Every fall, Medicare beneficiaries get a window to rethink their health coverage — and most people either don't use it or don't fully understand what they're allowed to change. The Annual Enrollment Period, which runs from October 15 through December 7, is the single most important stretch of time in the Medicare calendar. During these 54 days, you can make changes that affect your premiums, your drug costs, your network of doctors, and your out-of-pocket exposure for the entire coming year. Missing it, or making the wrong move, can lock you into a plan that doesn't serve you well for twelve months.
Let's start with the basics of who this enrollment period is for. The AEP applies to people who are already enrolled in Medicare — either Original Medicare (Parts A and B) or a Medicare Advantage plan. It is not the same as your Initial Enrollment Period, which is the seven-month window around your 65th birthday when you first sign up for Medicare. If you're turning 65 and enrolling for the first time, your timeline is different. The AEP is specifically for people who already have Medicare coverage and want to make changes to that coverage going forward.
During the AEP, you have several distinct options. You can switch from Original Medicare (Parts A and B) to a Medicare Advantage plan (Part C). You can do the reverse — drop a Medicare Advantage plan and return to Original Medicare. You can switch from one Medicare Advantage plan to a different Medicare Advantage plan. You can enroll in a standalone Medicare Part D prescription drug plan if you don't already have one. You can switch from one Part D plan to a different Part D plan. Or you can drop your Part D coverage entirely, though doing so without creditable drug coverage elsewhere can trigger a late enrollment penalty later. Each of these changes takes effect on January 1 of the following year.
One of the most common mistakes beneficiaries make is assuming their current plan will stay the same from year to year. It won't — at least not necessarily. Medicare Advantage and Part D plans are allowed to change their premiums, deductibles, copays, drug formularies, and provider networks every January 1. Your plan is required to send you an Annual Notice of Change (ANOC) by September 30 each year, which details every modification coming in the new plan year. Reading that document carefully before October 15 is essential. If your doctor is being dropped from the network, or a drug you take is moving to a higher cost tier, you need to know that before the AEP closes on December 7.
According to CMS.gov data, in 2024 there were 7,543 Medicare Advantage plans available nationwide, with an average monthly premium of approximately $18.50 for plans that include drug coverage — a figure that has fluctuated year over year as insurers adjust their bids to CMS. The number of plans available in any given county varies dramatically: beneficiaries in urban areas like Miami-Dade County, Florida, or Los Angeles County, California, may have access to 60 or more plans, while rural beneficiaries in parts of Wyoming or Montana may have fewer than five. CMS.gov's Medicare Plan Finder tool, available at medicare.gov/plan-compare, is the most reliable way to see exactly which plans are available at your specific zip code and compare their costs side by side.
For people on Original Medicare who are considering switching to Medicare Advantage during the AEP, the financial calculus deserves careful thought. Medicare Advantage plans often advertise $0 premiums, and many do carry no monthly premium beyond what you already pay for Part B — which in 2025 is $185.00 per month for most beneficiaries. But zero premium does not mean zero cost. Medicare Advantage plans typically have copays for specialist visits, hospital stays, and procedures, plus an annual out-of-pocket maximum that can range from roughly $3,500 to $8,850 in-network for 2025 plans. If you're healthy and rarely use medical services, a low-premium MA plan may save you money. If you have chronic conditions and see multiple specialists regularly, the copay structure of an MA plan can add up quickly compared to Original Medicare paired with a Medigap supplement.
Speaking of Medigap — this is where the AEP gets complicated for people who want to switch back to Original Medicare. If you're currently in a Medicare Advantage plan and want to return to Original Medicare during the AEP, you can do so. But if you also want a Medigap policy to cover Original Medicare's cost-sharing gaps, you may face medical underwriting in most states. That means the Medigap insurer can review your health history and potentially deny you coverage or charge you higher premiums based on pre-existing conditions. The guaranteed issue rights that protect you when you first turn 65 generally do not apply when you voluntarily leave a Medicare Advantage plan after your first year. There are exceptions — if your MA plan is leaving your area or loses its Medicare contract, you have guaranteed issue rights to buy certain Medigap plans. But in most voluntary switch scenarios, your health status matters.
Thirteen states have enacted what's known as a birthday rule, which gives Medigap policyholders a 30-day window around their birthday each year to switch to a Medigap plan of equal or lesser benefits without medical underwriting. Those states are California, Idaho, Illinois, Kentucky, Louisiana, Maine, Maryland, Missouri, Nevada, New Jersey, New York, Oklahoma, and Oregon. If you live in one of these states and are considering moving from Medicare Advantage back to Original Medicare with a Medigap supplement, your birthday window may give you a protected path to do so — though the specifics vary by state, so checking with your state insurance department is worthwhile.
The Part D prescription drug piece of the AEP deserves its own focused attention. Even if you're happy with your Medicare Advantage plan and have no intention of switching, you should still review your Part D coverage every year. Drug formularies — the list of medications a plan covers and at what cost tier — change annually. A medication you paid a $10 copay for in 2025 might move to a tier that costs $45 in 2026. The Medicare Plan Finder allows you to enter your specific medications and dosages and compare what each available plan would actually cost you for those drugs over the course of a year, including premiums, deductibles, and copays. This is the single most useful exercise you can do during the AEP, and it takes about 20 minutes.
For 2025, the standard Part D deductible is $590 — though many plans charge less or waive it for certain drug tiers. The out-of-pocket cap for Part D was set at $2,000 for 2025 under the Inflation Reduction Act, a significant change from prior years when catastrophic drug costs had no hard ceiling. This cap means that once you've spent $2,000 out of pocket on covered drugs in a plan year, your plan covers 100% of additional drug costs for the rest of the year. This change makes Part D coverage more valuable than it has been historically, particularly for beneficiaries who take expensive specialty medications.
There is a second enrollment window that many beneficiaries confuse with the AEP: the Medicare Advantage Open Enrollment Period, which runs January 1 through March 31. This OEP is more limited in scope. During the OEP, you can switch from one Medicare Advantage plan to another, or you can drop your Medicare Advantage plan and return to Original Medicare (with the option to add a standalone Part D plan). What you cannot do during the OEP is switch from Original Medicare to Medicare Advantage, or make changes to a standalone Part D plan if you're already on Original Medicare. The OEP exists primarily as a safety valve for people who made a change during the AEP and quickly realized it wasn't working for them.
Special Enrollment Periods exist outside both the AEP and OEP for people who experience qualifying life events. Moving out of your plan's service area, losing employer coverage, qualifying for Extra Help (the Low Income Subsidy program), or having your plan terminated by Medicare can all trigger an SEP that allows you to make changes outside the standard windows. The duration and scope of each SEP depends on the triggering event, and not all SEPs allow the same range of changes. If you think you may qualify for an SEP, calling 1-800-MEDICARE (1-800-633-4227) directly is the most reliable way to confirm your eligibility and understand your options.
For beneficiaries who want help navigating the AEP without sales pressure, State Health Insurance Assistance Programs — known as SHIPs — offer free, unbiased counseling in every state. SHIP counselors are trained volunteers and staff who can walk you through plan comparisons, explain your rights, and help you understand your Annual Notice of Change. You can find your local SHIP through the Medicare.gov website or by calling 1-800-MEDICARE. These counselors have no financial stake in which plan you choose, which makes them a genuinely useful resource during a period when you'll also be receiving a flood of marketing materials from insurance companies.
The bottom line for the 2026 AEP is this: don't assume your current coverage is still the best fit. Read your Annual Notice of Change when it arrives in late September. Use the Medicare Plan Finder to compare drug costs with your actual medication list. If you're on Medicare Advantage, verify that your doctors and preferred hospitals are still in-network for the coming year. And if you're considering a major switch — particularly from Medicare Advantage back to Original Medicare — understand the Medigap underwriting rules in your state before you make that move. The AEP closes at midnight on December 7, and changes made after that date won't take effect until the following year's enrollment cycle.