Glossary
Initial Enrollment Period (IEP)
The 7-month window around your 65th birthday when you first sign up for Medicare without penalty.
Also known as: IEP, Initial Enrollment
What is it?
Your Initial Enrollment Period is a 7-month window: the 3 months before, the month of, and the 3 months after your 65th birthday. It's your first chance to enroll in Medicare Parts A and B.
Why does it matter?
Enroll in the first 3 months and coverage starts the month you turn 65 — preventing any gap between TRICARE Prime/Select and TFL. Enroll later in the window and coverage is delayed, creating a TFL gap.
When you'll encounter it
Exactly once, around your 65th birthday. Mark your calendar 90 days before.
Impact on Medicare
Defines when your Medicare A and B will begin and avoids any late-enrollment penalty.
Impact on TRICARE For Life
Critical. TFL activates the day Medicare A and B both become effective. Missing your IEP window means losing TFL too — and TRICARE does not qualify for a Special Enrollment Period.
Common misconceptions
- "I can sign up anytime." — Outside of IEP you can only sign up during the General Enrollment Period (Jan 1 – Mar 31, with coverage starting the following month) — and you'll owe late penalties.
Related lessons
Related glossary terms
Related questions
Official sources
Last reviewed January 2026 against the 2026 Medicare & You and TRICARE For Life handbooks.