Medicare 101 · 04

Enrollment periods.

Medicare has four main enrollment windows. Your Initial Enrollment Period is the 7-month window around your 65th birthday. The Annual Enrollment Period runs October 15 to December 7 every year for changing Medicare Advantage or Part D plans. Special Enrollment Periods are triggered by life events like losing employer coverage. The General Enrollment Period (January 1 to March 31) is a fallback that may carry late-enrollment penalties. Missing the wrong one can mean lifetime penalties.

Initial Enrollment Period (IEP) — 7 months

The first window for everyone turning 65. Starts 3 months before your birthday month and ends 3 months after. If you sign up before your birthday month, coverage starts on the 1st of your birthday month. If you sign up the month of or after, there's a 1-month delay.



For people becoming eligible through disability, IEP runs 3 months before through 3 months after the 25th month of SSDI.

General Enrollment Period (GEP) — Jan 1 to Mar 31

If you missed your IEP and don't qualify for a Special Enrollment Period, this is your fallback. Coverage starts the month after you enroll. You'll likely owe the Part B late penalty—10% of the premium for every full 12 months you delayed, for life.

Special Enrollment Period (SEP) — varies

An 8-month window triggered by a qualifying event—most commonly losing employer coverage. Other triggers: moving out of your plan's service area, your plan ending its contract with Medicare, becoming eligible for Medicaid, etc.

If you delayed Part B because you had active employer coverage from a job with 20+ employees, you generally have an SEP and don't owe the penalty—provided you enroll within the window.

Annual Election Period (AEP) — Oct 15 to Dec 7

Once a year, every Medicare beneficiary can:

• Switch from Original Medicare to a Medicare Advantage plan (or vice versa)
• Switch from one MA plan to another
• Join, drop, or change a Part D plan



Changes take effect January 1. This is also the window we use for our annual client review—plans change every year, and we want to make sure yours still fits.

Medicare Advantage Open Enrollment Period — Jan 1 to Mar 31

If you're already in an MA plan, you get one chance to either switch to a different MA plan or drop MA entirely and return to Original Medicare. New coverage starts the 1st of the month after your change.

The other big window — California Medigap Birthday Rule

California is one of a handful of states with a guaranteed-issue Medigap window every year—60 days starting on your birthday. Full details on the CA Birthday Rule →

Penalties summary

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