Medicare’s main Open Enrollment Period runs October 15 through December 7 every year, and changes you make take effect January 1 of the following year. The next window — October 15 to December 7, 2026 — is when you can change your coverage for 2027. This is the one guaranteed window each year when anyone with Medicare can switch plans, no health questions asked — but it’s easy to confuse with two other Medicare enrollment windows that work differently. Here’s exactly what the dates mean, what you can and can’t change, and where people lose money by acting too late or too casually.
When Is Medicare Open Enrollment?
- Fall Open Enrollment (Annual Election Period): October 15 – December 7, 2026. Changes made during this window start January 1, 2027.
- Medicare Advantage Open Enrollment Period: January 1 – March 31 each year. A separate, more limited window (explained below).
- General Enrollment Period: January 1 – March 31 each year. For people who missed signing up for Part A and/or Part B when first eligible.
The October–December window is what most people mean when they say “Medicare Open Enrollment,” and it’s the one that gets advertised heavily on TV each fall. According to Medicare.gov, you’ll get an “Evidence of Coverage” and “Annual Notice of Change” letter from your current plan every September — read it. Premiums, drug formularies, and provider networks can all change from one year to the next, even if you do nothing.
Why This Window Exists
Medicare plans — Medicare Advantage and Part D drug plans in particular — are run by private insurers under contract with CMS (Centers for Medicare & Medicaid Services). Those contracts get renewed annually, and insurers can adjust premiums, copays, covered drugs, and provider networks each year. The fall window exists so you have a predictable, once-a-year chance to react to those changes without needing to qualify for a special circumstance.
What You Can Actually Change (Oct 15 – Dec 7)
During Fall Open Enrollment, you can:
- Switch from Original Medicare to a Medicare Advantage plan
- Switch from a Medicare Advantage plan back to Original Medicare
- Switch from one Medicare Advantage plan to a different one
- Switch from one Part D prescription drug plan to another
- Enroll in a Part D plan for the first time
- Drop Part D coverage entirely (though this can trigger a late enrollment penalty later if you don’t have other creditable drug coverage)
What it does not let you do: enroll in Medicare for the first time if you’re not otherwise eligible, or get guaranteed-issue rights to buy a Medigap (Medicare Supplement) policy. Medigap has its own rules, discussed below, and they trip up a lot of people who assume this window covers everything.
The Other Windows People Confuse With This One
This is where costly mistakes start. Here’s how the major Medicare enrollment periods compare:
| Enrollment Period | Dates | Who It’s For | What You Can Do |
|---|---|---|---|
| Initial Enrollment Period | 7 months around your 65th birthday (3 before, birthday month, 3 after) | First-time Medicare enrollees | Sign up for Part A and/or Part B |
| Fall Open Enrollment (AEP) | Oct 15 – Dec 7 each year | Anyone with Medicare | Switch Medicare Advantage, Part D, or return to Original Medicare |
| Medicare Advantage Open Enrollment Period | Jan 1 – Mar 31 each year | People already enrolled in a Medicare Advantage plan | One switch: to another MA plan, or back to Original Medicare (can add a Part D plan if doing so) |
| General Enrollment Period | Jan 1 – Mar 31 each year | People who missed their Initial Enrollment Period | Sign up for Part A and/or Part B (coverage starts the month after enrollment) |
| Special Enrollment Period | Varies, tied to a qualifying event | People who lost coverage, moved, etc. | Depends on the event — check Medicare.gov |
The Medicare Advantage Open Enrollment Period (Jan 1–Mar 31) is the one people mix up most. It only applies if you’re already in a Medicare Advantage plan, it only allows one change, and it does not let you switch Part D plans independently if you’re on Original Medicare. If you’re on Original Medicare with a standalone Part D plan and miss the December 7 deadline, you generally cannot change that drug plan until the following fall — a full year stuck with whatever formulary and premium you have, unless you qualify for a Special Enrollment Period.
Costly Mistakes People Make
1. Assuming “no news is good news.” If you don’t act, you stay on your current plan automatically. That’s fine only if you’ve actually confirmed your drugs, doctors, and costs aren’t changing for the coming year. Insurers routinely adjust formularies, tiers, and provider networks each January, according to CMS.
2. Not checking the drug formulary line by line. A Part D or Medicare Advantage plan that was your cheapest option this year can become one of the pricier ones next year if your medication moves to a higher tier or gets dropped. Medicare’s Plan Finder tool at Medicare.gov lets you enter your specific medications and compares total annual cost, not just premium.
3. Assuming Medigap works like Part D. Medigap (Medicare Supplement) policies are not part of this window at all. You typically get a one-time, six-month guaranteed-issue right to buy Medigap starting the month you’re 65 and enrolled in Part B. Outside that window, insurers in most states can use medical underwriting to deny you or charge more based on health conditions. A few states (like New York and Connecticut) have their own rules extending guaranteed issue — check with your State Health Insurance Assistance Program (SHIP) for your state’s specifics.
4. Switching to Medicare Advantage without checking the network. Original Medicare works with any provider that accepts Medicare, nationwide. Medicare Advantage plans use networks, and some require referrals or prior authorization. If you switch to Advantage and later want to go back to Original Medicare plus Medigap, you may face medical underwriting for the Medigap policy (see mistake #3), which can leave you without supplement coverage if you have health issues.
5. Missing the December 7 deadline because of paperwork delays. Plan changes made online or by phone at Medicare.gov or 1-800-MEDICARE are processed based on when you submit them, not when they’re confirmed. Don’t wait until December 6 to start comparing plans.
6. Ignoring Part B and Part D late enrollment penalties. If you didn’t sign up for Part B when first eligible and don’t have other creditable coverage (like current employer coverage), your premium can permanently increase by 10% for each 12-month period you delayed. Part D has a similar penalty structure based on months without creditable drug coverage. According to SSA.gov and Medicare.gov, these penalties last as long as you have the coverage — they don’t expire.
How to Review Your Plan Before December 7
- Read your Annual Notice of Change letter from your current plan, sent every September.
- List your current medications, dosages, and pharmacies.
- Use the Medicare Plan Finder at Medicare.gov to compare next year’s plan costs using your actual drug list (2027 plan details appear by early October 2026).
- Check that your doctors and hospitals are in-network if you’re considering or staying with a Medicare Advantage plan.
- Call your State Health Insurance Assistance Program (SHIP) for free, unbiased one-on-one help — this is a federally funded counseling service, not a sales line.
- Make your decision by December 7 and confirm you receive a confirmation notice for any change.
How to Apply or Switch Plans
You can make changes three ways:
- Online: Medicare.gov, using your Medicare account
- By phone: 1-800-MEDICARE (1-800-633-4227), available 24/7
- Directly through the plan you’re enrolling in, or through a licensed agent
If you’re switching Medicare Advantage or Part D plans, you generally don’t need to cancel your old plan yourself — enrolling in a new one automatically disenrolls you from the old one, effective January 1.
FAQ
What happens if I miss the December 7 deadline?
You’ll generally keep your current Medicare Advantage or Part D plan for the entire following year. Your next chance to make a broad change is the following fall, unless you qualify for a Special Enrollment Period (for example, moving out of your plan’s service area or losing employer coverage) or, if you have Medicare Advantage, the narrower Jan 1–Mar 31 Medicare Advantage Open Enrollment Period.
Can I switch from Medicare Advantage back to Original Medicare during fall Open Enrollment?
Yes. You can drop Medicare Advantage and return to Original Medicare during the October 15–December 7 window, effective January 1. Keep in mind that adding a Medigap policy at that point isn’t guaranteed — insurers can use medical underwriting unless you qualify for a guaranteed-issue right or live in a state with expanded protections. Check with your SHIP office before making the switch.
Is Medicare Open Enrollment the same as the ACA Marketplace Open Enrollment?
No. They’re separate programs with separate dates and rules. Medicare’s fall Open Enrollment (Oct 15–Dec 7) covers Medicare Advantage and Part D changes for people already on Medicare. The Affordable Care Act Marketplace at HealthCare.gov has its own open enrollment period, typically November 1–January 15 in most states, for people under 65 or not otherwise eligible for Medicare.
Sources
- Medicare.gov — Official U.S. government site for Medicare (medicare.gov)
- CMS.gov — Centers for Medicare & Medicaid Services (cms.gov)
- SSA.gov — Social Security Administration, Medicare enrollment and premiums (ssa.gov)
- Medicare.gov — Find a SHIP (State Health Insurance Assistance Program) counselor
- HealthCare.gov — Affordable Care Act Marketplace enrollment information