Medicare · Supporting
CMS-40B, the form to sign up for Part B
Last reviewed Invalid Date4 min readBy the Goodsurance editorial team Reviewed by the Goodsurance editorial team
CMS-40B is the form you use to enroll in Medicare Part B when you did not get it automatically. Most people who are already receiving Social Security are enrolled in Part A and Part B without lifting a finger. But if you delayed Part B, or you are signing up during a Special Enrollment Period after leaving a job, you often have to ask for it, and CMS-40B is how you ask. Here is when you need it, what goes with it, and how to file it.
What CMS-40B is for
The short version: CMS-40B is the application to enroll in Medicare Part B when enrollment is not automatic. You use it if you already have Part A and now want to add Part B, most often after delaying it because you were still working.
Its full name is the Application for Enrollment in Medicare Part B. You reach for it when Medicare did not sign you up for Part B on its own, which is common if you turned it down at 65 because you had employer coverage, or if you are enrolling later during a Special Enrollment Period. If you are already getting Social Security benefits, you were likely enrolled in Part B automatically and do not need this form at all.
In short: CMS-40B is how you add Part B when it did not happen automatically.
When you need it, and the timing that matters
The form itself is simple; the timing around it is what protects you.
- If you delayed Part B because of current employer coverage, you generally have an 8-month Special Enrollment Period after that job or coverage ends to sign up without a penalty.
- If you miss your windows, Part B has a late enrollment penalty of 10 percent for each full 12 months you could have had it but did not, and that surcharge is usually permanent.
- COBRA and retiree coverage do not count as the current employer coverage that protects your Special Enrollment Period, so do not wait on those.
In short: file CMS-40B inside your enrollment window, because the penalty for missing it lasts for life.
What to file with it
If you are enrolling through a Special Enrollment Period tied to employer coverage, you usually file CMS-40B together with a second form, CMS-L564, which is the request for employment information that your employer completes to prove you had that coverage. Having both ready avoids delays. You can submit these to Social Security, which administers Medicare enrollment, online, by mail, by fax, or in person.
In short: CMS-40B often travels with CMS-L564, the employer proof of coverage, when you enroll after leaving a job.
After you file
Once Social Security processes the application, you will get confirmation and a start date for your Part B coverage, and your Medicare card will reflect both Part A and Part B. If your timing or your situation is complicated, for example if you are juggling employer coverage, COBRA, or an HSA, the order and dates of these steps can change what you owe.
If you are not sure which window you are in or what to file, please contact us to discuss your options.
In short: file the form, watch your start date, and get help with the timing if your coverage situation is not simple.
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What is form CMS-40B used for?
CMS-40B is the Application for Enrollment in Medicare Part B. You use it to sign up for Part B when it did not happen automatically, most often because you delayed Part B while you had employer coverage and now want to add it. People already receiving Social Security are usually enrolled in Part B automatically and do not need the form.
Do I need any other forms with CMS-40B?
If you are enrolling during a Special Enrollment Period based on current employer coverage, you generally also file CMS-L564, the request for employment information that your employer completes to confirm your coverage. Submitting both together helps avoid delays. You file with Social Security, which handles Medicare enrollment.
What happens if I file late?
Part B has a late enrollment penalty of 10 percent for each full 12 months you could have had Part B but did not, and it is usually permanent. If you delayed because of current employer coverage, you have an 8-month Special Enrollment Period after that coverage ends to enroll without a penalty. COBRA and retiree coverage do not protect that window, so timing matters. Please contact us to discuss your options.
References
- Medicare.govHow and when to sign up for Part B, including the CMS-40B application.
- SSA.govSocial Security administers Medicare enrollment and processes the Part B application.
- CMS.govForm CMS-40B, Application for Enrollment in Medicare Part B, and the CMS-L564 employer request.