Medicare Initial Enrollment Period Explained: The 7-Month Window
Direct answer: The Medicare Initial Enrollment Period (IEP) generally spans seven months: the three months before your 65th birthday month, your birthday month itself, and the three months after.
Why timing inside the window matters
Enrolling in the three months before your birthday month typically means coverage starts the month you turn 65. Waiting until later in the window can delay your effective date by one to three months, which matters if you have a procedure or prescription need lined up.
The cost of missing the IEP entirely
Missing the full window without qualifying employer coverage can trigger a late enrollment penalty for Part B that's added to your premium for as long as you have Medicare — a cost that compounds for the rest of your life, not just a one-time fee.
Medigap's separate clock
Once Part B starts, a separate Medigap open enrollment period generally runs for six months, during which insurers typically can't deny you a policy or charge more based on health history. Missing that window can mean medical underwriting on any Medigap policy you apply for later.
Do I need to enroll if I still have employer coverage?
Not always — if your employer coverage is considered creditable and your employer has enough employees, you may qualify for a Special Enrollment Period instead, avoiding the penalty. Confirm this with your HR department before your 65th birthday.