Enrolling in Medicare After Your Initial Enrollment Period
- Jamon White
- May 12
- 7 min read
A guide to the Special Enrollment Period (SEP) application process
INTRODUCTION
If you delayed signing up for Medicare past age 65 because you were covered under an active employer group health plan — yours or your spouse's — you can still enroll without a late penalty by using a Special Enrollment Period (SEP). Most people use the SEP either while still working or within the eight-month window that follows the loss of that employer coverage.
This page walks through the four most common enrollment scenarios, explains the two forms you'll typically need, and lays out every available way to submit your paperwork to the Social Security Administration.
Which Scenario Fits Your Situation?
Pick the scenario below that most closely matches your circumstances. Each one outlines the steps, the timing, and the forms involved.
Scenario 1: You Already Have Part A and Just Need to Add Part B
Submit up to 3 months before your requested start date
If you signed up for Part A when you turned 65 (which many people do because it's typically free) and now want to add Part B because you're losing your employer coverage or simply want to start using Medicare as your primary insurance, this is the cleanest path.
Complete and submit Form CMS-40B (your part) and Form CMS-L564 (your employer's part) directly to Social Security. Both forms are described in detail in the next section.
While you're still actively employed and covered under that group plan, you can submit the forms up to three months before you want Part B to start.
However, once you've separated from that employer, Part B will begin the month after the paperwork is submitted — you can no longer pick a future start date once you're outside active employment.
Scenario 2: You Need Both Part A and Part B (But Not Social Security Yet)
Submit up to 3 months before your requested start date
If you didn't sign up for Part A at 65 and now need both Part A and Part B, you'll do this in two steps:
Start by completing the online Medicare Only application at ssa.gov/benefits/medicare. When the application asks if you want Part B, answer YES. Part A is included automatically and may be backdated up to six months from the month you submit the application.
Then submit Form CMS-40B and Form CMS-L564 to Social Security. Because you don't yet have a Medicare number when filling out these forms, write your Social Security Number in place of the Medicare number on Form CMS-40B.
Scenario 3: You Need Medicare and Social Security at the Same Time
Submit up to 3 months before your requested start date
If you're ready to start collecting Social Security retirement benefits and enroll in Medicare at the same time, you can roll both into a single online application:
Begin the online Social Security retirement benefits application at ssa.gov. The retirement application includes a section asking whether you'd like Part B. Answer YES.
Specify when you want Part B to begin in the appropriate section
Submit Form CMS-40B and Form CMS-L564 as well. If you don't have Part A yet, use your Social Security Number on Form CMS-40B in place of the Medicare number.
If you didn't already have Part A, it'll be added automatically and may be backdated up to six months.
Scenario 4: You Don't Have 40 Quarters of Medicare-Covered Work — Enrolling Through a Spouse
Schedule by phone (or in-person) up to 3 months before your start date
If you don't personally have 40 quarters (about 10 years) of work history that paid into Medicare, you may still qualify for premium-free Part A through your spouse's work record. Three conditions must be met:
You have been married to your spouse for at least one year
Your spouse is at least 62 years old
Your spouse has 40 quarters of Medicare-covered employment
This type of enrollment cannot be completed online. You'll need to schedule a phone or in-person appointment with Social Security. Call your local SSA office or the main SSA number at 1-800-772-1213 to set up the appointment. Because appointments are often booked one to two months out, start calling about three to four months before you want Part B to begin.
For this scenario, you'll only need to submit Form CMS-L564, which can be uploaded, mailed, faxed, or hand-delivered to SSA.
Walk-in availability at SSA offices varies — some accommodate walk-ins readily, others do not. The "Submitting Your Forms" section below covers all available submission methods, including when an in-person walk-in might be your fastest option.
Forms You'll Need
Form CMS-40B — Application for Enrollment in Medicare Part B
This is the form you complete. It's the official request to enroll in Medicare Part B and is required for Scenarios 1, 2, and 3 above. The official PDF is available at cms.gov.
A few practical notes when filling it out:
Each person enrolling in Part B needs their own form. If you and your spouse are both signing up, you'll each complete a separate CMS-40B.
Be sure to indicate when you'd like Part B to begin in the appropriate space at the bottom of the form.
If you don't have a Medicare number yet (you haven't enrolled in Part A), write your Social Security Number in the Medicare number field instead.
The employment dates you provide on Section 2, Question 3 should match the dates your employer enters on Section B of Form CMS-L564 (see below).
Form CMS-L564 — Request for Employment Information
This form is completed by your employer (or your spouse's employer, if you're enrolling based on their group health coverage). It documents the employer-sponsored health plan that allowed you to delay Part B without penalty. The official PDF is available at cms.gov.
The form is divided into two sections: Section A is filled out by you, and Section B is filled out by the employer.
If both you and your spouse are enrolling in Medicare, the employer needs to complete a separate CMS-L564 for each of you.
If you've had more than one qualifying employer since turning 65, you'll need a CMS-L564 from each one.
Submitting Your Forms
SSA accepts these forms several different ways. Uploading through your online SSA account has become the most efficient method, but mail, fax, and (in limited cases) in-person delivery are still available.
Option 1: Upload Through Your My Social Security Account
This is now the recommended approach. The documents are routed directly to your local SSA office for processing, and you'll get faster confirmation than with mail or fax. The process generally goes like this:
Sign in to your account at ssa.gov/myaccount.
From the dashboard, choose Upload Documents.
When prompted for the document type, select SSA Form.
From the form drop-down menu, select CMS-40B.
On the upload screen, drag and drop or browse to attach your completed CMS-40B. For SEP applications, you'll also upload your CMS-L564 here as a separate file.
Review and submit. You'll see a confirmation screen once everything has been received.
Option 2: Mail, Fax, or In-Person Delivery
If you prefer to submit on paper, both forms (CMS-40B and CMS-L564) need to go to your local Social Security office. You can find the office assigned to your ZIP code, including its mailing address, phone number, and direct fax number, using the SSA Office Locator at secure.ssa.gov/ICON/main.jsp.
By Mail
Make a copy of every page for your records before mailing. USPS Priority Mail is a good choice because it includes delivery confirmation. Processing time varies by office and time of year — expect at least a few weeks.
By Fax
Faxing directly to your local SSA office's direct fax number (found via the office locator above) is faster than the national fax line. Include a cover sheet noting the total page count.
If a local fax number isn't available, you can fax to the SSA National Fax line at 833-914-2016, but processing times tend to be longer through this route.
Office Drop Box
Most SSA offices have a drop box for paperwork. Place your forms in a sealed envelope and drop them off — but always make a copy first, as paperwork can occasionally be misplaced. Most offices are open Monday through Friday, generally 9:00 a.m. to 4:00 p.m.
In-Person Walk-In (Varies by Office)
Availability of this option varies from office to office. When it's available — particularly for adding Part B only — walking in and asking a representative to process your forms in person can be the fastest way to get Part B approved. Not every office will accommodate this, but when time is of the essence, it can produce the quickest turnaround.
If you do go this route, make a copy of your paperwork beforehand and ask the representative to process everything at the service window while you wait. When that works, online confirmation often appears in your SSA account within a few days.
Confirming Your Enrollment
Depending on timing and your local office's workload, you'll typically receive a confirmation letter in the mail within two to six weeks. Your updated Medicare card follows shortly after.
You don't have to wait for the mail, though. The fastest way to confirm your enrollment is by checking your Benefit Verification Letter inside your online My Social Security account. The Medicare Information section of that letter will show your Medicare number and the start dates for Part A and Part B once they've been processed.
One quick note on the letter itself: it displays a "BNC#" in the upper right corner, but that is not your Medicare number. Your Medicare number appears specifically in the Medicare Information section of the letter, alongside your Part A and Part B effective dates.
The Benefit Verification Letter itself counts as proof of Medicare coverage. Once your Medicare number and effective dates show up there, you can use the letter to apply for a Medigap plan, a Part D drug plan, or a Medicare Advantage plan — there's no need to wait for the physical card to arrive.
Helpful Reference Links
SSA.gov — the Social Security Administration's main website
My Social Security Account — ssa.gov/myaccount (sign in or create an account)
Medicare Only Application — ssa.gov/benefits/medicare
SSA Office Locator — secure.ssa.gov/ICON/main.jsp
Form CMS-40B (PDF) — cms.gov/medicare/cms-forms/cms-forms/downloads/cms40b-e.pdf
Form CMS-L564 (PDF) — cms.gov/medicare/cms-forms/cms-forms/downloads/cms-l564e.pdf
Medicare.gov — the official Medicare website
Have Questions?
If you have any questions about the information on this page, feel free to reach out — we're happy to help point you in the right direction.
(512) 298-5404
This page is provided for informational purposes only and does not constitute legal, tax, or financial advice. Four Oaks is not affiliated with the Social Security Administration or the federal Medicare program.
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