Medicare·8 min read

Medicare Enrollment Periods Explained (IEP, AEP, OEP, SEP)

The acronyms are confusing, but missing the right window can cost you thousands. Here's a plain-English guide to every Medicare enrollment period.

Key Takeaways

1
Initial Enrollment Period (IEP): 7 months around your 65th birthday — don't miss it.
2
Annual Election Period (AEP): Oct 15 – Dec 7 every year for plan changes.
3
Open Enrollment Period (OEP): Jan 1 – Mar 31 to switch Medicare Advantage plans.
4
Special Enrollment Periods (SEP): triggered by life events like moving or losing employer coverage.

Initial Enrollment Period (IEP)

Your IEP is a 7-month window: the 3 months before your 65th birthday, your birthday month, and the 3 months after. This is when you enroll in Original Medicare (Parts A and B).

Missing IEP can trigger a lifetime late enrollment penalty for Part B (10% per year) and Part D (1% per month). These penalties never go away.

Annual Election Period (AEP)

Every year from October 15 through December 7, you can switch Medicare Advantage plans, switch from Original Medicare to Advantage (or vice versa), or change your Part D drug plan.

Changes take effect January 1. This is the only time most people can make these changes — outside of qualifying events.

Open Enrollment Period (OEP)

From January 1 through March 31, Medicare Advantage enrollees get one chance to switch to a different Advantage plan or back to Original Medicare with a Part D plan.

OEP is a one-time-per-year do-over for Advantage enrollees who picked the wrong plan during AEP.

Special Enrollment Periods (SEP)

SEPs are triggered by qualifying events: moving to a new ZIP code, losing employer coverage, qualifying for Medicaid, or your plan leaving the market.

Each SEP has its own rules and timeline (typically 60 days from the event). We help clients spot SEPs they didn't realize they qualified for.

Source: Medicare.gov — Enrollment Periods ↗

Medicare