Medicare Enrollment Periods Explained: When You Can Sign Up or Make Changes

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f Medicare's calendar feels confusing, you're not alone. There are several "windows," each with its own rules about what you can do and when coverage starts.

Once you know which window applies to you, decisions get much simpler. Here's a plain-English guide for 2026 and 2027 from our office in Oklahoma City.

It's October: 2027 Plans Are Here

Starting October 1 each year, Medicare Advantage and Part D drug plans may begin marketing next year's plans. That's why the Medicare mail and TV ads just picked up.

If you're already in a Medicare Advantage or drug plan, your plan was required to send you an Annual Notice of Change (ANOC) by September 30. It lists what's changing for 2027, like premiums, copays, and covered drugs. Please don't toss it. It's the best way to tell whether your plan still fits.

Initial Enrollment Period (Turning 65)

Your first chance to sign up is your Initial Enrollment Period. It lasts 7 months: the 3 months before the month you turn 65, your birthday month, and the 3 months after.

When your coverage starts depends on when you sign up:

• Premium-free Part A starts the month you turn 65.

• Part B: If you sign up before your birthday month, coverage starts the month you turn 65. If you sign up during your birthday month or the 3 months after, coverage starts the next month.

If you already get Social Security benefits, you're generally enrolled automatically. Otherwise, sign up through Social Security at SSA.gov or 1-800-772-1213.

General Enrollment Period (January 1 – March 31)

Missed your Initial Enrollment Period and don't qualify for a Special Enrollment Period? You can sign up for Part B (and premium Part A) during the General Enrollment Period, January 1 – March 31 each year.

Your coverage starts the first day of the month after you sign up. You may owe a late enrollment penalty (more on that below).

Medicare Open Enrollment (October 15 – December 7)

This is the big one most people hear about, often called the Annual Enrollment Period. From October 15 through December 7, you can:

• Switch from Original Medicare to a Medicare Advantage Plan, or back again

• Switch from one Medicare Advantage Plan to another

• Join, switch, or drop a Part D drug plan

Changes take effect January 1. This year, that means changes made by December 7, 2026 start January 1, 2027.

Medicare Advantage Open Enrollment (January 1 – March 31)

If you're already in a Medicare Advantage Plan, you get one more chance from January 1 to March 31. You can make one change: switch to a different Medicare Advantage Plan, or drop it and go back to Original Medicare (and join a separate drug plan).

Your change starts the first of the month after the plan gets your request.

Special Enrollment Periods (Life Changes)

Certain life events open a Special Enrollment Period outside the usual dates. Some common ones:

• Losing job-based coverage. If you delayed Part B because you (or your spouse) were still working with group health coverage, you have 8 months after the job or coverage ends (whichever comes first) to sign up for Part B without a penalty. You have 2 full months after that coverage ends to join a Medicare Advantage or drug plan.

• Moving. If you move out of your plan's service area, or move somewhere with new plan options, your chance to switch starts when you move and lasts 2 full months after. (If you tell your plan ahead of time, it can start the month before.)

• Medicaid (SoonerCare) or Extra Help. Since 2025, you can make a change once a calendar month: switch stand-alone drug plans, or leave a Medicare Advantage drug plan for Original Medicare plus a stand-alone drug plan. With full Medicaid, you can also join an integrated Dual Eligible Special Needs Plan monthly, where available. Changes start the next month.

• 5-star plans. If a plan rated 5 stars is available in your area, you can switch to it one time between December 8 and November 30 of the following year.

Medigap Open Enrollment, Plus Oklahoma's Birthday Rule

A Medicare Supplement (Medigap) policy helps pay costs Original Medicare doesn't. Your Medigap Open Enrollment Period is a one-time, 6-month window that starts the first month you're 65 or older and enrolled in Part B. During this time, companies can't turn you down or charge you more because of health problems.

Oklahoma adds another opportunity. Under an Oklahoma Insurance Department rule in effect since September 1, 2023 (often called the "Birthday Rule"), if you already have a Medigap policy, you get a 60-day window each year starting on your birthday. During that window you can switch to a policy with equal or lesser benefits, with the same company or a different one, without medical underwriting, as long as you haven't gone more than 90 days without Medigap coverage.

This rule applies only to Medicare Supplement policies, not Medicare Advantage.

Late Enrollment Penalties: The Basics

Penalties are added to your monthly premium and usually last as long as you have that coverage.

• Part B: an extra 10% for each full 12-month period you could have had Part B but didn't (unless you qualified for a Special Enrollment Period).

• Part D: an extra 1% for each full month you went without Part D or other creditable drug coverage, if the gap lasted 63 days or more in a row. The 1% is figured from the national base beneficiary premium: $38.99 in 2026 and $41.33 in 2027.

Medicare Enrollment Windows at a Glance

Enrollment Window	Dates	Coverage Starts
Initial Enrollment Period	7 months around your 65th birthday month	Birthday month, or month after you sign up
General Enrollment Period	Jan 1 – Mar 31	Month after you sign up
Medicare Open Enrollment	Oct 15 – Dec 7	January 1
Medicare Advantage Open Enrollment	Jan 1 – Mar 31 (one change)	Month after plan gets request
Special Enrollment Periods	Varies by life event	Usually month after request
5-Star Special Enrollment Period	Dec 8 – Nov 30 (once)	Month after request
Medigap Open Enrollment	6 months, starting when 65+ and in Part B	Set by the policy
Oklahoma Medigap Birthday Rule	60 days from your birthday, every year	Set by the policy

Frequently Asked Questions

When is Medicare Open Enrollment for 2027 coverage? October 15 through December 7, 2026. Any changes you make take effect January 1, 2027.

If I'm still working at 65, do I have to sign up for Part B? Not always. If you have group health coverage from your own or your spouse's current job, you may be able to delay Part B and sign up within 8 months after that job or coverage ends, penalty-free. COBRA and retiree coverage don't count.

Can I change my Medicare Advantage plan after January 1? Yes, if you're already in a Medicare Advantage Plan. From January 1 to March 31, you can make one change: switch to another Medicare Advantage Plan, or return to Original Medicare and add a drug plan.

What is Oklahoma's Medigap Birthday Rule? If you already have a Medicare Supplement policy in Oklahoma, you have 60 days each year, starting on your birthday, to switch to a policy with equal or lesser benefits without medical underwriting. It doesn't apply to Medicare Advantage plans.

What happens if I miss my Initial Enrollment Period? You can sign up during the General Enrollment Period (January 1 – March 31), and your coverage starts the month after you sign up. You may owe a Part B late enrollment penalty unless you qualify for a Special Enrollment Period.

Talk With a Local Medicare Agent

Medicare is easier to sort out when you can talk it through. Navigating Medicare is a local, independent agency at 2232 W. Hefner Road, Suite A, in Oklahoma City, helping folks across Shawnee, Oklahoma City, and nearby communities understand which window applies to them and what their options are.

Call us at 405-842-0494 or visit navigatingmedicare.com to set up a time to talk.

We do not offer every plan available in your area. Any information we provide is limited to those plans we do offer in your area. Please contact Medicare.gov or 1-800-MEDICARE to get information on all of your options.

Navigating Medicare is a local, independent agency. We are not connected with or endorsed by the U.S. government or the federal Medicare program.