Official forms The IRIS mailing library
How to file Social Security Form CMS-40B for Medicare Part B
Use the current CMS-40B to request Medicare Part B, complete its three sections, and submit the signed form to your local SSA office by mail or fax.
At a glance
Use the current CMS-40B for Part B enrollment
CMS-40B is the Request for Enrollment in Medicare Part B (Medical Insurance). The current revision is 07/2025. CMS says to use it if you already have Medicare Part A and want to sign up for Part B during an Initial Enrollment Period, General Enrollment Period, or an applicable Special Enrollment Period.
If you do not have Part A, the form directs you to contact Social Security to apply for Medicare for the first time rather than using CMS-40B.
Complete the three sections
Section 1: Basic information.
Enter the Medicare Number, name, mailing address, phone number, and email address requested on the form. The form marks all fields as required unless noted.
Section 2: Enrollment in Medicare Part B.
Answer the employer or union group health plan and international volunteer questions. If instructed, enter the employment and coverage dates, provide any requested explanation or documentation, and choose a coverage start date from the options available on the form.
Section 3: Signature.
Sign and date the application. If the applicant signs by mark, a witness who knows the applicant must also complete the witness fields.
Submit it to Social Security.
Mail or fax the completed, signed form to your local Social Security office. Use the SSA office locator for the current destination.
When CMS-L564 accompanies the application
Section 2 of CMS-40B asks about employer or union group health plan coverage and directs applicants completing the employment and coverage dates to have the employer fill out CMS-L564. The current CMS-L564 instructions say to submit it with CMS-40B to the local Social Security office by mail or fax.
Follow the instructions on the current forms for your circumstances. Social Security decides eligibility, enrollment timing, and whether it needs additional information.
Privacy boundary for IRIS
CMS-40B requires a Medicare Number, which is a government identifier. Without an applicable written agreement with IRIS, do not submit a form containing a government identifier or highly sensitive medical record through IRIS. Send this form directly to Social Security by an accepted method instead.
Sources and current instructions
Review the linked source when a mailing depends on current USPS, agency, contractual, or legal requirements.
Use the current official CMS-40B.
Download the 07/2025 form from CMS, then submit it directly to your local Social Security office by mail or fax.
Form CMS-L564: Employer verification for Medicare Part B
Complete CMS-L564 for a Medicare Special Enrollment Period. The applicant fills Section A, the employer fills Section B, and both forms go to SSA.
Read the guide
How to prepare and mail official paper forms
Prepare official forms for mailing by checking the issuer's current signature, attachment, address, deadline, and submission instructions before sending.
Read the guide
CMS-408 is not a current Medicare form
There is no current Medicare form CMS-408. Choose CMS-40B to enroll, CMS-L564 for employment information, or CMS-1763 to end coverage through SSA.
Read the guidePlanning mail for a business or team?
Tell us the mailpiece type, expected volume, and workflow you need. We will confirm whether the current IRIS letter, form, or postcard service fits.