Fill out CMS-40B (Application for Enrollment in Medicare Part B) online
Form CMS-40B is used to apply for enrollment in Medicare Part B (Medical Insurance), which covers physician services, outpatient care, and other medical services. It is commonly used during a Special Enrollment Period (SEP) by individuals who delayed Part B enrollment because they had employer-sponsored health coverage.
How to fill out CMS-40B (Application for Enrollment in Medicare Part B)
Enter your personal information
Provide your name, date of birth, sex, Social Security number, and Medicare Beneficiary Identifier (MBI) number. Include your current mailing address and phone number.
Indicate your enrollment reason
Check the box indicating why you are enrolling. If you're applying during a Special Enrollment Period, indicate that you had group health plan coverage based on current employment.
Provide employment and coverage details
Enter the name and address of the employer providing group health plan coverage, and the date your employment or group health plan coverage ended (or will end).
Sign and date the form
Sign and date the application. If someone is signing on your behalf, they must indicate their relationship and provide documentation of their authority. Submit with Form CMS-L564.
About CMS-40B (Application for Enrollment in Medicare Part B)
Who needs this form
Medicare beneficiaries who already have Part A and want to enroll in Part B, particularly those who delayed enrollment because they or their spouse had employer-sponsored group health plan coverage.
Where to submit
Submit to your local Social Security Administration (SSA) office by mail or fax (1-833-914-2016). Often submitted together with Form CMS-L564. You can also enroll online at ssa.gov during a Special Enrollment Period.
Source and content freshness
- Filing deadlines may shift for weekends and holidays. Verify due dates with official instructions.
Common mistakes to avoid
- Not submitting CMS-L564 (proof of employer coverage) along with CMS-40B
- Missing the Special Enrollment Period deadline (8 months after employment or coverage ends)
- Confusing the General Enrollment Period with the Special Enrollment Period
- Not realizing that late enrollment penalties apply if you miss your enrollment window
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What is the difference between CMS-40B and CMS-L564?
CMS-40B is the actual application to enroll in Medicare Part B. CMS-L564 is a companion form that provides proof of employer-sponsored health coverage, which is required to qualify for a Special Enrollment Period without late penalties. You typically need to submit both forms together.
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