Medicare Enrollment Timeline: Every Deadline and Penalty Explained

McIntosh Insurance Group doesn’t sell Medicare plans. This article is general information. For free, unbiased help with your Medicare choices in Florida, contact SHINE at 1-800-963-5337 or floridashine.org.

Medicare enrollment isn’t a single deadline. It’s a series of windows, and missing the first one can cost you for the rest of your life. Here’s every window in order.

Your Initial Enrollment Period

Your Initial Enrollment Period lasts seven months: the three months before the month you turn 65, your birthday month and the three months after.

Sign up before your birthday month and Part B coverage starts the first day of your birthday month.
Sign up during your birthday month or the three months after and coverage starts the first of the month after you sign up.
Premium-free Part A starts in your birthday month (or the month before, if your birthday falls on the 1st).

If you already get Social Security benefits, you’re usually enrolled in Parts A and B automatically.

If you’re still working at 65

If you or your spouse have health coverage from current employment, you may be able to delay Part B without a penalty. When that job or coverage ends, whichever happens first, you get an eight-month Special Enrollment Period to sign up for Part B.

COBRA and retiree coverage don’t count as coverage from current employment. Waiting until COBRA ends to sign up for Part B can mean a late penalty and a gap in coverage.

The General Enrollment Period

Missed your Initial Enrollment Period and don’t qualify for a Special Enrollment Period? You can sign up for Part B from January 1 to March 31 each year. Coverage starts the first of the month after you sign up, but you may owe a late enrollment penalty.

Medicare Open Enrollment: October 15 to December 7

Each fall you can switch between Original Medicare and Medicare Advantage, change Medicare Advantage plans, or join, switch or drop a Part D drug plan. Changes take effect January 1. The 2026 window, for 2027 coverage, is open now through December 7, 2026. CMS projects the average Medicare Advantage premium will fall from $14.37 a month in 2026 to $12.00 in 2027, and the Part D out-of-pocket cap will be $2,400 in 2027.

Medicare Advantage Open Enrollment: January 1 to March 31

If you’re already in a Medicare Advantage plan, you can make one change in this window: switch to another Medicare Advantage plan, or go back to Original Medicare and join a Part D plan. The change starts the first of the month after the plan gets your request. People new to Medicare Advantage get a similar chance during their first three months with Parts A and B.

Your Medigap Open Enrollment Period

You get a one-time, six-month window to buy a Medicare Supplement (Medigap) policy, starting the first month you have Part B and are 65 or older. During this window an insurer can’t turn you down or charge you more because of your health. After it ends, insurers can generally use medical underwriting unless you have a guaranteed-issue right.

Late enrollment penalties

Part	Penalty	How long
Part B	10% added to your premium for each full 12-month period you could have had Part B but didn’t	Generally for as long as you have Part B
Part D	1% of the national base premium ($38.99 in 2026) for each month without Part D or other creditable drug coverage, after a gap of 63 days or more	For as long as you have Part D

What Medicare costs in 2026

The standard Part B premium is $202.90 a month in 2026, the Part B deductible is $283 and the Part A hospital deductible is $1,736 per benefit period. CMS usually announces the next year’s amounts in the fall; the 2027 figures hadn’t been released when this article was published.

The timeline at a glance

Window	When	What you can do
Initial Enrollment Period	7 months around your 65th birthday	Sign up for Parts A and B, and a drug or Medicare Advantage plan
Special Enrollment Period	8 months after job-based coverage ends	Sign up for Part B without a penalty
General Enrollment Period	January 1 – March 31	Sign up for Part B if you missed your window
Medicare Open Enrollment	October 15 – December 7	Change Medicare Advantage or Part D plans
Medicare Advantage Open Enrollment	January 1 – March 31	One change if you’re in Medicare Advantage
Medigap Open Enrollment	6 months from your Part B start at 65+	Buy any Medigap policy without health questions

Free help in Florida

SHINE (Serving Health Insurance Needs of Elders), run by the Florida Department of Elder Affairs, offers free, unbiased and confidential Medicare counseling. Call 1-800-96-ELDER (1-800-963-5337) or visit floridashine.org. Outside Florida, search for your state’s SHIP program.

Still working past 65, or helping a younger family member with coverage? We can help with the under-65 side of the household.

Sources

Medicare.gov, When does Medicare coverage start?: https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start
Medicare.gov, Joining a plan: https://www.medicare.gov/basics/get-started-with-medicare/get-more-coverage/joining-a-plan
Medicare.gov, Avoid late enrollment penalties: https://www.medicare.gov/basics/costs/medicare-costs/avoid-penalties
Medicare.gov, Medigap: ready to buy: https://www.medicare.gov/health-drug-plans/medigap/ready-to-buy
CMS, Understanding Medicare Advantage and drug plan enrollment periods: https://www.medicare.gov/publications/11219-Understanding-Medicare-Advantage-Medicare-Drug-Plan-Enrollment-Periods.pdf
CMS, Medicare & You 2027: https://www.medicare.gov/publications/10050-medicare-and-you.pdf
CMS, 2026 Medicare Parts A and B premiums and deductibles: https://www.cms.gov/newsroom/fact-sheets/2026-medicare-parts-b-premiums-deductibles
CMS press release, September 28, 2026, on 2027 Medicare Advantage and Part D: https://www.cms.gov/newsroom/press-releases/medicare-advantage-medicare-prescription-drug-programs-expected-remain-stable-2027
Florida SHINE: https://www.floridashine.org/

The Medicare Enrollment Timeline: Every Deadline You Need