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Centers for Medicare & Medicaid Services

Fill out Form CMS-40B online

Request for Enrollment in Medicare Part B (Medical Insurance)

Form CMS-40B is how a person who already has Medicare Part A asks to sign up for Part B (Medical Insurance). It can be used during your Initial Enrollment Period, the General Enrollment Period (January 1–March 31 each year), or a Special Enrollment Period you qualify for. If you do not have Part A yet, this is not the right form: contact Social Security to apply for Medicare.

Fill out Form CMS-40BBlank form from the CMS

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Edition
(07/2025)
Pages
3
Fillable fields
47
Checked against the CMS
November 8, 2026

GuruPDF is not affiliated with the Centers for Medicare & Medicaid Services. This page explains the form in plain words; it is not legal or tax advice. Always check the official instructions before you file.

Who uses Form CMS-40B

  • People who have Medicare Part A and want to add Part B
  • People who delayed Part B because they had employer or union group health coverage
  • People who had health coverage as an international volunteer for a non-profit organization
  • People signing up for Part B during the General Enrollment Period

Before you start

  • Your Medicare Number
  • Your mailing address, phone number and email address
  • Start and end dates (month and year) of the job (yours or your spouse's) or volunteer work that gave you health coverage, and of that coverage
  • Form CMS-L564 filled out by your employer, if you had employer or union group health coverage
  • Proof or documents, if an employer, insurer or other entity asked or required you to enroll in Part B
  • The month and year you want coverage to start, if you are allowed to choose

How to fill out Form CMS-40B

  1. Section 1: Basic information

    Item 1 is your Medicare Number. Item 2 is your first, middle and last name and any suffix. Item 3 is your mailing address (street, P.O. Box or route, city, state and ZIP code). Items 4 and 5 are your phone number and email address. The form says all fields are required unless noted.

  2. Section 2, items 1 and 2: Group health and volunteer coverage

    Item 1 asks whether you have, or had, coverage through an employer or union group health plan since you turned 65. Item 2 asks whether you are, or were, an international volunteer for a non-profit organization that gave you health coverage. If you answer Yes to either one, complete item 3.

  3. Section 2, item 3: Dates of work and coverage

    Enter start and end dates as mm/yyyy for three things: when you (or your spouse) worked for an employer that provided health coverage, when you worked as a volunteer outside the U.S., and when the health coverage from the employer or non-profit ran. Check Not ended if it is still going. Attach a separate sheet if you need more space, and have your employer fill out Form CMS-L564 to send with your application.

  4. Section 2, item 4: Were you asked to enroll?

    Answer whether an employer, health insurance provider or other entity asked or required you to enroll in Part B. If you answer Yes, explain how and why in the space provided and include proof or documentation with the form.

  5. Choose your coverage start date

    This part applies if you are enrolling while still covered by a group health plan based on current employment, or during the first full month you are no longer enrolled in that plan. Choose one: the first day of the month you enroll, or the first day of one of the 3 months after you enroll. For the second choice, write the month and year as mm/yyyy.

  6. Section 3: Signature(s)

    Item 1 is the applicant's signature and item 2 is the date signed (mm/dd/yyyy). If the applicant signs with a mark (X), a witness who knows the applicant fills in items 3 to 5: the witness's first and last name, signature and date signed.

After you fill it out

Mail or fax the completed, signed form to your local Social Security office, or take it to the office in person. Find your office with the Social Security office locator on SSA.gov. Send Form CMS-L564 and any proof asked for in Section 2 with it. If you are signing up because employer group health coverage is ending, Social Security also offers its own online application on SSA.gov.

Signing: The applicant signs and dates Section 3. If the applicant signs with a mark (X), a witness who knows the applicant must also write their first and last name, sign and date; the form does not say whether an electronic signature is accepted, so follow Social Security's instructions.

Watch out for

  • Do not complete this form if you do not have Medicare Part A. Contact Social Security to apply for Medicare first.
  • The form notes that if you sign up for Part B, you must pay premiums for every month you have the coverage.
  • A Special Enrollment Period based on job coverage ends 8 months after the employment or the group health coverage ends, whichever happens first. COBRA is not group health plan coverage, and the end of COBRA or retiree coverage does not open a Special Enrollment Period.
  • If you sign up during the General Enrollment Period and do not qualify for a Special Enrollment Period, you might pay a monthly late enrollment penalty.

Questions about Form CMS-40B

Can I use Form CMS-40B if I do not have Medicare Part A?

No. The form says not to complete it if you do not have Part A. Contact Social Security to apply for Medicare for the first time.

When can I sign up for Part B with this form?

During your Initial Enrollment Period, during the General Enrollment Period from January 1 to March 31 each year, or during a Special Enrollment Period you qualify for. Medicare.gov lists the Special Enrollment Periods and when each one ends.

Do I also need Form CMS-L564?

If you had employer or union group health coverage since turning 65, the form asks you to have your employer fill out Form CMS-L564 (Request for Employment Information) and return it with your application. Social Security also says to fill it out when you apply during a Special Enrollment Period.

When will my Part B coverage start?

Coverage always starts on the first day of a month. In the General Enrollment Period it starts the month after you sign up. If you enroll while still covered by a group health plan from current employment, or in the first full month after it ends, you can choose the month you enroll or one of the 3 months after.

Where do I send the completed form?

Send it to your local Social Security office by mail or fax, or bring it in person. You can find the office with the locator on SSA.gov.

Official information

Page text last reviewed November 7, 2026.

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