Medicare Enrollment Periods Explained for Arizona

Medicare has fixed windows for joining and changing coverage. Your Initial Enrollment Period is the seven months around your 65th birthday. The Annual Enrollment Period runs October 15 to December 7 each year, with changes starting January 1. The Medicare Advantage Open Enrollment Period, January 1 to March 31, lets people already in an Advantage plan make one change. The General Enrollment Period, also January 1 to March 31, is for people who missed Part A or Part B, with coverage starting the month after you sign up. Special Enrollment Periods cover life events like moving or losing job coverage. Right now, in the fall of 2026, Annual Enrollment is for choosing plans for 2027.

The windows at a glance

Initial Enrollment Period: your first window

Your IEP is built around the month you turn 65. For example, if you turn 65 on May 5, your IEP runs from February 1 through August 31. Sign up in February, March or April and your coverage starts May 1. Sign up in May or later and it starts the first of the following month.

If you qualify through disability, you have a similar seven-month window around your 25th month of disability benefits, and you get another IEP for Medicare Advantage and Part D when you turn 65.

Annual Enrollment Period: October 15 to December 7

This is the one time each year when everyone with Medicare can change their health and drug plans. During AEP you can:

• Switch from Original Medicare to a Medicare Advantage plan, or from Medicare Advantage back to Original Medicare.
• Switch from one Medicare Advantage plan to another, with or without drug coverage.
• Join, switch or drop a standalone Part D plan.

Medicare Advantage Open Enrollment: January 1 to March 31

If you are already in a Medicare Advantage plan on January 1, you get one more chance to change. You can move to a different Medicare Advantage plan, or leave Medicare Advantage for Original Medicare and join a standalone Part D plan. You can make only one change during this period, and it takes effect the first of the month after the plan receives your request. People with Original Medicare cannot use this window to join an Advantage plan.

General Enrollment Period: January 1 to March 31

If you missed your IEP and do not qualify for a Special Enrollment Period, the GEP is how you sign up for Part A or Part B. Since 2023, coverage starts the first of the month after you sign up, instead of waiting until July. A late enrollment penalty may still apply.

Special Enrollment Periods

Life events can open a window outside the usual dates. Common ones include:

• Losing employer or union group coverage based on current work. You have 8 months to sign up for Part B after the job or the coverage ends, whichever comes first, and generally 63 days to get drug coverage.
• Moving out of your plan's service area, or moving to a new area with different plan options, including moving to Arizona from another state.
• Moving into or out of a nursing home or other institution.
• Qualifying for AHCCCS (Arizona Medicaid), a Medicare Savings Program or Extra Help, which gives you additional chances to change coverage.
• Your plan leaving Medicare or your area, or Medicare ending its contract with your plan.
• The 5-star Special Enrollment Period, December 8 to November 30, to switch into a plan rated 5 stars. In the CY2027 CMS Landscape for Maricopa and Pinal counties, no Medicare Advantage plan carries a 5-star 2026 rating, so this one does not currently apply locally.

A year on the Medicare calendar

If you are already on Medicare, the year falls into a simple rhythm. In late September, your plan sends an Annual Notice of Change explaining what will be different next year. From October 1, plans can market next year's coverage and you can compare. October 15 to December 7 is the Annual Enrollment Period. Your choice starts January 1. From January 1 to March 31, Medicare Advantage members get one more change if the new plan is not working out.

For this year, that means 2027 plan details became available in the fall of 2026, and the CY2027 CMS Landscape file lists 52 Medicare Advantage plans in Maricopa County and 47 in Pinal County, plus 9 standalone Part D plans in Arizona. Your plan from 2026 renews automatically if it is still offered, so doing nothing is a choice too. It is just not always the right one.

The Medigap window, and why it is different in Arizona

Your Medigap Open Enrollment Period is a one-time, six-month window that starts the first month you are both 65 and enrolled in Part B. During it, any company selling Medigap in Arizona must sell you any policy it offers, at its standard price, regardless of health. If you delay Part B because you are still covered by an employer plan through current work, this window waits until you enroll in Part B.

Arizona does not add a yearly birthday or anniversary window on top of the federal rules (NAIC state chart, as of May 11, 2026). After your six months, you can still apply, but the company may use medical underwriting unless you have a federal guaranteed-issue right, such as your Medicare Advantage plan leaving the area or your employer coverage ending.

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The bottom line

Know which window you are in. If you are new to Medicare, it is your Initial Enrollment Period and your Medigap Open Enrollment Period. If you are already on Medicare, the Annual Enrollment Period from October 15 to December 7, 2026 is when you choose your 2027 plan. If something big changes in your life, ask whether it opens a Special Enrollment Period before you assume you have to wait.