – March 31
If you are already enrolled in a Medicare Advantage plan, the Medicare Advantage Open Enrollment Period runs January 1 through March 31. It also applies within the first 3 months you have Medicare. You can:
- Switch to a different Medicare Advantage plan, with or without drug coverage.
- Drop your Advantage plan, return to Original Medicare, and join a separate drug plan.
Changes generally take effect the first of the month after the plan receives your request. This window is only for people already in Advantage; it cannot be used to move from Original Medicare into an Advantage plan, or to switch between standalone drug plans.
The General Enrollment Period: January 1 – March 31
If you missed your IEP and do not qualify for a Special Enrollment Period, the General Enrollment Period runs January 1 through March 31 each year. You can sign up for Part B, and for Part A if you have to buy it. Coverage starts the month after you sign up.
The catch is the late enrollment penalty. For Part B it is 10% for each full 12-month period you could have had Part B but did not, usually for as long as you have Part B. The math, with Medicare’s own examples, is in our late enrollment penalties guide.
Special Enrollment Periods (SEPs)
A Special Enrollment Period is a limited window opened by a specific life event. Medicare has two broad kinds.
SEPs for signing up for Part A and Part B
The one most Idahoans use is the 8-month Part B SEP for people who had group health coverage based on current work, their own or a spouse’s. It starts the month after the job or the coverage ends, whichever happens first. COBRA and retiree coverage are not coverage based on current work and do not extend it. See working past 65 for the details.
Medicare.gov also lists newer SEPs, including for people who lost Medicaid on or after January 1, 2023 (the window ends 6 months after Medicaid ends), people affected by a declared disaster or emergency, people given inaccurate information by an employer or health plan, and people released from incarceration. Most of these are requested with form CMS-10797 through Social Security.
SEPs for joining or switching plans
Separate SEPs let you join or change Medicare Advantage and drug plans after events such as moving to a new address, losing or changing other coverage, getting Medicaid, or getting Extra Help. If you sign up for Part A or B during an SEP for an exceptional situation, you have 2 months to join a plan.
Medigap Open Enrollment and Idaho’s Birthday Rule
Your Medigap open enrollment period is a one-time, 6-month window that starts when your Part B begins and you are 65 or older. During it, a Medigap insurer generally cannot turn you down or charge more because of your health. After it ends, insurers in most states can use medical underwriting.
Idaho adds a second chance. Under rules that took effect after February 28, 2022, Idaho Medigap policyholders may change plans each year on a guaranteed-issue basis during a 63-day window beginning on their birthday, according to the Idaho Department of Insurance. The new policy must have the same or fewer benefits; you cannot use it to upgrade. It does not help someone moving from Medicare Advantage to Medigap. More in Medicare Advantage vs. Medigap in Idaho.
All Medicare Windows at a Glance
| Window | Dates | What it is for |
|---|---|---|
| Initial Enrollment Period | 7 months around your 65th-birthday month | First sign-up for Parts A, B, Advantage and Part D |
| Open Enrollment | Oct. 15 – Dec. 7 | Change Advantage or drug plans for Jan. 1 |
| Medicare Advantage Open Enrollment | Jan. 1 – Mar. 31 | People already in Advantage: switch plans or return to Original Medicare |
| General Enrollment Period | Jan. 1 – Mar. 31 | Late Part B sign-up; coverage the month after |
| Part B SEP after work coverage | 8 months after job or coverage ends | Sign up for Part B without a penalty |
| Medigap open enrollment | 6 months from Part B start at 65+ | Buy Medigap without health questions |
| Idaho Medigap birthday rule | 63 days from your birthday, yearly | Existing Medigap holders: switch to equal or lesser coverage |
Want the longer, story-style version? Our blog post Medicare enrollment periods explained covers the same windows with real-life scenarios, and the enrollment window finder tells you which one applies to you today.
Which window are you in right now?
Give us your dates and current coverage and we will tell you what you can change, and by when, before any deadline passes.
Request a free comparison Call 208-350-9933Frequently Asked Questions
When is Medicare Open Enrollment for 2027 coverage?
Medicare’s Open Enrollment Period runs October 15 through December 7 every year. Changes you make during that window take effect January 1, so for 2027 plans the window is October 15 to December 7, 2026, and the plan must receive your request by December 7.
What can I change during the Medicare Advantage Open Enrollment Period?
If you are already in a Medicare Advantage plan on January 1, you can use January 1 to March 31 to switch to another Medicare Advantage plan, or drop your Advantage plan, return to Original Medicare and join a separate drug plan. It is not available to people in Original Medicare who want to join Advantage.
I missed my Initial Enrollment Period. What now?
You can sign up for Part B (and premium Part A) during the General Enrollment Period, January 1 to March 31 each year, with coverage starting the month after you sign up. A late enrollment penalty may apply unless you qualify for a Special Enrollment Period, for example because you had group coverage from current work.
How long do I have to sign up for Part B after my job coverage ends?
If you had group health coverage based on current work, yours or your spouse’s, you get an 8-month Special Enrollment Period that starts the month after the employment or the coverage ends, whichever comes first. COBRA or retiree coverage does not extend that 8-month window.
Is there an annual open enrollment for Medigap?
Not nationally. Federal law gives you one 6-month Medigap open enrollment period starting when your Part B begins and you are 65 or older. Idaho adds a birthday rule: people who already have a Medigap policy get a 63-day guaranteed-issue window each year starting on their birthday to switch to coverage of equal or lesser benefits.
Do Medicare Advantage and drug plan changes take effect immediately?
It depends on the window. Open Enrollment changes take effect January 1. Changes during the Medicare Advantage Open Enrollment Period and most Special Enrollment Periods generally take effect the first of the month after the plan receives your request.
Related Guides
Coverage pages for this topic: Medicare Advantage · Medicare Supplement · Medicare Part D. Other topics in the Learning Center: Health Insurance (ACA), Life Insurance, Final Expense, Annuities, Long-Term Care, Disability Insurance, Supplemental Health, Short-Term Medical, Travel Insurance.
Sources
- Medicare.gov — When does Medicare coverage start?
- Medicare.gov — Joining a plan (enrollment periods)
- Medicare.gov — Avoid late enrollment penalties
- Medicare.gov — Who pays first (coordination of benefits)
- Medicare.gov — What’s Medicare Supplement Insurance (Medigap)?
- Idaho Department of Insurance — Bulletin No. 21-04 (Medicare Supplement rating and eligibility)
- Idaho Department of Insurance — Recent changes to Medicare Supplement law and rules
Figures are labelled with the year they apply to and were checked against the official sources above on the review date. Rules and amounts change; confirm current figures with the agency that publishes them. This guide is general education, not individual advice.