CMS (Centers for Medicare & Medicaid Services) · United States

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Form CMS-40B: Application for Enrollment in Medicare Part B (Medical Insurance)

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Quick answer

Form CMS-40B, Application for Enrollment in Medicare Part B, is used to sign up for Medicare Part B (Medical Insurance) if you already have Part A and delayed Part B — typically during a Special Enrollment Period after employer coverage ends, or during the General Enrollment Period. It is often submitted alongside Form CMS-L564 (proof of employer coverage). With JustFill you upload the blank CMS-40B PDF, the AI maps each field, and you complete and download it free.

Form
Form CMS-40B
Issued by
CMS (Centers for Medicare & Medicaid Services)
Country
United States
Cost to fill
Free

What is Form CMS-40B?

CMS-40B enrolls you in Medicare Part B when you did not take it when first eligible — usually because you had group health coverage through current employment. You provide your Medicare number and enrollment details, and you generally pair it with Form CMS-L564 (Request for Employment Information) to prove the coverage that lets you avoid a late-enrollment penalty. JustFill lets you complete the CMS-40B online so your Medicare number and dates are clear before you submit it to Social Security.

Download the Form CMS-40B form PDF — free

The official Form CMS-40B PDF is free to download from CMS/Medicare at cms.gov. Open the blank PDF in JustFill to type your Medicare number and enrollment details, then download the completed form to submit to Social Security — usually together with Form CMS-L564.

Get the official Form CMS-40B PDF from CMS (Centers for Medicare & Medicaid Services)

Who fills out Form CMS-40B?

  • People with Medicare Part A who delayed Part B and now want to enroll
  • Beneficiaries enrolling during a Special Enrollment Period after employer coverage ends
  • Those signing up during the Medicare General Enrollment Period
  • Anyone pairing Part B enrollment with Form CMS-L564 to avoid a late penalty

Field-by-field breakdown

What each section of Form CMS-40B asks for. JustFill’s AI will detect these fields automatically when you upload the PDF — review the breakdown below so you know what to enter.

Applicant identification

Your name as it appears on your Medicare card and your Medicare number.

Enrollment details

Your request to enroll in Part B and the requested start date.

Remarks

Any special-enrollment context, often referencing your CMS-L564 employer coverage.

Signature

You sign and date the application.

Common mistakes to avoid

  • 1Submitting CMS-40B without Form CMS-L564 when claiming a Special Enrollment Period — the employer proof is usually required.
  • 2Using a Medicare number that does not match your card exactly.
  • 3Missing the enrollment window, which can cause a lifelong Part B late-enrollment penalty.

How JustFill helps you complete Form CMS-40B

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Related forms

CMS (Centers for Medicare & Medicaid Services)

CMS-L564

CMS-L564: Request for Employment Information (Medicare)

SSA (Social Security Administration)

Form SSA-44

Form SSA-44: Medicare Income-Related Monthly Adjustment Amount — Life-Changing Event

SSA (Social Security Administration)

Form SS-5

Form SS-5: Application for a Social Security Card

Frequently asked questions

To enroll in Medicare Part B if you have Part A but delayed Part B — typically during a Special Enrollment Period after employer coverage ends, or during the General Enrollment Period.
Usually yes, if you are enrolling through a Special Enrollment Period — CMS-L564 proves the employer coverage that lets you avoid a late-enrollment penalty. JustFill can fill both.
Yes. Upload the official PDF to JustFill — the AI detects each field and you type your Medicare details, then download the completed application to submit. No Adobe needed.
Submit it to Social Security (which administers Medicare enrollment) by mail, fax, or in person, following the instructions on the form. Fill it in JustFill first for a clean, legible application.

Official source: Form CMS-40B on CMS (Centers for Medicare & Medicaid Services)’s website

JustFill is an independent product and is not affiliated with, endorsed by, or sponsored by CMS (Centers for Medicare & Medicaid Services) or any government agency. Always verify your completed form on the official version before signing or submitting.