You use the Medicare Part B enrollment form called CMS‑40B when you already have Part A and want to add Part B.

What the CMS‑40B form is

  • The official title is “Request for Enrollment in Medicare Part B (Medical Insurance)” , form CMS‑40B.
  • It is used if you already have Medicare Part A and now want to enroll in Part B, such as during your Initial Enrollment Period, the annual General Enrollment Period (Jan 1–Mar 31), or a Special Enrollment Period.

Where to get the Medicare Part B enrollment form

  • The current CMS‑40B form is available as a PDF directly from the Centers for Medicare & Medicaid Services (CMS); the file name typically looks like cms-40b-application-enrollment-medicare-part-b-medical-insurance.pdf.
  • You can also find it via the main Medicare forms page under Enrollment forms , where it links you to the Part B sign‑up forms.

How to submit the form

  • Once completed and signed, CMS‑40B is usually mailed or faxed to your local Social Security office , whose contact information you can locate using the Social Security Office Locator.
  • If you are enrolling using a Special Enrollment Period (for example, after employer coverage ends), you generally submit CMS‑40B together with form CMS‑L564 (Request for Employment Information) , which your employer fills out.

Key details you’ll need to complete CMS‑40B

  • Your Medicare Number , current mailing address, and phone number are required to complete the application.
  • If applying under a Special Enrollment Period, the instructions explain that CMS‑L564 from your employer must accompany CMS‑40B to document your group health plan coverage based on current employment.

Quick tips and next steps

  • Use the most recently dated version of CMS‑40B shown on the form (for example, CMS‑40B (07/2025)), so you know you are using the current format.
  • If you need help or accessible formats (large print, braille, or audio), CMS notes that you can contact 1‑800‑MEDICARE (1‑800‑633‑4227) or visit Medicare.gov’s accessibility and nondiscrimination page.

Information gathered from public forums or data available on the internet and portrayed here.