Quick Summary: Medicare’s Annual Enrollment Period runs October 15 through December 7, and your plan may well have changed since last year. The mistakes that cost people the most are tossing the Annual Notice of Change without reading it, not rechecking prescriptions and doctors, choosing on the monthly premium alone, and missing the December 7 deadline. 20 minutes of review now can save you money and a lot of frustration in January.
Every fall, Medicare gives you a window to change your coverage for the coming year. For 2026, that window runs October 15 through December 7, and anything you change takes effect January 1, 2027.
And honestly? We get why most people treat it like a renewal notice. The mail pile in October is overwhelming. The language is dense. And it’s tempting to glance at the premium and let the plan roll over.
But then January comes. And the prescription that costs $15 is now $90. Or the specialist you’ve seen for years is suddenly out of network.
Premiums move, and so do drug lists and doctor networks. What worked in 2026 might not work in 2027. Here are the five most common mistakes we see every enrollment season.
1. Tossing the Annual Notice of Change without reading it
Your plan has to send you an Annual Notice of Change by September 30. It’s not junk mail. It’s the one document that spells out what’s changing with your costs and coverage next year.
Most people never open it. We understand why — it looks like every other piece of insurance mail. But the surprises show up in January, when it’s too late to do anything about them.
So when that envelope shows up, open it. Skim for anything marked as a change or an increase. If something looks different, that’s your cue to compare plans before December 7.
2. Not checking your prescriptions
Drug lists change every year. A medication that’s been $15 all year can jump to a higher tier. Or fall off the list entirely. If you take even one regular prescription, this is the mistake most likely to hit your wallet.
Write down every prescription you take, with the dose. Then check it against your plan’s drug coverage for next year. Medicare’s plan finder at medicare.gov lets you enter your drugs and compare real costs across plans. 20 minutes here can save you hundreds of dollars.
3. Assuming your doctors are still in the network
Provider networks shift more than people realize. A hospital system and an insurer have a contract dispute, and suddenly your cardiologist is out of network. You don’t find out until you’re sitting in the waiting room.
Check the provider directory for the plan year you’re shopping for. Directories update every fall, so last year’s version won’t tell you what you need to know. Pay special attention to your specialists and the hospital you’d go to. When in doubt, call the plan and ask.
4. Choosing on the monthly premium alone
A $0-premium plan feels like a win. Until you look at the rest of the math. The premium is only part of it — deductibles and copays are where the costs can add up. If you use your coverage, a plan with a modest premium and a low out-of-pocket max can cost you far less over the year than the “free” one.
Think in total yearly cost, not monthly premium. Add up 12 months of premiums, then add what you’d pay for your typical visits and prescriptions. The cheapest premium is rarely the cheapest plan.
5. Missing the December 7 deadline
After December 7, you’re generally locked in until next fall. There are exceptions. If you’re in a Medicare Advantage plan, you get another window from January through March. And certain life events trigger special enrollment periods. But don’t count on those.
Put December 7 on the calendar now. Better yet, aim to decide by Thanksgiving. The last week of enrollment is typically the busiest time for every advisor and call center in the country.
One more thing worth knowing. The Annual Enrollment Period works differently for Medicare Supplement (Medigap) plans. If you’re thinking about moving from Medicare Advantage to Original Medicare plus a Supplement, talk to an advisor first. In most cases you’ll go through medical underwriting. Have that conversation before you make any moves.
A simple way to do your review
You don’t need a spreadsheet. Just do these four things:
- Open the Annual Notice of Change when it arrives.
- Write down your prescriptions (with doses) and your doctors.
- Compare your total yearly cost across two or three plans, not just the premium.
- Talk to someone you trust before December 7.
Talk it through with an advisor
Nobody should have to sort this out alone, staring at fine print at the kitchen table. At Walsh, our expert Medicare advisors do this every fall, and they can sit down with you and go through your plan piece by piece. Bring your list of prescriptions and the names of your doctors, and we’ll help you weigh your options and decide what makes sense for next year.
Frequently asked questions
Q: When is Medicare open enrollment?
A: The Annual Enrollment Period runs October 15 through December 7 every year. Changes you make during that window take effect January 1 of the following year.
Q: What happens if I do nothing during enrollment?
A: Your current plan renews automatically, including any changes it made for the new year. Doing nothing is a choice. Just make it an informed one.
Q: Can I switch from Medicare Advantage back to Original Medicare?
A: Yes, during the Annual Enrollment Period. But if you want to add a Medicare Supplement plan, you’ll typically go through medical underwriting. Talk to an advisor before you switch.
Q: Does the Annual Enrollment Period apply to Medigap plans?
A: Not in the same way. Medigap has its own enrollment rules, and the fall window doesn’t give you a guaranteed right to switch Supplement plans. This is one of the most misunderstood parts of Medicare, so ask us to be sure.
Q: What if I miss the December 7 deadline?
A: Your options get narrow. If you’re in a Medicare Advantage plan, you can make one change during the Medicare Advantage Open Enrollment Period, January 1 through March 31. Certain life events, like moving or losing other coverage, can trigger a Special Enrollment Period. Otherwise, you’re waiting until next fall.