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Quick answer: There’s no central fax number for Medicare Part B forms. You fax CMS-40B, plus CMS-L564 if you’re signing up because job-based cover is ending, to your local Social Security office. Its fax number is in SSA’s office locator. The 1-833-914-2016 number that still circulates comes from a 2020 SSA post; SSA’s current guidance doesn’t use it. If group cover is the reason you’re enrolling, the online application is usually quicker than either.
These forms are for people who already have Part A and need to add Part B, most often after retiring or coming off an employer’s health plan. Social Security handles the enrolment for Medicare, so that’s where the forms go, not to Medicare itself. Everything below was checked against SSA, CMS and Medicare.gov pages on 15 October 2026.
Where to fax your Part B forms
To your local field office. SSA’s Part B page says: “Find your Social Security office and fax or mail us the completed form.” Both current forms say the same, and so does SSA’s own staff manual, which tells staff that “the address and fax numbers can be obtained by accessing Social Security Office Locator”.
- Online: enter your ZIP code in the office locator. SSA confirmed in May 2025 that the listing shows each office’s mailing address and fax number.
- By phone: 1-800-772-1213 (TTY 1-800-325-0778), Monday to Friday, 8am to 7pm. Ask for the fax number of the office that serves your address.
- Railroad workers enrol through the Railroad Retirement Board instead, on 1-877-772-5772.
About 1-833-914-2016. An SSA blog post last updated in August 2020 gave this number for faxing CMS-40B and CMS-L564. SSA republished the same advice in October 2024, and the newer version sends the forms to your local office with no central number. Neither the current forms nor SSA’s Part B page mention it either. We wouldn’t send a Part B application there.
The forms, and who fills in what
Current editions as of October 2026.
| Form | What it is | Who completes it | When you need it |
|---|---|---|---|
| CMS-40B (07/2025) | Request for Enrollment in Medicare Part B. SSA’s pages still call it the “Application for Enrollment”; it’s the same form. | You | Always, to add Part B when you already have Part A |
| CMS-L564 (03/2025) | Medicare Request for Employment Information: proof you had group health cover through current work. | Section A: you. Section B: the employer | When you’re using the Special Enrollment Period after job-based cover |
| CMS-10797 | The Special Enrollment Period (Exceptional Conditions) application, for Part A and Part B. | You | Special situations; Medicare.gov’s examples include losing Medicaid and natural disasters |
Can you still sign up now?
Timing matters more than the fax number, because a late Part B application costs money for as long as you have Part B. Medicare.gov sets out the windows:
- Special Enrollment Period. If you (or your spouse) had group health cover through current employment, you can sign up any time you’re still covered, or within 8 months of the job or the cover ending, whichever happens first. COBRA doesn’t count as group cover, Medicare.gov notes.
- General Enrollment Period. Otherwise, 1 January to 31 March each year. Cover starts the month after you sign up.
- The penalty. Medicare.gov’s penalty page puts it at 10% of the standard premium for each full 12-month period you could have had Part B but didn’t. For most people it lasts as long as they have Part B. You generally avoid it if you sign up in a Special Enrollment Period.
When your employer won’t fill in Section B
Section B is the one part you can’t do alone, and a former employer may be slow, may have closed, or may never have seen the form. Medicare.gov’s instruction is to complete Section B of CMS-L564 yourself “as best you can, but don’t sign it”, and send proof of the job-based cover alongside it.
SSA’s staff manual lists what counts as that proof. One of these is enough:
- income tax returns that show health insurance premiums paid
- W-2s showing pre-tax medical contributions
- pay stubs that show health insurance premium deductions
- health insurance cards with a policy effective date
- explanations of benefits paid by the group health plan
- statements or receipts showing payment of health insurance premiums
The same manual says a field office can accept a letter, fax or email from the employer or the plan as evidence. If your old HR department will write a short letter confirming your dates of cover, that works too.
Picking your start date
Older SSA advice, including the 2024 blog post, says to write “I want Part B coverage to begin (MM/YY)” in the remarks section. The current 07/2025 CMS-40B has no remarks section. Instead there’s a box to choose when cover starts, which applies if you’re still on a group plan through current work, or in the first full month after leaving it: the first day of the month you enrol, or the first day of any of the next three months (write the month and year). If you’re using an old copy of the form, swap it for the current one before you send it.
Sending it
- Fill in CMS-40B and sign it. Add CMS-L564 and your evidence if you’re enrolling after job-based cover.
- Look up your office’s fax number in the locator, or call 1-800-772-1213 and ask.
- Put a cover sheet on top with your name, a phone number, the office you’re sending to and the page count. SSA doesn’t prescribe one; it just stops loose pages drifting. Our cover sheet generator makes one in a minute.
- Send everything in one fax, so the forms and evidence arrive together.
- Keep the transmission report. SSA publishes no fax confirmation, and if the timing is ever questioned, that timestamp shows you applied inside your window.
SSA doesn’t publish a processing time for faxed applications. What it does say is that incorrect or incomplete documents can delay or sink an application, and that once it’s processed, a new Medicare card comes in the post. If a few weeks pass with nothing, ring your local office with the date and time from your fax report.
Applying online instead
If you’re signing up because group cover is ending, SSA has an online form for exactly that, linked from its Part B page. You fill in CMS-40B and CMS-L564 on screen, upload your evidence, and sign electronically, which needs an email address. SSA’s staff manual adds that you can’t save it half-done and come back, and that it doesn’t cover the exceptional-conditions periods (CMS-10797) or international volunteers. Those still go by fax or post.
Claims and appeals: that’s your MAC, not Social Security
Social Security only handles signing up. Once you have Medicare, your claims are paid by a Medicare Administrative Contractor (MAC), a private company CMS assigns by region. CMS lists 12 regional MACs for Part A and Part B claims and four more for medical equipment and supplies. So if you’re searching for a Medicare fax number because a claim was denied, the number you want belongs to a MAC, and the SSA numbers above won’t reach it.
To appeal, Medicare.gov’s appeals page tells you to send the Redetermination Request Form (CMS-20027), or a signed letter, to the address in Step 7 on the last page of your Medicare Summary Notice, by the deadline printed on the notice. CMS puts that deadline at 120 days from when you received the notice, and says the MAC usually decides within 60 days. Neither page mentions fax for patients.
The MAC fax numbers you’ll find in a search are printed on pages and forms written for doctors and suppliers. Novitas’s Part B redetermination form, for example, gives a fax number but asks for the provider’s Medicare ID. If you’re the patient, post your appeal to the address on your notice and keep a copy. If your doctor’s office is appealing the same claim, it can use its MAC’s fax or online portal.
No fax machine? Municorn Fax sends forms from your phone: scan them with the camera, enter your office’s number, and you get a delivery report to keep. Your first single-page test fax is free. If you’d rather work from a computer, EveryFax sends faxes from your email and has a two-week trial. For the rest of what SSA takes by fax, see our Social Security fax guide.
Can I fax Part B forms during the General Enrollment Period?
Yes. CMS-40B covers the General Enrollment Period (1 January to 31 March) as well as the Special Enrollment Period, and it goes to your local office the same way. You don’t need CMS-L564 unless you’re claiming the Special Enrollment Period based on group cover.
Does Medicare have its own fax number for enrolment?
No. For people who already have Part A, Part B enrolment runs through Social Security, which is why every current form and SSA page points you to your local office. Medicare.gov says the same: you can send the completed forms to your local Social Security office by fax or mail.
Is 1-833-914-2016 still the Medicare Part B fax number?
Current SSA guidance doesn’t use it. It appears on a 2020 SSA blog post; SSA’s 2024 version of the same advice, the current CMS-40B and SSA’s Part B page all send the forms to your local office instead.
What if my employer has gone out of business?
Complete Section B of CMS-L564 yourself as best you can, leave it unsigned, and send one of the documents in the evidence list above, such as old pay stubs showing health insurance deductions or a W-2 with pre-tax medical contributions.
Is there a Medicare fax number for claims or appeals?
Not a single one. Claims are handled by regional Medicare Administrative Contractors, and appeals go to the address in Step 7 of your Medicare Summary Notice. The fax numbers MACs publish are aimed at doctors and suppliers.
How will I know Social Security received it?
SSA doesn’t mention sending a fax receipt, so keep your transmission report, and expect a new Medicare card in the post once the application is processed. If nothing arrives, call your local office with the date and time of your fax.
Sources
- SSA, Sign up for Part B only (updated 5 May 2026)
- SSA blog, Sign up for Medicare Part B online, by fax, or by mail (17 October 2024)
- SSA blog, the 2020 version of that post (last updated 6 August 2020), the source of 1-833-914-2016
- SSA blog, How to contact Social Security (1 May 2025), on fax numbers in the office locator
- CMS, CMS-40B (07/2025) and CMS-L564 (revised 03/2025)
- SSA POMS HI 00805.277 (effective 27 August 2024) and HI 00805.295 (effective 20 December 2024)
- Medicare.gov, Appeals in Original Medicare; CMS, First level of appeal: redetermination (modified 10 March 2026), CMS-20027 (01/20) and Who are the MACs (modified 10 September 2024)
- Novitas Solutions, Medicare Part B redetermination request form (FP152, R3.12.26)
- Medicare.gov, When does Medicare coverage start?, Ready to sign up for Part A and Part B and Avoid late enrollment penalties
- All checked on 15 October 2026.
