Every Medicare Deadline That Matters — and What Missing One Costs

Reviewed by Virginia Barausky, CLTC, RSSA® · August 10, 2026 · figures verified against CMS.gov / SSA.gov

When is my Initial Enrollment Period (IEP)?

Your IEP is the 7-month window wrapped around your 65th birthday: the 3 months before your birthday month, your birthday month, and the 3 months after. Enrolling in the first 3 months means coverage starts the month you turn 65.

What is the Annual Enrollment Period (AEP)?

October 15 – December 7 every year. This is when anyone on Medicare can switch Advantage plans, move between Original Medicare and Advantage, or change Part D drug plans, with changes effective January 1. Because plan networks, formularies and premiums change every year, an annual review is not optional busywork — it's how you avoid paying next year for a plan that fit last year.

What is the Medicare Advantage Open Enrollment Period (OEP)?

January 1 – March 31. If you're already in a Medicare Advantage plan, you get one switch — to another Advantage plan or back to Original Medicare (plus a Part D plan) — during this window.

What is a Special Enrollment Period (SEP)?

Life events open extra windows: leaving employer coverage after 65, moving out of your plan's service area, plan terminations, and certain other qualifying events. SEPs are the reason working past 65 without penalties is possible — if the paperwork is timed correctly.

What happens if I miss my window?

The Part B late-enrollment penalty adds 10% to your premium for every full 12-month period you delay without creditable coverage — and it lasts for as long as you have Part B (source: Medicare.gov). On the 2026 standard premium of $202.90, a two-year delay means roughly $40.58 more per month, every month, for life. Run your own numbers with our Part B penalty calculator.

Frequently asked questions

I'm still working at 65. Do I have to enroll?

If you have creditable employer coverage (generally from an employer with 20+ employees), you can usually delay Part B without penalty and enroll later through a Special Enrollment Period. The definition of 'creditable' is where mistakes happen — verify before you delay.

When does coverage start if I enroll during AEP?

January 1 of the following year.

Can I switch Medigap plans anytime?

You can apply anytime, but outside your 6-month Medigap open enrollment window (which starts when you're 65+ and enrolled in Part B), most states — including Florida — allow medical underwriting, meaning approval isn't guaranteed.