October 15 is closer than it looks. That is the date Medicare's Annual Enrollment Period (AEP) opens, and it gives every California senior a limited window to change their Medicare coverage before the year ends. Waiting until mid-October to think about it means making a decision under time pressure. Starting to compare plans now, in the summer, means you walk into AEP with a clear picture of what you have, what changed, and whether a better option exists.
This guide explains exactly what AEP is, what you can change, what to review before October, and where to get help that does not cost you anything.
What Is the Medicare Annual Enrollment Period?
The Annual Enrollment Period runs from October 15 through December 7 every year. Any change you make during this window takes effect on January 1 of the following year. It is the primary opportunity Medicare gives you to reassess your coverage and make a switch.
AEP is not the same as the Open Enrollment Period for Marketplace coverage. It applies only to Medicare, and it is separate from other special enrollment windows like the Medicare Advantage Open Enrollment Period (January 1 to March 31), which is more limited in what you can do.
What You Can Change During AEP
During the Annual Enrollment Period, you can:
- Switch from Original Medicare (Parts A and B) to a Medicare Advantage plan
- Switch from a Medicare Advantage plan back to Original Medicare
- Change from one Medicare Advantage plan to a different one
- Join a Part D prescription drug plan if you do not already have one
- Switch from one Part D plan to another
- Drop a Part D plan entirely (though this may create a late-enrollment penalty if you go without drug coverage for more than 63 days)
Note: You cannot use AEP to buy or change a Medigap (Medicare Supplement) policy. Medigap changes are governed by separate enrollment rules and, in most states, require medical underwriting outside of guaranteed-issue periods. If you are considering Medigap, speak with an agent before AEP begins.
Why Summer Is the Right Time to Start
Most people wait until October to think about their Medicare plans, then feel overwhelmed when AEP opens. A summer review puts you in the driver's seat. Here is why it helps.
In September, insurance companies mail your Annual Notice of Change (ANOC). This letter describes every change your current plan is making for the coming year: premium increases, new copays, drugs being removed from the formulary, provider network changes. If you already know what you are looking for, you can read that letter in minutes and know whether to stay or shop.
In California, the Medicare Advantage market is competitive. Large counties like Los Angeles, San Diego, and the Bay Area often have dozens of plan options. Comparing them thoroughly takes time. Starting now means you are comparing, not scrambling.
Your Summer Medicare Checklist
Before October 15, review these four things:
- Pull out your current plan's Summary of Benefits and note your monthly premium, annual deductible, and primary care copay
- List every prescription you take and confirm each one is still on your plan's formulary (drug list) and in what tier
- Confirm your primary care doctor and any specialists you see regularly are still in your plan's network
- Think about what health services you expect to need in 2027 (surgery, physical therapy, new specialist) and whether your current plan handles them well
These four things take about 30 minutes and give you everything you need to compare plans intelligently once AEP opens.
The AEP Timeline for California Seniors
Now: Gather your information
List your drugs, doctors, and current plan costs. Note anything about your coverage that bothered you this year.
September: Read your ANOC letter
Your Annual Notice of Change arrives by mail. Check for premium increases, network changes, or drug tier changes. If something changed significantly, you know it is time to shop.
October 15: AEP opens
New plan year data is available. Use Medicare Plan Finder at Medicare.gov or work with a licensed agent to compare your options side by side.
December 7: AEP closes
Last day to enroll, switch, or drop a plan. Do not wait until the final week. Changes take effect January 1.
What Changes Most Often Between Plan Years
Plans are required to notify you of changes, but the ANOC letter can be dense. Watch for these four changes in particular:
Premium increases. Even a $20 monthly increase adds up to $240 per year. If your plan raised its premium, it is worth checking whether a similar plan in your area charges less.
Drug formulary changes. Plans can move drugs between tiers or remove them entirely each year. A drug you pay $10 for now could move to a tier that costs $80. This is one of the most common reasons people switch plans during AEP.
Provider network changes. Your plan can drop doctors or hospitals from its network. If your primary care physician leaves the network, you may need to find a new doctor or switch to a plan that still includes them. Our guide to Medicare Advantage in California explains how provider networks work and what to look for.
Extra benefits. Plans frequently add or remove dental, vision, hearing, or fitness benefits. If you are paying out of pocket for dental care, a plan with a dental benefit could save you significantly.
Free Help Available to California Seniors
You do not have to navigate this alone, and you do not have to pay for help. Two resources are available at no cost:
HICAP (Health Insurance Counseling and Advocacy Program) is California's free Medicare counseling service. HICAP counselors are trained, certified, and unbiased. They do not sell plans. You can reach HICAP through your county's Area Agency on Aging or at 1-800-434-0222.
Licensed Medicare agents are also free to use. Agents are paid by the insurance companies they represent, not by you. A good agent will walk you through plans across multiple carriers, compare costs for your specific drugs and doctors, and help you enroll. If you prefer Spanish-language guidance, our sister site Beneficios Medicare covers plan comparison topics in Spanish.
Want a head start before AEP opens?
A licensed Medicare specialist can review your current plan now and flag any gaps or costs to watch before October. No pressure, no fees.
Schedule a Free Plan ReviewFrequently Asked Questions
When is Medicare's Annual Enrollment Period in 2026?
AEP runs October 15 through December 7, 2026. Changes made during this period take effect January 1, 2027.
What can I change during Medicare Annual Enrollment?
You can switch between Original Medicare and Medicare Advantage, change from one Medicare Advantage plan to another, join or switch a Part D drug plan, or drop a Part D plan. All changes take effect January 1.
Do I have to do anything during AEP if I am happy with my plan?
No. If your plan is still offered and you are satisfied, you do not need to act. However, it is worth reading your Annual Notice of Change letter in September to make sure nothing important changed.
Where can I get free help comparing Medicare plans in California?
California's HICAP program offers free, unbiased counseling at 1-800-434-0222. You can also work with a licensed Medicare agent at no cost to you.
What is the Medicare Plan Finder?
It is a free comparison tool at Medicare.gov. Enter your zip code and your prescriptions and it shows estimated annual costs for each plan in your area. The most current plan data is available starting October 1 each year.
One More Thought
AEP only lasts 54 days. For a decision that affects your health coverage and costs for an entire year, 54 days goes fast. Starting your review now, even just by pulling together a list of your current drugs and doctors, means you will be ready when October arrives. A few hours of preparation can easily save hundreds of dollars and prevent coverage headaches down the road.