Enrollment Timeline
IEP, GEP, SEP, AEP, MA OEP — decoded.
IEP — Initial Enrollment Period
The 7 months around your 65th birthday. This is when most people first enroll in Parts A and B. Missing it can trigger lifetime Part B penalties unless a Special Enrollment Period applies.
GEP — General Enrollment Period
January 1 – March 31 every year. If you missed your IEP and don't qualify for a Special Enrollment Period, this is when you can sign up for Parts A and B. Coverage starts the month after you enroll.
SEP — Special Enrollment Period
Triggered by qualifying life events: losing employer coverage (8 months for Parts A and B), moving out of your plan's service area, losing Medicaid or Extra Help, and others. Each SEP has its own start date, length, and rules.
AEP — Annual Enrollment Period
October 15 – December 7 every year. This is when you can join, switch, or drop a Medicare Advantage plan, and when you can switch Part D plans. Changes take effect January 1.
MA OEP — Medicare Advantage Open Enrollment
January 1 – March 31 every year, only for people already in a Medicare Advantage plan. You can switch to a different Advantage plan or drop back to Original Medicare (and add a Part D plan). You can make one change during this window.
Medigap Open Enrollment
A one-time 6-month period that starts when you're 65 and enrolled in Part B. During this window, Medigap insurers can't turn you down or charge more based on health. After it ends, most states allow underwriting.