When to Sign Up for Medicare Turning 65 in Maricopa County, AZ: The Exact Step-by-Step Timeline — Before the $185/Month Penalty Clock Starts

By Diane Marshall, Turning 65 Bureau Chief — Scottsdale, Arizona  |  Published April 13, 2026  |  Updated April 13, 2026

Okay, friend. Let's just say it out loud: you Googled "when to sign up for Medicare" which means you're probably turning 65 soon, you have absolutely no idea how any of this works, and the alphabet soup of Part A, Part B, Part C, and Part D is making your head spin.

I've been here. I know exactly what this feels like. And I'm going to walk you through every single step — specifically for Maricopa County, Arizona — with real numbers, real local hospitals, real deadlines. By the end of this article, you'll know exactly what to do and when to do it.

Let's start at the very beginning.

What Is Medicare and Why Does Turning 65 Trigger a Deadline?

Medicare is the federal health insurance program for Americans 65 and older (and some younger people with disabilities). Unlike private insurance where you pick a plan during open enrollment at your job, Medicare has its own enrollment windows — and if you miss them, you pay more. Every month. For life. That's the part most people don't know until it's too late.

Here's the alphabet soup, decoded once and for all:

• Part A = Hospital insurance. Most people don't pay a premium for Part A if they've worked 10+ years.
• Part B = Medical insurance (doctor visits, outpatient care). This is where the $185.00/month premium comes in — and where the penalty bites if you're late.
• Part C = Medicare Advantage. A bundled plan sold by private insurers that combines A+B (and usually D). Think of it as an HMO or PPO that replaces Original Medicare.
• Part D = Prescription drug coverage. Separate plan you add on if you stay with Original Medicare (Parts A+B), or it may be bundled into your Part C plan.

When Exactly Does My Medicare Enrollment Window Open — And How Long Do I Have?

This is the part where most people panic, so I'm going to make it very clear.

Your Initial Enrollment Period (IEP) is a 7-month window built around your 65th birthday. Here's how it works:

The big takeaway from that chart: If you enroll in the 3 months BEFORE your birthday month, your coverage starts on the 1st of your birthday month — no gap. If you wait until your birthday month or after, your coverage is delayed by one to three months. That's months of being uninsured, or at minimum, months where you're still paying out of pocket for things Medicare would have covered.

Practical example: Let's say you turn 65 on September 15, 2026. Your IEP runs from June 1, 2026 through December 31, 2026. If you enroll in June, July, or August, your Part B starts September 1. If you wait until October, it doesn't start until December. And if you miss December 31 entirely without a qualifying reason, you'll wait until the next General Enrollment Period (January 1 – March 31 of the following year) and your coverage won't start until July 1 — plus you'll owe that penalty.

What Are the 6 Steps to Actually Enroll in Medicare in Maricopa County?

Okay, let's get practical. Here's the step-by-step process — no fluff, no filler.

1. 1
   Check if you'll be automatically enrolled If you're already receiving Social Security retirement benefits before you turn 65, you will be automatically enrolled in Medicare Parts A and B. Your red, white, and blue Medicare card will arrive in the mail about 3 months before your 65th birthday. You don't have to do anything except decide whether you want to keep Part B (you can decline it if you have qualifying employer coverage). If you're NOT yet drawing Social Security at 65, you must actively enroll.
2. 2
   Gather what you'll need Before you sit down to enroll, have ready: your Social Security number, date and place of birth, current health insurance information (employer coverage info if applicable), bank account info (if you want premiums auto-deducted), and the name and address of any employer where you or your spouse have current coverage.
3. 3
   Enroll in Parts A and B online, by phone, or in person The fastest way is online at ssa.gov/medicare. It takes about 10 minutes. You can also call Social Security at 1-800-772-1213 (TTY: 1-800-325-0778), Mon–Fri 8am–7pm. Or you can visit your local Social Security office — the Phoenix office is at 3443 N. Central Ave, Phoenix, AZ 85012; the Mesa office is at 1255 W. Baseline Rd, Mesa, AZ 85202.
4. 4
   Decide: Original Medicare (A+B) or Medicare Advantage (Part C)? Once you have Parts A and B, you choose your delivery system. Original Medicare lets you go to any doctor or hospital that accepts Medicare nationwide — great for snowbirds or frequent travelers. Medicare Advantage is a private plan (HMO, PPO) with network restrictions but often extra benefits like dental, vision, and gym memberships. Maricopa County has a competitive Medicare Advantage market with multiple major carriers. Compare plans at medicare.gov/plan-compare using your ZIP code.
5. 5
   Add a Part D drug plan (if you chose Original Medicare) If you go with Original Medicare (not Advantage), you need to separately enroll in a Part D prescription drug plan. Do this even if you don't take many drugs right now — the penalty for late enrollment is the same concept as Part B: 1% of the national base beneficiary premium for every month you were eligible but didn't enroll, added permanently. Don't skip this.
6. 6
   Consider a Medigap (Supplement) plan if you chose Original Medicare Medigap (officially "Medicare Supplement Insurance") fills the gaps in Original Medicare — copays, coinsurance, deductibles. Your best window to buy Medigap is during your 6-month Medigap Open Enrollment Period, which starts the month you're 65 AND enrolled in Part B. During this window, no insurer can deny you or charge you more based on health conditions. Miss this window and you may be medically underwritten — which matters a lot given that 23.5% of Maricopa County adults have arthritis and 5% have coronary heart disease. (Source: CDC PLACES 2023)

What Happens If I Miss My Enrollment Window — What Does the Late Penalty Actually Cost?

Source: CMS.gov 2026 Medicare costs. Penalty = 10% of standard premium per 12-month period of non-enrollment.

That extra money comes straight out of your Social Security check — they deduct it automatically. And when the standard premium goes up next year (it always does), your penalty percentage goes up with it.

I Still Work at 65 — Do I Actually Have to Sign Up for Medicare?

This is the single most common question I get from Maricopa County seniors, especially in the booming retirement communities around Sun City, Scottsdale, and Gilbert where many people are still working in their 60s.

Here's the short answer: it depends on how many people work at your company.

If your employer has 20 or more employees: Your employer plan is the primary payer. Medicare would be secondary. In this situation, you CAN delay Part B without penalty. You'll receive a Special Enrollment Period (SEP) — 8 months from when your employment or employer coverage ends, whichever comes first — to enroll in Part B without a penalty.

If your employer has fewer than 20 employees: Medicare becomes your primary insurer when you turn 65, even if you're still working and on the employer plan. Your employer plan becomes secondary. In this case, enroll in Medicare on time or risk significant coverage gaps.

Why Does Your Specific Maricopa County Health Profile Make Enrollment Timing So Important?

Here's where I get local with you. Maricopa County is a gorgeous place to retire — the sunshine, the desert, Banner Health around every corner — but our county has some real health challenges that make getting your