Social Security Administration · Medicare

Medicare Part B Enrollment Application (Form CMS-40B)

Add Part B to the Part A you already have — in the right window, without the penalty surprises.

Form CMS-40B is the paper way to add Medicare Part B (medical insurance) when you already have Part A. The form itself is one page — the real questions are which sign-up window you're in, whether the late penalty applies, and what proof to attach. This walkthrough sorts your window first, then fills the form with you.

Start the walkthrough View the official source

Average time

10–15 minutes

Difficulty

straightforward — the window decision is the only hard part

Best for

People with Part A whose job coverage is ending, or who are using the January–March General Enrollment Period.

What this form stands for

Enroll in Part B inside a valid window with the right attachments, so coverage starts on time and no avoidable late penalty is added.

The form's printed instructions are decades old: they still say General Enrollment coverage starts July 1 and never mention the 3-month delayed-start option. Current Medicare rules — coverage the month after sign-up — are what SSA applies, and what this walkthrough follows.

What you'll need

Your Medicare card (for your claim number)
Your mailing address and phone number
Job-coverage window: form CMS-L564 and your employer coverage end month
Mark (X) signature: a witness who knows you, plus their address

How the walkthrough is organized

Your sign-up window

Right-form check, then the window that decides your start date, penalty, and attachments.

About you

Claim number, name, whose record, address, and phone.

Sign and date

Written signature or mark (X) — and the witness block only if you need it.

Send it in

Print, sign in ink, attach CMS-L564 if required, and get it to your Social Security office.

Ready to start?

Docgle asks calm, plain-English questions and keeps the official source attached for review.

Start cms-40b-medicare-part-b-enrollment walkthrough