The short answer: the Medicare Annual Enrollment Period runs October 15 through December 7 every year, and whatever you have on file when it closes takes effect January 1. It is your yearly chance to change Advantage plans, move between Advantage and Original Medicare, or change Part D drug coverage. It is not a window for switching Medicare Supplement plans, which trips up more people in South Carolina than anything else about the season.

Here is what the window actually covers.

What can you change during AEP?

Four things, and you do not need a reason or a qualifying event:

  • Original Medicare to Medicare Advantage.
  • Medicare Advantage back to Original Medicare, usually paired with picking up a Part D drug plan.
  • One Advantage plan to a different Advantage plan.
  • Join, switch, or drop a Part D drug plan.

Change your mind twice? The last election on file before December 7 is the one that takes effect. Nothing happens on the earlier ones.

What AEP does not cover

Medicare Supplement plans. This is the single biggest misunderstanding we deal with at our office in Sumter every fall, and it costs people real money when they assume otherwise.

Your one guaranteed shot at a Supplement is the Medigap Open Enrollment Period: 6 months, starting when you are both 65 and enrolled in Part B. During it, no health questions, no denials, no pricing you up for your history. It does not repeat.

South Carolina does not have a birthday rule, which is the annual do-over some other states created that lets you move to a comparable Supplement without underwriting. Here, once your 6 months pass, switching Supplements generally means answering health questions and getting approved, unless you fall into a specific guaranteed issue situation.

The practical version: the decision you make in your Medigap window is closer to permanent in South Carolina than it is in a birthday rule state. Our guide to Medicare Advantage versus Supplement covers the tradeoff, and it is worth reading before that window closes rather than after.

Why review your plan even if you like it?

Because the plan you liked this year is not automatically the plan you get next year.

By the end of September, your plan sends an Annual Notice of Change. It is the document nobody reads, and it is where the plan tells you exactly what is changing on January 1: costs, the drug list, the provider network, the extras. Any of those can move.

Three things worth checking every single year:

  • Your prescriptions, against next year’s drug list. Formularies change annually. A drug that was covered cheaply can move to a higher tier or come off entirely.
  • Your doctors and your hospital, against next year’s network. Networks change too, and finding out in February is worse than finding out in November.
  • What you actually spent this year. A plan with a low monthly cost is not cheap if you spent the year paying for it at the pharmacy counter.

Doing nothing is allowed. Just make it a decision rather than a default.

What about drug coverage?

Part D is where the yearly review pays for itself, because the drug list is the part most likely to change underneath you.

One structural change worth knowing: there is now an annual cap on what you pay out of pocket for covered drugs under Part D. It started in 2025 and the dollar figure is adjusted each year, so the useful thing to know is that the cap exists and that once you hit it, covered drugs cost you nothing for the rest of the year. Before that cap existed there was no ceiling at all.

If you skipped drug coverage when you were first eligible and did not have other creditable coverage, a late enrollment penalty of roughly 1 percent per month delayed can be added to your premium for as long as you have Part D. That one does not go away, which is covered further in when to enroll in Medicare.

What if you miss December 7?

If you are on a Medicare Advantage plan, you get a second window: the Medicare Advantage Open Enrollment Period, January 1 through March 31. It allows one change. You can move to a different Advantage plan, or drop back to Original Medicare and pick up a drug plan.

If you are on Original Medicare with a standalone drug plan, that window is not for you. Barring a Special Enrollment Period, which certain life changes open, your next opportunity is the following AEP.

How to use the window well

Start in October, not the first week of December. The plans are published in advance, the Annual Notice of Change is already in your hands, and the last week is when everyone calls at once.

Have three things ready: your prescription list with doses, your doctors and preferred hospital, and what you actually paid this year. Every useful comparison starts from those. A local Medicare agent can run them across the plans available in your county at no cost to you.

Frequently asked questions

When is the Medicare Annual Enrollment Period? October 15 through December 7 every year, with any change you make taking effect January 1. If you make more than one change during the window, the last one on file before December 7 is the one that counts.

What can I change during the Annual Enrollment Period? Four things: switch from Original Medicare to a Medicare Advantage plan, switch from Advantage back to Original Medicare, change from one Advantage plan to another, or join, switch, or drop a Part D drug plan. It is the one window each year that is open to everyone, with no qualifying event needed.

Can I switch my Medicare Supplement during AEP? This is the most common misunderstanding we see. AEP does not cover Medicare Supplement plans. Your one guaranteed window to buy a Supplement without health questions is the 6-month Medigap Open Enrollment Period that starts when you are 65 and enrolled in Part B. South Carolina does not have a birthday rule, so outside a guaranteed issue situation, switching Supplements here generally means answering health questions and being approved.

What if I like my plan and do not want to change anything? Read the Annual Notice of Change your plan sends before the end of September, then decide. Doing nothing is a real choice, but it is a choice to accept next year’s version of the plan, which can have a different drug list, different costs, or a different network than this year’s.

Is there another chance if I miss December 7? If you are on a Medicare Advantage plan, the Medicare Advantage Open Enrollment Period runs January 1 through March 31 and lets you make one change. If you are on Original Medicare with a drug plan, that window does not apply to you, and you generally wait for the next AEP unless you qualify for a Special Enrollment Period.

Griffin Insurance Agency is not connected with or endorsed by the United States government or the federal Medicare program. We do not offer every plan available in your area. Currently we represent 7 organizations which offer 48 products in your area. Please contact Medicare.gov or 1-800-MEDICARE to get information on all of your options.