Turning 65 · Utah

Turning 65 During Open Enrollment: When Does My Plan Start?

If your 65th birthday falls between November and March, two Medicare windows are open for you at once. They point to different start dates, and in one case a different plan year. Here is the date each birthday month gets, and the choice a November or December birthday has to make.

Medicare On Main Data Desk

Published October 18, 2026 · 8 min read · Reviewed by Brian Penner

Every fall a few people call us with the same worry. Their 65th birthday is in December or February, the TV ads keep saying the December 7 deadline, and they're afraid they'll miss Medicare. They won't. Open Enrollment is for people who already have Medicare and want to change plans. A 64-year-old has a separate window, and it was open before the ads began. But the two windows do overlap for anyone whose birthday falls from November through March, and when they overlap, the start date isn't always what you'd guess. Below are the actual rules, from the guidance CMS gives the plans.

Two windows, two different jobs

Your Initial Enrollment Period "lasts for 7 months, starting 3 months before you turn 65, and ending 3 months after the month you turn 65" (Medicare.gov). It's the window for Part A and Part B. For a Medicare Advantage plan, CMS uses a matching window called the Initial Coverage Election Period, and stand-alone drug plans have the same seven months. That window "always begins three months prior to the date an individual has both Medicare Part A and Part B for the first time" (CMS § 30.2).

Open Enrollment runs October 15 – December 7, and "the changes you make during Open Enrollment are effective January 1 of next year" (Medicare.gov). It's for switching Medicare Advantage and Part D plans. It never adds Part A or Part B.

The overlap matters because each window has its own start-date rule. Under the initial window, a plan you choose before your Medicare begins "is effective as of the first day of the month in which the individual is entitled to both Part A and Part B." If you choose after that, it starts the first of the next month. Under Open Enrollment, the start date is January 1. When you qualify for both, CMS tells the plan that it "must allow the individual to choose the enrollment effective date from those available under the applicable election periods" (§ 30.7). There's one limit: you "may not choose an effective date any earlier than the month of entitlement to Medicare Part A and Part B."

Your start date, by birthday month

Computed from CMS's CY2027 enrollment guidance §§ 30.2 and 30.7, Medicare.gov's start-date rules and the Medigap 6-month window. This assumes you signed up for Parts A and B in the three months before your birthday month. "If your birthday is on the first of the month, coverage starts the month before you turn 65," so move every date one month earlier. Signing up in your birthday month or later pushes Part B to the month after you apply. For the full list of dates, see when Medicare coverage starts.

February and March: Open Enrollment can't move your start date up

This is the case people get wrong most often, so CMS spells it out. "An individual is entitled to Medicare Part A and Part B in February. Their ICEP is the seven-month period from November through May. If the plan receives an enrollment request from that individual during the AEP (October 15–December 7), the individual may not choose a January 1 effective date. The individual must be given a February 1 effective date for the ICEP because January 1 is earlier than the month of entitlement to Medicare Part A and Part B" (CMS § 30.7). A separate drug plan follows the same rule.

In practice, whatever covers you now, whether it's an employer plan, COBRA, a Utah Marketplace plan or a spouse's plan, has to carry you through January 31. If you have Marketplace coverage, set its end date to match. The Marketplace post explains the end-date rules. For a March birthday, Open Enrollment does almost nothing for you. Your plan window opens December 1, so a choice made December 1 through 7 counts, and coverage starts March 1. Choosing in January or February works just as well.

November and December: a 2026 plan for a month or two, or wait for 2027?

This is where you have a real choice. If Part A and B start December 1, a plan you join before then can start December 1. But in December the only version of any plan is the 2026 version. Because you are also inside Open Enrollment, you can choose a 2027 plan with a January 1 start instead. Before the first plan starts, you can change your mind. CMS: "The last enrollment choice made, determined by plan receipt date, will be the choice that becomes effective" (§ 20). Three things to weigh:

• The deductible and limits restart on January 1. A Part D plan has a calendar-year deductible, up to $615 in 2026 and $700 in 2027 under the standard benefit, and an out-of-pocket cap of $2,100 in 2026 and $2,400 in 2027. A Medicare Advantage plan's yearly maximum restarts too. If you have a big drug bill or surgery in December, it counts toward 2026 totals that reset a few weeks later.
• The plan you join for December may change or end in January. Members got the Annual Notice of Change for 2027 by September 30, before you joined, so ask the plan for it. In Utah, HealthSpring Premier (HMO-POS) and HealthSpring True Choice (PPO) have 2026 versions but none for 2027. A December start in either one, if the plan accepts you, would end December 31. Salt Lake County drops from 24 Medicare Advantage plans with drug coverage to 22. The HealthSpring post and the 2027 Salt Lake list have the details.
• Skipping drug coverage for a month isn't free. Medicare.gov's two rules for avoiding the Part D penalty are to "get Medicare drug coverage when you first get Medicare Part A and/or Part B" and not to "go 63 days or more without creditable drug coverage" (Medicare.gov). If you think about leaving November or December without drug coverage, talk to us first.

For many people, the simplest fit is a 2026 plan for the first month or two, then a 2027 choice made in the same Open Enrollment so the switch is set for January 1. Others with Original Medicare plus a Medigap policy take a stand-alone 2026 drug plan for December and change it for 2027. What doesn't work is choosing your 2026 plan in October and assuming it carries into 2027 unchanged. If you make no second choice, the plan does carry into its 2027 version, if it has one, with whatever changes that version brings.

Medigap runs on its own clock

None of the dates above apply to a Medicare Supplement. Your Medigap Open Enrollment is six months long and starts the first month you have Part B and are 65 or older (Medicare.gov). A December 1 Part B start gives you December 1 through May 31. During those months no insurer can turn you down or charge more because of your health. A fall birthday changes only one thing here: Medigap rates change on each company's own schedule, so a policy that starts in December could see a rate change soon after. Ask the company when its next one is due. The Medigap window post explains what Utah law adds.

After your plan starts, you still have options

Choosing in a hurry this fall doesn't lock you in. "Once an election takes effect, eligibility for that election period ends" (CMS § 20), but other windows open after it. Open Enrollment itself, if it's still open. The Medicare Advantage Open Enrollment Period from January 1 to March 31. A separate change window in your first three months of Medicare, which we cover in its own post. Before using any of them, read the plan's documents. The Annual Notice of Change explainer shows what to look for.

What I would do this week

1. Find your Part B start date. It's on your Social Security approval or your Medicare card. If you haven't applied yet and your birthday is in November or later, apply now so you get the first-of-the-month start.
2. Look up your row in the table. Figure out whether you are choosing a 2026 plan, a 2027 plan, or both.
3. Set your current coverage's end date to the day before your plan starts, never the day before January 1 by default.
4. For a November or December start, compare the plan's 2026 and 2027 versions. Check doctors, drugs and the yearly maximum, and confirm the plan has a 2027 version at all.
5. Mark your Medigap window if you're considering a supplement. It's the six months that start with Part B.
6. Check every plan in your county on the Medicare Plan Finder, and use our Turning-65 page for the rest of the checklist.

Where these facts come from: the Medicare On Main Data Desk builds each article from public records. This one uses CMS's CY2027 Medicare Advantage and Part D enrollment guidance, especially the election-period, overlap and effective-date sections. It also uses Medicare.gov's pages on coverage start dates, Open Enrollment, Part D penalties and Medigap timing, CMS's 2027 Part D parameters, and the CMS 2026 and 2027 plan landscape files for Utah. The month-by-month windows are our arithmetic on CMS's definitions. Social Security handles Part A and B enrollment, and the plans process plan elections under CMS rules. Confirm your own dates with Social Security, Medicare.gov or a licensed agent. No carrier pays us to feature a plan.