Medicare Initial Enrollment Period — 2027

Your Initial Enrollment Period is personal: it is tied to your 65th birthday, not to a calendar season. Use the calculator on this page to see your exact dates.

Your Initial Enrollment Period starts three months before the month you turn 65 and ends three months after it: seven months in total. If your birthday falls on the 1st of a month, Medicare treats you as turning 65 in the month before, and the whole window shifts one month earlier.

Signing up in the three months before your birthday month makes Part B start the month you turn 65. Signing up later can delay your Part B start date, and waiting past the window without qualifying employer coverage adds a late-enrollment penalty of 10% of the Part B premium for each full 12-month period you were eligible but not enrolled, for as long as you have Part B.

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See also the turning 65 checklist and the full eligibility calculator.

Frequently asked questions

When exactly is my Initial Enrollment Period?

It runs from three months before the month you turn 65 through three months after that month. If your birthday is on the 1st, the window starts one month earlier.

What happens if I sign up late for Part B?

Without qualifying employer coverage, the Part B premium carries a 10% late-enrollment penalty for each full 12-month period you were eligible but not enrolled, and the penalty lasts as long as you have Part B.

Researched and reviewed by Jordan Diaz, Licensed Insurance Agent, NPN 18910035, Senior Benefit Assistance. This page does not display plan data; the plan figures elsewhere in this section come from CMS’s published CY2027 Landscape Source File, data as of October 18, 2026. Last reviewed: October 26, 2026.