Key takeaways
- There are four main Medicare enrollment windows: the Initial Enrollment Period (IEP), the Annual Enrollment Period (AEP), the Medicare Advantage Open Enrollment Period (MA OEP), and Special Enrollment Periods (SEPs).
- The AEP runs October 15 - December 7 every year; changes take effect January 1.
- The MA OEP runs January 1 - March 31 and is only for people already in a Medicare Advantage plan.
- Your IEP is a 7-month window around your 65th birthday - miss it and you may face lifelong penalties.
- SEPs open after qualifying life events like losing coverage or moving; timing varies.
- For context on cost, the standard 2026 Part B premium is $202.90/month with a $283 annual deductible.
Medicare has more than one enrollment window, and each one does something different. In short: your Initial Enrollment Period (IEP) is the 7-month window when you first sign up around age 65; the Annual Enrollment Period (AEP) runs October 15 - December 7 and is when most people review and change their coverage for the year ahead; the Medicare Advantage Open Enrollment Period (MA OEP) runs January 1 - March 31 for people already in a Medicare Advantage plan; and Special Enrollment Periods (SEPs) open outside those windows when a qualifying life event happens. Everything below is the detail behind those dates.
At TSM Life & Health, our philosophy is "educate first, plan second." This article is general education, not individualized advice. TSM is an independent insurance agency and is not connected with or endorsed by the government or the federal Medicare program. When you are ready to talk through your own situation, a licensed advisor can help - but let's start with the facts.
All the Medicare enrollment windows at a glance
Here is every major 2026 enrollment window, who it is for, the exact dates, and what you are allowed to do. Dates are confirmed against Medicare.gov.
| Window | Who it's for | 2026 dates | What you can do |
|---|---|---|---|
| Initial Enrollment Period (IEP) | People newly eligible (usually turning 65) | 7 months: the 3 months before your 65th-birthday month, that month, and the 3 months after | Sign up for Part A & B, Part D, or a Medicare Advantage plan for the first time |
| Annual Enrollment Period (AEP) | Anyone with Medicare | Oct 15 - Dec 7 (changes effective Jan 1, 2027) | Join, switch, or drop Medicare Advantage or Part D; move between Original Medicare and Medicare Advantage |
| MA Open Enrollment Period (MA OEP) | People already in a Medicare Advantage plan on Jan 1 | Jan 1 - Mar 31 | Switch to a different Medicare Advantage plan once, or drop it and return to Original Medicare + add Part D |
| General Enrollment Period (GEP) | People who missed their IEP for Part A/B | Jan 1 - Mar 31 | Sign up for Part A and/or Part B; coverage begins the first of the month after you enroll |
| Special Enrollment Period (SEP) | Anyone with a qualifying life event | Varies by event (e.g., 8 months after employer coverage ends) | Enroll in or change coverage outside the usual windows, often without a late penalty |
A quick note on sources. Every date and dollar figure here comes from Medicare.gov or CMS.gov. Rules can change, and your own plan's details always govern - confirm anything in writing before you enroll, and you can always call 1-800-MEDICARE or visit Medicare.gov for the full list of options.
Initial Enrollment Period (IEP): your first window
For most people, Medicare starts at 65. Your Initial Enrollment Period is a 7-month window that, according to Medicare.gov, begins 3 months before the month you turn 65, includes your birthday month, and ends 3 months after. Sign up in the first three months and your coverage generally starts the month you turn 65; sign up later in the window and coverage may start the month after you enroll.
This window matters more than any other, because missing it can cost you for life. If you do not sign up for Part B when first eligible and you do not have qualifying coverage from an employer, you can owe a Part B late-enrollment penalty - an extra 10% for each full 12-month period you could have had Part B - for as long as you have it. Part D has its own smaller lifelong penalty. If you are still working at 65 with employer coverage, you may be able to delay without penalty; that is a good moment to get advice.
Annual Enrollment Period (AEP): October 15 - December 7
This is the big one, and the window most people mean when they say "open enrollment." During the Annual Enrollment Period, anyone with Medicare can join, switch, or drop a Medicare Advantage plan or a stand-alone Part D drug plan, and move between Original Medicare and Medicare Advantage. Whatever you decide by December 7 takes effect January 1.
AEP is your yearly checkpoint. Each fall, carriers can change premiums, deductibles, drug formularies, pharmacy and provider networks, and extra benefits - so the plan that fit you last year may not be the best value next year. Read your plan's Annual Notice of Change (ANOC) when it arrives, list your medications and doctors, and compare total annual cost rather than premium alone. We walk through that habit in detail in our guide to Medicare's 2026 changes.
Medicare Advantage Open Enrollment Period (MA OEP): January 1 - March 31
The MA OEP is a common source of confusion because it sounds like AEP but is much narrower. Per Medicare.gov, it runs January 1 through March 31 and is only available if you are already enrolled in a Medicare Advantage plan on January 1. During it you can switch to a different Medicare Advantage plan once, or drop your Medicare Advantage plan and go back to Original Medicare (and pick up a Part D drug plan).
Think of the MA OEP as a safety valve, not a second shopping season. If you started the year in Original Medicare, you cannot use it to jump into Medicare Advantage. It exists mainly so that people who realize in January that their new plan is a poor fit have one chance to correct course.
Special and General Enrollment Periods
Life does not always line up with the calendar, which is why Medicare provides Special Enrollment Periods (SEPs). According to Medicare.gov, a qualifying life event opens a limited window to enroll in or change coverage, often without a late penalty. Common triggers include:
- Losing employer or other creditable coverage. When you (or your spouse) stop working, you get an 8-month SEP to sign up for Part B, and a shorter window to add a drug plan.
- Moving. If you move out of your plan's service area - or to an address with new plan options - you can change your Medicare Advantage or Part D plan.
- Losing your Medicare Advantage or Part D coverage. For example, when a plan leaves your area, an SEP typically lasts about 2 months after the coverage ends.
- Qualifying for Extra Help or Medicaid, entering or leaving a nursing facility, or other special circumstances.
Separately, the General Enrollment Period (GEP) runs January 1 - March 31 for people who missed their IEP and do not qualify for an SEP. You can sign up for Part A and/or Part B during the GEP, and your coverage begins the first of the month after you enroll. Because a late penalty may still apply, the GEP is a last resort - it is far better to use your IEP or an SEP.
Which window am I in? If you are turning 65, it's your IEP. If you already have Medicare and it's fall, it's AEP. If you already have a Medicare Advantage plan and it's the first quarter of the year, it's the MA OEP. If a life event just changed your coverage, ask whether an SEP applies - the answer is often yes.
The 2026 enrollment calendar, visualized
Most of the year has at least one window open. The chart below maps the calendar-based windows across 2026. (Your IEP is personal - it is built around your own 65th birthday - so it is not shown on the shared calendar.)
When each Medicare window is open across the year
Calendar-based enrollment windows, 2026
What Medicare costs in 2026 (so you can plan)
Enrollment decisions are easier when you know the numbers behind them. On November 2025, CMS announced the 2026 figures for Original Medicare. The standard Part B premium rose to $202.90 a month, up $17.90 from $185.00 in 2025, and the annual Part B deductible increased to $283. The Part A inpatient hospital deductible is $1,736 per benefit period. Higher-income beneficiaries pay more through IRMAA surcharges based on their 2024 income.
Standard Part B premium, 2023-2026
Monthly premium most beneficiaries pay (before any income surcharge)
None of this is one-size-fits-all. The "right" window - and the right plan within it - depends on your age, your current coverage, your medications, and your doctors. That is exactly what an annual review sorts out.
Not sure which enrollment window is yours?
Let's figure out your timing and review the plans available to you - no pressure, just plain answers. We'll compare your drugs, doctors, and budget against your options.
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Written by
Keith McLiverty
Keith is the founder and COO of TSM Life & Health, with more than 30 years in finance, taxes, medical insurance, and retirement planning. He believes in educating first and planning second, helping Connecticut families make confident, unhurried decisions about Medicare, Social Security, and protecting what they've built. This article is general education, not individualized advice.
Related reading
Sources & methodology
All dates and figures were verified against official U.S. government sources. Accessed July 31, 2026.
- When Can I Join, Switch, or Drop a Plan? (Enrollment Periods) - Medicare.gov
- When Does Medicare Coverage Start? (Initial Enrollment Period) - Medicare.gov
- Special Enrollment Periods - Medicare.gov
- Joining a Health or Drug Plan (AEP) - Medicare.gov
- 2026 Medicare Parts B Premiums and Deductibles - Centers for Medicare & Medicaid Services (CMS)
- Medicare Part B Premiums and Deductibles Will Increase in 2026 - U.S. Railroad Retirement Board (citing CMS)
- Understanding Medicare Advantage & Medicare Drug Plan Enrollment Periods - CMS