2027 Medicare Annual Enrollment Period: Key Dates & Checklist

If a Medicare Advantage plan denied a claim or made it hard to get the care you needed this year, you might be wondering if you're stuck with that plan forever. You're not. Once a year, Medicare gives everyone a chance to switch, and that window is coming up again soon. Here's exactly when it happens and how to get ready without the last-minute scramble.

When Is the 2027 Medicare Annual Enrollment Period?

The Medicare Annual Enrollment Period (AEP) for 2027 coverage runs from October 15 through December 7, 2026. Any change you make during this window takes effect on January 1, 2027.

This is sometimes called "Fall Open Enrollment," and it's separate from the Medicare Advantage Open Enrollment Period that happens in the first few months of the year. AEP is the big one — it's when you can make almost any change to your Medicare coverage, not just switch between Medicare Advantage plans.

Because dates and plan details can shift, always confirm the current AEP dates and any plan costs or benefit amounts directly at Medicare.gov or by calling 1-800-MEDICARE before you make a final decision.

What You Can Change During AEP

During the 2027 Annual Enrollment Period, you can:

• Switch from Original Medicare to a Medicare Advantage plan
• Switch from a Medicare Advantage plan back to Original Medicare
• Move from one Medicare Advantage plan to a different one
• Join, switch, or drop a Medicare Part D prescription drug plan

You can make as many changes as you want during the window — only your last change before December 7 counts for the new plan year. If you don't make any changes at all, your current coverage typically continues into 2027, though the plan itself may adjust its costs, drug list, or provider network for the new year. That's exactly why it's worth reviewing your coverage even if you're generally happy with it.

Why Even Happy Members Should Still Look

Plans can change their premiums, deductibles, drug formularies, and provider networks from one year to the next. A plan that worked well in 2026 might not cover the same doctors, hospitals, or medications in 2027. Reading your plan's Annual Notice of Change, which arrives every fall, is the fastest way to spot problems before they affect your care.

Why This Window Matters if You've Had a Denial or Coverage Problem

If you've dealt with a denied claim, a prior authorization delay, or a frustrating runaround with your Medicare Advantage plan, AEP is your chance to reset. You don't have to wait for something to go wrong again — you can proactively move to a plan whose prior authorization rules and provider network better fit your needs.

Before you switch, it helps to check your current plan's Evidence of Coverage and its separately published prior authorization list — not just the provider directory — to understand exactly what requires advance approval. Comparing that list across plans during AEP can help you avoid repeating the same denial next year.

It's also worth remembering: a denial doesn't have to be the final word. If you're appealing a current denial, don't give up simply because the process feels intimidating. A 2024 KFF analysis found that roughly 80% of appealed Medicare Advantage prior-authorization denials were overturned, even though a 2024 KFF analysis also found only about 11.5% of denied prior-authorization requests were ever appealed. In other words, many people who could benefit from appealing never do. Switching plans during AEP and pursuing an active appeal are not either/or — you can do both at the same time.

Know Your Notices: EOB vs. MSN

If you're comparing plans this fall, it helps to understand how you'll find out about a denial under each type of coverage. If you have Original Medicare, you'll receive a Medicare Summary Notice (MSN) listing your claims. If you're in a Medicare Advantage plan, you won't get an MSN at all — instead, your plan sends an Explanation of Benefits (EOB), and any formal denial arrives as a Notice of Denial of Medical Coverage or Payment (also called the Integrated Denial Notice). Knowing which document to expect helps you catch a denial early, whichever type of coverage you choose for 2027.

A Simple AEP Prep Checklist

You don't need to overhaul your entire understanding of Medicare to get ready for AEP. A little organization goes a long way.

Before October 15

• Gather your current plan's Annual Notice of Change letter once it arrives
• List every medication you take, including dosage and frequency
• List your regular doctors, specialists, and any hospital or facility you rely on
• Note any care you needed that was denied, delayed, or required prior authorization this year

During the Window (Oct 15–Dec 7, 2026)

• Use the Medicare Plan Finder at Medicare.gov to compare plans in your area
• Check that your doctors and hospitals are in-network for any plan you're considering
• Check that your medications are covered, and at what tier, for any plan you're considering
• Review each plan's prior authorization list for the specific services you use most
• Call 1-800-MEDICARE or your State Health Insurance Assistance Program if you have questions

After You Decide

• Confirm your enrollment or plan change was processed correctly
• Keep a copy of your confirmation for your records
• Watch for your new plan's welcome materials and ID card before January 1, 2027

What Happens After You Make a Change

Once your new coverage starts on January 1, 2027, your old plan's coverage ends. Keep both your old and new plan information handy for the first few weeks of the year, since claims for care received in late 2026 may still process under your old plan even after your new one begins.

If a claim is denied under your new plan, the appeal process still applies. For Medicare Advantage plans, a Level 1 appeal (called a Reconsideration) must generally be filed within 65 calendar days of the date on the denial notice — that's measured from the notice date itself, not from when you received it. If the plan upholds its denial, the case is automatically forwarded to the Independent Review Entity for a Level 2 review; you don't need to file anything separately for that step. Original Medicare appeals work differently, with a Level 1 Redetermination deadline of 120 calendar days from when you receive the notice. Because these deadlines differ by program and by appeal level, always check the specific deadline printed on your denial notice.

When to Get Help

Choosing between Original Medicare and Medicare Advantage, or comparing dozens of Advantage plans in your area, can feel overwhelming. You're not expected to do it alone. Your State Health Insurance Assistance Program offers free, unbiased counseling, and 1-800-MEDICARE can answer specific questions about your situation. If you're currently fighting a denial while also considering a plan switch, a Medicare appeals advocate or elder law attorney can help you understand your options without losing ground on either front.

The 2027 Annual Enrollment Period is a real opportunity to fix what didn't work this year. Mark your calendar for October 15 through December 7, 2026, start your checklist early, and don't let a past denial discourage you from either appealing it or finding a plan that fits your needs better next year.

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This article is general education, not legal or medical advice. Medicare rules, deadlines, and dollar amounts change; confirm the current details for your situation at Medicare.gov or by calling 1-800-MEDICARE. MedicareClaimDenied.com is not affiliated with or endorsed by Medicare, CMS, or any insurer.