The CMS-40B form is how you enroll in Medicare Part B when enrollment doesn’t happen automatically. It’s a one-page request with three short sections. You complete it yourself, add the CMS-L564 employer verification form if you’re enrolling through a Special Enrollment Period, and send both to Social Security by mail, fax, in person, or online.
Who Actually Needs to File It
Most people never touch this form. If you started receiving Social Security retirement benefits at least four months before turning 65, you’re automatically enrolled in both Part A and Part B. The same is true if you’ve been receiving Social Security disability benefits for 24 months, or immediately upon disability benefits beginning if you have ALS.1Centers for Medicare & Medicaid Services. Original Medicare (Part A and B) Eligibility and Enrollment
You need the CMS-40B if you’re outside those automatic categories. The typical case: you turned 65, kept working, and stayed on your employer’s group health plan instead of taking Part B. When that job-based coverage ends, the CMS-40B is how you request Part B. The form is also used during the General Enrollment Period (January 1 through March 31) by anyone who missed their initial window.2Centers for Medicare & Medicaid Services. Request for Enrollment in Medicare Part B (Medical Insurance)
One boundary worth naming: if you don’t already have Part A, this isn’t your form. You apply for Medicare for the first time through Social Security, either online at SSA.gov, by calling 800-772-1213, or at a local office.3Social Security Administration. Sign Up for Medicare
Filling Out the Three Sections
The form is officially titled “Request for Enrollment in Medicare Part B (Medical Insurance).” You can download it from CMS.gov or pick one up at your local Social Security office.4Centers for Medicare & Medicaid Services. Request for Enrollment in Medicare Part B (Medical Insurance)
Section 1: Basic Information
Enter your Medicare number (it’s on your Part A card or in your my Social Security account), your full legal name, mailing address, phone number, and email address. Your name and address should match what Social Security has on file. If anything has changed, update it with SSA before you send the form.
Section 2: Enrollment Details
This section asks whether you had coverage through an employer or union group health plan since turning 65, and whether you served as an international volunteer for a nonprofit that provided health coverage. If either applies, fill in the start and end dates of that employment and coverage. A fourth question asks whether an employer or insurer pressured you to enroll in Part B; if so, explain the circumstances and attach any supporting documents.4Centers for Medicare & Medicaid Services. Request for Enrollment in Medicare Part B (Medical Insurance)
Section 2 also includes your coverage start date choice. If you’re enrolling during a Special Enrollment Period while still on employer coverage, or within the first full month after it ends, you can pick either the first day of the month you enroll or the first day of any of the three months after enrollment. Write your preferred month and year in the space provided.
Section 3: Signature
Sign and date the form. If you sign with a mark (an “X”), a witness must also print their name, sign, and date the form.
The CMS-L564 Employer Form
If you’re enrolling through a Special Enrollment Period based on employer coverage, submit the CMS-L564 alongside your CMS-40B. This form is the proof that you had group health plan coverage through current employment, which is what protects you from the late enrollment penalty.5Centers for Medicare & Medicaid Services. CMS L564
The CMS-L564 has two parts. You complete Section A with your own information. Then you hand the form to your employer (or former employer), and a company official completes Section B. Section B asks for the employer’s name and address, the dates your health coverage started and ended, the dates of employment, and requires the signature, printed title, and phone number of the person completing it.6Centers for Medicare & Medicaid Services. Medicare Request for Employment Information
The employer section does not ask for a tax identification number. It asks for the company name, address, coverage dates, employment dates, and a signature. Coverage dates matter most, since Social Security uses them to confirm you qualify for penalty-free enrollment. Double-check them against your insurance cards or benefits statements before your employer signs.
What if your employer won’t complete the form or you can no longer reach them? Social Security will accept other proof of prior coverage, such as pay stubs, W-2s showing insurance premium deductions, or benefits statements. Include whatever documentation you have and explain the situation in writing.
How to Submit
You have three ways to get your completed forms to Social Security.7Social Security Administration. Sign Up for Medicare Part B Online, by Fax, or by Mail
- Online. If you’re 65 or older and enrolling in Part B through a Special Enrollment Period, you can complete the application at SSA.gov. The process uses an electronic signature, so you need a valid email address. You can upload the CMS-L564 through your online account.
- Fax or mail. Send the signed CMS-40B (and CMS-L564, if applicable) to your local Social Security office. Find your local office and its fax number at SSA.gov/locator. If you mail the forms, use certified mail with a return receipt so you have proof they arrived within your enrollment window.
- In person. Bring the forms to your local Social Security office. Staff will stamp them with the date of receipt. Keep a copy of everything you hand over.
Time Your Filing to Your Enrollment Window
The window you use determines when your coverage starts and whether you’ll owe a penalty.
Initial Enrollment Period
Your Initial Enrollment Period is a seven-month window centered on the month you turn 65: the three months before your birthday month, your birthday month, and the three months after. File in the first three months and coverage starts the month you turn 65. File during your birthday month and coverage starts the following month. Each later month pushes the start date back another month.8Medicare. When Does Medicare Coverage Start?
Special Enrollment Period
If you delayed Part B because you had group coverage through your own or a spouse’s current employer, you get an eight-month Special Enrollment Period. It starts the month after employment ends or the group coverage ends, whichever comes first. During this window, you can apply any time of year and avoid late penalties.9Social Security Administration. Sign Up for Part B Only
Other events that trigger a Special Enrollment Period include moving out of a plan’s service area, being released from incarceration, losing Medicaid eligibility, and returning to the U.S. after living abroad. Each carries its own window, typically two to three months.10Medicare. Special Enrollment Periods
General Enrollment Period
Miss both of the above and you can sign up between January 1 and March 31 each year. Coverage starts the month after you enroll, and most people who use this window will owe a late enrollment penalty.8Medicare. When Does Medicare Coverage Start?
If you’re retiring on a specific date, work backward from that date to pick an enrollment month that gives you seamless coverage. For most people leaving employer plans, filing in the month employment or coverage ends, and choosing a start date of the following month, avoids any gap.
After You File
Processing times vary by enrollment period. Applications filed during the Initial Enrollment Period typically take two to six weeks. Special Enrollment Period applications can take four to eight weeks or longer, because Social Security has to verify your employer coverage. General Enrollment Period applications usually run four to six weeks.
About two weeks after your enrollment is confirmed, you’ll receive the “Welcome to Medicare” packet in the mail. It includes a letter, a booklet explaining your coverage and the decisions ahead, and your Medicare card.11Medicare. “Welcome to Medicare” Package (Not Automatically Enrolled)
If you need your Medicare number before the card arrives, sign in to your Social Security account at SSA.gov and view your benefit verification letter. It will show your number.12Social Security Administration. Manage Your Medicare Benefits
The Penalty for Filing Late
If you could have had Part B and didn’t sign up, and you don’t qualify for a Special Enrollment Period, you’ll pay a permanent surcharge. The penalty is 10% of the standard premium for every full 12-month period you were eligible but not enrolled. That amount is added to your premium for as long as you have Part B.13Medicare. Avoid Late Enrollment Penalties
The CMS-L564 is your protection against that penalty. When it shows continuous group health plan coverage through current employment, Social Security treats your enrollment as on time. An incomplete or inaccurate CMS-L564 can produce a penalty that stays with you for life, which is why the dates on that form are worth the extra care before you submit.