The five Medicare deadlines that actually matter

If you take one thing from this article: the only deadline that can permanently raise what you pay is the one around your 65th birthday. The rest are recoverable. Here they are in the order they’ll matter to you.

1. Your Initial Enrollment Period — seven months around your 65th birthday

It opens three months before the month you turn 65, includes your birthday month, and closes three months after. Enroll in Part A and Part B in this window and there’s no penalty and no gap. Sign up in the three months before your birthday month and coverage starts the first day of your birthday month.

The exception that trips people up: if you’re still working and covered by a qualifying employer group health plan, you may be able to delay Part B safely. Whether that’s true depends on how many employees the company has and how the plan is structured — confirm it before your birthday, not after.

2. Your six-month Medigap open enrollment

This is the most valuable window in Medicare, and almost nobody mentions it. For six months starting when your Part B takes effect, you can buy any Medicare Supplement policy sold in your state with no health questions asked. After it closes, most states let insurers underwrite — meaning they can charge more or decline you.

3. Annual Enrollment — October 15 to December 7

Every year, this is your dependable chance to change Medicare Advantage or Part D plans. Whatever you choose takes effect January 1. It’s also the right moment to re-price your prescriptions, because formularies change every January — a plan that was cheapest last year often isn’t.

Miss it and you generally keep what you have for another year, unless you qualify for a Special Enrollment Period. Inconvenient, not permanent.

4. Medicare Advantage Open Enrollment — January 1 to March 31

If you’re already in a Medicare Advantage plan and January makes it obvious the plan doesn’t fit, you get one change during these three months: switch to another Advantage plan or return to Original Medicare. One change, not several.

A caution: returning to Original Medicare doesn’t guarantee you can buy a Medigap policy. Outside a guaranteed-issue right, that purchase may require underwriting.

5. The 63-day drug coverage rule

Go 63 days or more without Part D or other creditable prescription coverage after you’re eligible, and a late enrollment penalty is added to your Part D premium — roughly 1% of the national base premium for every month you went without, for as long as you have Part D coverage.

This is why people who take no medications still buy a minimum-premium plan. It’s inexpensive insurance against both a new prescription and a permanent surcharge. Coverage through the VA, TRICARE, or a retiree plan usually counts as creditable — but get that in writing.

What about all the other deadlines you’re hearing about?

If a postcard or a phone call is pressuring you toward a date that isn’t one of the five above, treat it as marketing. Real Medicare deadlines are published by CMS and don’t depend on calling a particular number today.

Special Enrollment Periods are the genuine exception to all of this. Losing employer coverage, moving to a new service area, gaining Medicaid or Extra Help, or a plan leaving your county can each open a window outside the normal calendar. If your life changed, ask — you may have more options than you think.

This article is general information, not advice about your specific situation, and figures reflect the 2026 plan year. For official information, see Medicare.gov’s enrollment pages or call 1-800-MEDICARE.