Form CMS-40B and CMS-L564: How to Enroll in Medicare Part B

If you're leaving a job or retiring and losing employer health coverage, you enroll in Medicare Part B by filling out two forms, not one: CMS-40B (your application) and CMS-L564 (proof of your employer coverage). Both are short, but the CMS-L564 has a section only your former employer can complete, so timing matters more than the paperwork itself. Here is exactly how to fill out each field on both forms and get them to Social Security before your window closes.

Who Needs These Forms and When

You need CMS-40B and CMS-L564 together only if you're applying for Medicare Part B through a Special Enrollment Period (SEP), meaning you (or your spouse) had group health plan coverage through current employment after you first became eligible for Medicare. If that describes you, Social Security wants documentation that you were covered continuously, with no more than 8 months without coverage, before it will waive the late enrollment penalty.

There are three situations where you'd use CMS-40B:

• Special Enrollment Period: You delayed Part B because you had employer coverage, and that coverage or your employment recently ended. You get 8 months from whichever comes first to sign up penalty-free, and this is when you need CMS-L564 too.
• General Enrollment Period: You missed your Initial Enrollment Period and had no employer coverage to justify the delay. You can only apply between January 1 and March 31 each year, and coverage starts the month after you sign up.
• Initial Enrollment Period in Puerto Rico: Residents of Puerto Rico must use CMS-40B to sign up for Part B during their IEP, since automatic enrollment doesn't apply there.

One common mix-up: the Medicare Annual Enrollment Period (October 15 to December 7) is for switching or adding Medicare Advantage and Part D drug plans once you already have Medicare. It has nothing to do with your initial Part B application. If you're signing up for Part B for the first time after leaving a job, you're on the SEP timeline described above, not the fall AEP calendar.

The stakes for getting the timing right are real. Miss your enrollment window entirely and your Part B premium goes up 10% for every full 12-month period you were eligible but not enrolled, for as long as you have Part B. With the standard 2026 Part B premium at $202.90 a month, that penalty compounds for years, so the paperwork is worth doing carefully the first time.

CMS-L564: Getting Your Employer's Section Completed

Start with CMS-L564 because it depends on someone else's schedule. The form has two sections:

Section A is yours to fill out: your name and Social Security number, the employee's name and SSN if that's not you (for example, if you're applying based on a spouse's coverage), and the employer's name and address.

Section B belongs to the employer or their HR/benefits contact. They confirm whether you were covered under the group health plan, the coverage start date and, if it ended, the end date, and the dates you actually worked there (or confirmation you're still employed). If your coverage involved an Hours Bank Arrangement, they also note whether hours remain in reserve and when they'll run out. A company official signs, dates, and lists a title and phone number.

In practice, HR departments handle this request rarely, so give them the form early and be specific about the deadline. Fill out Section A yourself first using PDF Editify's PDF form filler, save it, and email the partially completed PDF to your HR contact so all they have to do is complete Section B and sign. That removes the most common source of delay: an employer who isn't sure what information to provide.

If your former employer has gone out of business or refuses to complete the form, don't stall your application waiting on it. Contact Social Security directly. They can accept alternative proof, such as pay stubs showing health insurance deductions or a letter from the health plan.

CMS-40B: Step by Step

CMS-40B is a single page with 12 numbered fields. Here's what goes in each one:

• Field 1, Your Medicare Number: Found on your red, white, and blue Medicare card. You must already have Part A to use this form; if you don't, contact Social Security instead, since this form only adds Part B.
• Field 2, Do you wish to sign up for Medicare Part B? Mark "Yes."
• Field 3, Your Name: Last name, first name, middle name, in that order, matching what's on file with Social Security.
• Field 4, Mailing Address: Street number and name, P.O. Box, or route.
• Field 5, City, State, and ZIP code.
• Field 6, Phone Number: Include the area code.
• Field 7, Written Signature: Sign in cursive or your usual signature, not printed letters. If you're unable to sign, you can mark an "X," but then a witness must complete fields 9 through 11.
• Field 8, Date Signed.
• Fields 9-11, Witness Information: Witness signature, date, and address, only required if you signed with an "X" instead of a full signature.
• Field 12, Remarks: Optional; use this to clarify anything about your enrollment, such as noting that CMS-L564 is attached.

You can complete all of this in a browser without printing anything first. Open the CMS-40B PDF in PDF Editify's online PDF editor, type your answers directly into the fields, then add your signature with the e-signature tool so field 7 is a real signature rather than a scanned scrawl. If you'd rather see the general workflow first, our guide on how to fill out a PDF form online covers the same upload-edit-download steps used here.

Submitting Both Forms Together

Once CMS-40B is signed and CMS-L564 has your employer's Section B completed and signed, mail or fax both forms together to your local Social Security office. Do not send them separately or on different days; Social Security processes them as one SEP application, and a CMS-40B without its supporting CMS-L564 can get flagged for missing proof of continuous coverage.

Find your local office address and fax number at SSA.gov/locator. If you'd rather hand-deliver the forms, most offices accept walk-ins, though appointments move faster. Keep a copy of both signed forms for your own records before you send them, either as a photo or a saved PDF export.

This is exactly the kind of one-time task where paying for a full-year PDF subscription doesn't make sense. PDF Editify's One Week Plan is a $3 one-time payment with nothing to cancel afterward, versus committing to a recurring Adobe or DocuSign plan for two forms you'll fill out once. Compare options on the pricing page before you commit to a monthly plan you won't use again.

What Happens After You Submit

Social Security typically takes two to six weeks to process a Part B enrollment request submitted with employment verification. You'll receive a decision by mail, and if approved, an updated Medicare card showing your Part B effective date. If you signed up during your SEP while coverage was still active or in the first full month without it, your Part B start date can be as early as the first of the month you applied; sign up later in your 8-month window and coverage starts the month after you apply.

Once Part B is active, you'll be billed quarterly unless you're already receiving Social Security retirement benefits, in which case the premium is deducted automatically from your monthly check. You can also enroll in Medicare Easy Pay to have premiums withdrawn directly from a bank account instead of paying by mail. If your household income is above certain thresholds, expect an Income-Related Monthly Adjustment Amount (IRMAA) added to the standard premium; Social Security calculates this separately based on your tax return from two years prior and will notify you if it applies.

If Social Security later asks for more documentation, or if your employer's Section B was incomplete, respond quickly. Because the SEP is time-limited, delays in refiling paperwork can push your effective date later or, in rare cases, put you at risk of missing the window entirely.