Fill Out Form CMS-40B Online
Application for Enrollment in Medicare Part B (Medical Insurance)
Centers for Medicare & Medicaid Services
Enrolls in Medicare Part B medical insurance, typically during a special enrollment period.
Reviewed July 2026
How it works
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Open the form. The official PDF loads straight into the editor, no download needed first.
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Fill it out in the editor. Click anywhere to type, add checkmarks and place your signature.
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Form CMS-40B, Application for Enrollment in Medicare Part B (Medical Insurance), is the form used to sign up for Medicare Part B when you were not enrolled automatically. It is most often filed by people who delayed Part B because they had group health coverage through an employer and are now using a special enrollment period.
You can fill out the CMS-40B in the Universal PDF editor and download the finished PDF to sign and submit to Social Security. If you are enrolling based on employer coverage, plan to submit Form CMS-L564, the employment information form, along with it.
What is Form CMS-40B used for
Part B covers doctor visits, outpatient care, and other medical services, and enrollment is not always automatic. The CMS-40B is the application you file with the Social Security Administration to add Part B when:
- You already have Part A and want to add Part B
- You delayed Part B because you or your spouse kept working and had employer group health coverage, and you now qualify for a special enrollment period
- You are enrolling during another period when Social Security instructs you to file this form
Who files Form CMS-40B
People eligible for Medicare who are not enrolled in Part B and were not signed up automatically. The most common filer is someone past their initial enrollment period who stayed on an employer plan; the special enrollment period generally lets you sign up while you have that coverage or within eight months after the employment or the coverage ends, whichever comes first.
Enrolling on time matters, because going without Part B when no other qualifying coverage is in place can lead to a late enrollment penalty that increases the monthly premium for as long as you have Part B.
How to fill out Form CMS-40B
The form itself is short:
- Your Medicare number, exactly as it appears on your Medicare card
- Your name, mailing address, and phone number
- The signature and date, plus a witness section if you sign with a mark
- The remarks area, where applicants often note the Part B start date they are requesting and that they are enrolling under a special enrollment period
- If you are using the special enrollment period, attach Form CMS-L564 completed by your or your spouse's employer as evidence of group health coverage
Where to send it
The CMS-40B goes to the Social Security Administration, not to CMS. You can submit it to your local Social Security office by mail or fax, and SSA also offers an online path for Part B special enrollment through ssa.gov. Check ssa.gov or call your local office for the current submission options before sending your form.
Frequently asked questions
If you are enrolling under a special enrollment period based on employer group health coverage, yes. The L564, completed by the employer, is the proof of coverage that supports your penalty-exempt enrollment.
Generally while you are covered by a group health plan based on current employment, yours or your spouse's, or within eight months after that employment or coverage ends, whichever comes first. COBRA and retiree coverage do not count as current employment coverage.
You may have to wait for the general enrollment period to sign up, and a late enrollment penalty can permanently increase your Part B premium. If you think you qualify for an exception, contact Social Security.
To the Social Security Administration. You can mail or fax it to your local Social Security office, and SSA offers an online submission option for special enrollment cases through ssa.gov.
Yes. Open the form in the Universal PDF editor, type your information, and download the completed PDF to sign and submit along with any required evidence.
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