Form CMS-40B - Request for Enrollment in Medicare Part B

What the form is

Form CMS-40B, Request for Enrollment in Medicare Part B, is how someone who already has Medicare Part A (hospital insurance) asks Social Security to add Part B (medical insurance, covering doctor visits, outpatient care and other services Part A does not). It is a short three-section form issued by the Centers for Medicare & Medicaid Services, part of the U.S. Department of Health and Human Services.

Who typically needs it

You use this form if you already have Part A and now want Part B, in one of three situations described on the form itself: during your Initial Enrollment Period around when you first qualify for Medicare, during the annual General Enrollment Period from January 1 to March 31, or during a Special Enrollment Period, most often after group health coverage through an employer or union ends. If you do not have Part A yet, this is not the right form. Contact Social Security directly to apply for Medicare for the first time.

What you need before you start

• Your Medicare number, exactly as printed on your Medicare card
• Your full legal name, mailing address, phone number and email
• Dates of any employer or union group health coverage since you turned 65, if applicable
• Dates of any international volunteer work for a non-profit that provided health coverage, if applicable
• A completed Form CMS-L564 from your employer if you are applying based on group coverage, since Social Security asks for it alongside CMS-40B
• A decision on your preferred Part B coverage start date, if you are still covered by a group health plan

How to fill it out online with PDF Editify

Click "Fill Template Now" to open the official CMS-40B in the editor with every field ready to type into. Work through it section by section, matching the numbers printed on the form.

Section 1: Basic information

Enter your Medicare number, full name (first, middle, last and suffix if any), mailing address, phone number and email address. This section has to match Social Security's records, so use your legal name as it appears on your Medicare card.

Section 2: Enrollment in Medicare Part B

Items 1 and 2 ask whether you have, or had, coverage through an employer or union group health plan since turning 65, or whether you were an international volunteer with non-profit health coverage. Answer yes or no to each. If you answer yes to either, complete item 3 with the start and end dates (or check "not ended") for your employment or volunteer work and for the related health coverage, using mm/yyyy format. Have your employer complete the companion Form CMS-L564 and submit it with this form. Item 4 asks if an employer, insurer or other entity required you to enroll in Part B. If yes, explain in the space provided and attach supporting documentation. Below that, choose your coverage start date if you are enrolling while still covered by a group plan: either the first day of the month you enroll, or the first day of one of the next three months, with the month and year you want written in.

Section 3: Signature

Sign and date the form. If someone signs by mark (an X) instead of a full signature, a witness who knows the applicant must also print their name, sign and date below it.

Signing and where to submit it

Add your signature in PDF Editify by drawing, typing or uploading an image, then download the completed PDF. Mail or fax the signed form to your local Social Security office. Use the office locator at SSA.gov/locator to find the correct mailing address or fax number for your area; CMS-40B does not list a single central mailing address because routing depends on where you live.

Deadlines and fees

There is no fee to submit CMS-40B itself. Once Part B starts, you pay a monthly premium, which the Medicare.gov costs page lists as $202.90 for 2026 as of October 3, 2026 for most people; higher-income beneficiaries pay more under the income-related adjustment. If you are applying under a Special Enrollment Period after group coverage ends, Social Security's rules generally give you an 8-month window to apply without a late-enrollment penalty, which is why people retiring in the fall often file this form in October, November or December. If you miss that window, you may have to wait for the next General Enrollment Period (January 1 to March 31) and could owe a permanent premium penalty, so check the current rules at Medicare.gov before you wait.

Common mistakes

• Leaving item 3's dates blank after answering yes to item 1 or 2, which stalls processing
• Forgetting to also send a completed CMS-L564 from the employer when enrolling based on group coverage
• Signing by mark without a witness signature next to it
• Missing the 8-month Special Enrollment window after employer coverage ends, which can trigger a late-enrollment premium penalty
• Sending the form to a generic CMS address instead of the local Social Security office found through SSA.gov/locator