A True Step‑By‑Step Guide to Applying for Medicare Part B (After Employer Coverage)

If you’re turning 65 (or already over 65) and you stayed on an active employer group health plan (yours or your spouse’s), you typically enroll in Medicare Part B later using a Special Enrollment Period (SEP). This guide is written so you can follow it step by step.

Applying for Part B under the Special Enrollment Period (SEP)

Step 1a (only if needed): Apply Online for Medicare Part A first

If you don’t already have Part A, do this first. You’ll need your Medicare number to complete the Part B SEP process.

1. Go to Social Security’s Medicare sign‑up page:
   https://www.ssa.gov/medicare/sign-up
2. Complete the normal Medicare application online.
3. Important: There is no separate “Do you want Part A?” question.
   Finishing the application enrolls you in Part A.
4. When the application asks about Part B, choose “No” if you’re staying on employer coverage and only want Part A right now.
   (You’ll apply for Part B separately using the SEP steps below.)
5. After you complete the application, you’ll get a Medicare card/number. Keep it handy for Step 2.

Optional Part A walkthrough (extra detail here)

Step 1b: Get CMS‑L564 completed by your employer (or your spouse’s employer)

CMS‑L564 (“Request for Employment Information”) is what Social Security uses to confirm you had employer group health coverage based on active employment. This is what helps you qualify for the SEP and avoid a Part B late‑enrollment penalty.

Download CMS‑L564 here:
https://www.cms.gov/medicare/cms-forms/cms-forms/downloads/cms-l564e.pdf

What to do:

• Ask your (or your spouse’s) HR/Benefits department to complete CMS‑L564.
• Some employers fill out the whole form and send it back. Others will ask you to complete Section A (your info) and then they complete Section B (employer/coverage info).
• The employer is confirming employment dates and group health coverage dates — not the specific insurance company name.

Coverage date tips (this is where people mess it up):

• The dates should reflect when your group health coverage started with that employer (and when it ended, if it ended).
• Don’t use the date your plan renewed, changed carriers, or started a new plan year.
• Social Security is looking for continuous employer group coverage back to when you first became eligible (typically around your 65th birthday).

Good news:

• An electronic version is fine (HR can email it back).
• Electronic signatures from HR are acceptable.
• Save the completed CMS‑L564 as a PDF — it makes uploading much easier.

Full write up on Form CMS-L564

Step 2: Open the online Part B application (CMS‑40B online through Social Security)

You’ll complete the Part B application online using Social Security’s secure site.

1. Go to:
   https://www.ssa.gov/medicare/sign-up
2. Scroll to “Sign up for Part B only” and click Get Started
   (Or go directly here: https://www.ssa.gov/medicare/sign-up/part-b-only)
3. Click Start application
4. Review and agree to the terms of service
5. Scroll down and click Continue to open the application
6. Click the blue Start button on the left side of your screen to begin filling it out.

Step 3: Request your Part B start date (this is critical)

In Section A of the online application, there is a “Remarks” box (this is Question 7 on the paper form). This is where you tell Social Security exactly when you want Part B to begin.

In the Remarks box, type something like:

“I want my Medicare Part B coverage to begin on 05/01/2026.”

Rules for the date:

• Always use the 1st of the month (Part B starts on the first day of a month).
• This helps Social Security line up your Part B effective date with the end of your employer coverage so you don’t create a gap.

Step 4: Complete Section B so it matches CMS‑L564 exactly

Section B asks about your (or your spouse’s) employer coverage. It must match CMS‑L564.

If you’re covered under your spouse’s employer plan:

• Your name = the applicant
• Your spouse’s name = the employee

If it’s your employer plan:

• You are both the applicant and the employee.

Double‑check these items match CMS‑L564:

• Employer name and address
• Group health plan info
• Group coverage start date (month/year)
• Group coverage end date (if it ended)

If your employer coverage has not ended yet:

• It’s okay if HR leaves the coverage end date and employment end date blank on CMS‑L564.
• The online application should still allow you to proceed, and Social Security will use the Part B start date you requested in Remarks.

Step 5: Complete Section C using the correct coverage dates

Section C focuses on your health coverage dates with that employer. Again, it must match CMS‑L564.

Use:

• The date your group coverage began with that employer

Not:

• A recent carrier change date
• A renewal date
• A plan year start date

If coverage is ongoing:

• Fill in the start date
• Leave the end date blank (if that’s how HR completed CMS‑L564)

Step 6: Upload CMS‑L564 (employment verification)

In Section D, you’ll attach your proof of employer coverage.

Look for the area labeled:
“Click to attach employment verification”

Upload:

• Your completed CMS‑L564 PDF

Optional (only if needed):
You can also upload other proof (like an employer letter, pay stubs, tax documents showing health insurance deductions), but most people only need a correctly completed CMS‑L564.

Step 7: Sign, verify your email, and submit

1. In the signature section, type your first and last name exactly as it appears on your Social Security records.
2. The system will ask for an email address to verify your electronic signature and finalize the application.
3. After you submit:

• Check your email inbox for a message from Social Security asking you to verify your email.
• Click the verification link.
• You should then see confirmation that e‑signing is complete.

After that, you’ve successfully applied for Part B under your SEP. Social Security will review your submission and mail you a decision and/or an updated Medicare card showing your Part B effective date.

Paper form links (if you prefer fax/mail instead of online)

CMS‑40B (Part B Enrollment) PDF: Click the link below to print the document.
https://www.cms.gov/medicare/cms-forms/cms-forms/downloads/cms40b-e.pdf

CMS‑L564 (Employment Information) PDF: Click the link below to print the document.
https://www.cms.gov/medicare/cms-forms/cms-forms/downloads/cms-l564e.pdf

Common mistakes that delay Part B approvals

• Using the wrong “start date” (using a renewal date instead of the date coverage started with the employer)
• Employer name/address doesn’t match between the online application and CMS‑L564
• Forgetting to upload the CMS‑L564 PDF
• Leaving the Remarks box blank (so Social Security has to guess your Part B start date)