Complete Your Medicare Part B Application Without Missing a Required Step

To fill out Medicare form CMS-40B, first confirm that you already have Medicare Part A. Use the current official form, complete every applicable field in order, attach CMS-L564 if you are relying on qualifying current-employment group health coverage, sign and date the application, and submit it to Social Security—not CMS. CMS-40B requests Part B enrollment, but it does not by itself prove eligibility for a particular enrollment period, effective date, or penalty exception.

First, confirm that CMS-40B is the right form

Start by matching your situation to the correct enrollment route.

Your situation	Usual route	Key point
You already have Part A and want Part B	CMS-40B or an applicable online Part B-only application	CMS-40B may be used during an Initial, General, or eligible Special Enrollment Period
You do not have Part A	Social Security’s first-time Medicare enrollment process	Do not use CMS-40B by itself
You delayed Part B because of current-employment group coverage	CMS-40B plus CMS-L564, or an applicable online route	Social Security determines whether the coverage qualifies
You are applying under certain exceptional conditions	CMS-10797	Do not assume CMS-40B is the correct form

CMS describes CMS-40B as the form for someone who already has Medicare Part A and wants to enroll in Part B. The official version listed by CMS is revised July 1, 2025, and the form may be used during an Initial Enrollment Period, the January 1–March 31 General Enrollment Period, or an eligible Special Enrollment Period. Check the official CMS-40B form page and download the current version before entering any information.

If you do not already have Part A, contact Social Security and use its first-time Medicare enrollment process rather than submitting CMS-40B alone. If you already have Part A and are ending employer group health coverage, Social Security may allow you to use its online Part B-only application.

Some Special Enrollment Periods based on exceptional conditions use CMS-10797 instead. The appropriate form depends on why you are enrolling, so review Medicare’s official enrollment-form descriptions or ask Social Security if you are unsure.

CMS-40B is an application. Submitting it does not establish that you qualify for a Special Enrollment Period, guarantee a requested coverage date, or eliminate a possible late-enrollment penalty.

Gather the information and documents before you start

Have these items ready:

• Your Medicare number
• Your legal first, middle, and last name, plus any suffix
• Your mailing address
• Your phone number
• Your email address
• Applicable employment or volunteer-work start and end dates
• Applicable employer or union health-plan coverage dates
• An employer-completed CMS-L564 if you are relying on employment-based coverage
• Any documents requested for your enrollment circumstances
• A brief explanation and supporting records if an employer, insurer, or another entity asked or required you to enroll in Part B

The current form says all fields are required unless marked otherwise. Missing information, inconsistent dates, absent documents, or an unsigned application may prevent Social Security from making a timely and accurate eligibility decision.

If you cannot locate your Medicare number, do not substitute your Social Security number based on an unofficial workaround. The official CMS-40B instructions do not authorize that substitution. Contact Social Security and ask how to proceed.

When helping someone else complete the application, work from the applicant’s Medicare, employment, and coverage records. This can reduce mismatched names or dates across CMS-40B, CMS-L564, and supporting documents.

Complete Section 1: your identifying and contact information

Complete the first section in the order shown on the current form:

1. Medicare number: Copy the number from the applicant’s Medicare card or Medicare records.
2. Name: Enter the applicant’s first, middle, and last name. Add a suffix, such as Jr. or III, when applicable.
3. Mailing address: Enter the street address, P.O. Box, or route where the applicant can reliably receive correspondence.
4. City, state, and ZIP code: Complete every part of the mailing address.
5. Phone number: Use a number where Social Security can reach the applicant.
6. Email address: Enter an email address the applicant checks regularly.

Copy identifying information from Medicare records rather than relying on memory. A missing suffix, shortened legal name, or transposed Medicare number may lead to follow-up questions.

Use a stable mailing address. Social Security may send requests for clarification or communicate its decision by mail, so avoid an address where correspondence is likely to be missed.

Treat the Medicare number and supporting records as sensitive personal information. Do not place a real Medicare number, birth date, address, or other identifier in online examples, public comments, or messages sent to Insurance Roster.

Form labels and numbering can change. If the current official PDF differs from this walkthrough, follow the form and its accompanying instructions.

Complete Section 2: coverage, employment, and enrollment details

Section 2 asks about circumstances that may affect how Social Security evaluates the application. Answer each applicable yes-or-no question instead of leaving it blank.

First, indicate whether the applicant has had coverage through an employer or union group health plan since turning 65. Base the answer on the applicant’s actual coverage history. Do not assume that every plan associated with a former employer, union, or workplace qualifies for an employment-based Special Enrollment Period.

Next, answer the separate question about whether the applicant is or was an international volunteer for a nonprofit organization that provided health coverage. This is different from the employer or union coverage question and must be answered independently.

When the form requests dates, report these periods separately:

• Employment or volunteer-work period
• Health-plan coverage period

Use mm/yyyy format. For example, enter March 2024 as 03/2024, not 3/24.

Employment and coverage dates may differ. Someone might start work before becoming eligible for the health plan, or coverage might continue after work ends. Use the employer’s or plan’s records rather than changing dates simply to make them match.

If multiple periods do not fit, the form permits an additional sheet. As a practical organizational precaution—not a separate CMS requirement—identify the applicant, name the field being continued, and list the additional periods clearly. Include only records that support the application or that Social Security has requested.

The form also asks whether an employer, insurer, or another entity asked or required the applicant to enroll in Part B. If the answer is yes, explain who made the request, why enrollment was requested, and include supporting documentation.

Do not describe COBRA, retiree insurance, or any plan with an employer connection as qualifying current-employment coverage without confirmation. Social Security determines whether the employment and group-health-plan relationship satisfies the enrollment rules. Social Security or a State Health Insurance Assistance Program counselor can help review the situation.

Request a Part B start date only when the form allows it

Not every CMS-40B applicant may choose a coverage start date. The available date depends on the enrollment period and the applicant’s circumstances.

The current form provides a start-date choice in specified situations involving group health coverage based on current employment, including enrollment during the first full month after that coverage ends. An eligible applicant may request the first day of the enrollment month or the first day of one of the following three months. Approval remains subject to the applicable rules and Social Security’s decision. The form also states that Part B premiums are due for every month in which the applicant has Part B coverage, making the effective date financially consequential. These restrictions and options appear in the current CMS-40B instructions.

General timing works as follows:

Enrollment period	General timing
Initial Enrollment Period	Start date depends on the month of enrollment
General Enrollment Period, January 1–March 31	Coverage generally starts the following month
Special Enrollment Period	Timing varies by the qualifying circumstances

During the Initial Enrollment Period, Part B generally starts in the month a person turns 65 if enrollment occurs before that month. If enrollment occurs during the birthday month or in the following three months, coverage generally starts the next month. During the General Enrollment Period, coverage generally starts the month after enrollment. Special Enrollment Period timing depends on the qualifying situation, as detailed in Medicare’s coverage-start guidance.

Do not request a date only because it is convenient, and do not assume Social Security will approve it. If employer coverage is ending, verify its final day and the available Part B start dates with Social Security before submitting the application, particularly if a coverage gap is possible.

Add CMS-L564 when enrollment is based on employer coverage

CMS-L564 is conditional. It is not required with every CMS-40B application.

Form	Purpose
CMS-40B	Requests enrollment in Medicare Part B
CMS-L564	Supplies employment and group-health-plan information for an employment-related enrollment situation

Medicare describes CMS-L564 as proof used when a person is still working, retired within the last eight months, or lost job-based health coverage within the last eight months. Social Security still decides whether the applicant’s circumstances satisfy the enrollment requirements.

The applicant completes the applicant portion of CMS-L564. The employer generally completes the employment-verification portion, including the relevant employment and group-health-plan information.

Two examples show how the applicant and employee names work:

• Coverage through your own job: You are both the Medicare applicant and the employee.
• Coverage through a spouse’s job: You are the applicant and covered person; your spouse is the employee.

Review CMS-40B and CMS-L564 together before filing. Names, employment periods, and coverage dates should be consistent. If dates differ for a legitimate reason—for example, employment began before health benefits took effect—make sure each form accurately answers what its field asks.

If an employer will not complete CMS-L564, contact Social Security and ask what evidence it will accept for your circumstances. Do not assume that a document suggested by an unofficial source automatically replaces employer verification.

Sign, review, and submit the application to Social Security

The applicant must sign and date CMS-40B. If the applicant signs with an X, a witness who knows the applicant must provide the witness’s name, signature, and date.

Before submitting, check every item:

• [ ] Medicare number is entered correctly
• [ ] Full legal name and contact details are complete
• [ ] Every applicable yes-or-no question is answered
• [ ] Employment, volunteer, and coverage dates use mm/yyyy
• [ ] A requested start date is included only when applicable
• [ ] Required explanations and supporting documents are attached
• [ ] CMS-L564 is attached when the enrollment situation requires it
• [ ] Names and dates are consistent across the forms
• [ ] CMS-40B is signed and dated
• [ ] Witness details are present if the applicant signed with an X

Mail or fax the signed form and attachments to the applicant’s local Social Security office. CMS also permits in-person delivery to that office. Use SSA.gov/locator to find the correct destination; there is no single universal mailing address for every CMS-40B application.

Do not send CMS-40B or personal records to the CMS Paperwork Reduction Act Reports Clearance Office. That address is for comments about paperwork requirements, not Part B enrollment applications. The signature, witness, submission, and clearance-office instructions are stated on the official CMS-40B form.

Eligible applicants ending employer group coverage may instead use Social Security’s online Part B-only process. Whichever route you use, keeping a complete copy and proof of fax transmission, mailing, delivery, or online submission is a practical recordkeeping precaution, not an additional filing requirement.

For official help, call Social Security at 1-800-772-1213 or TTY 1-800-325-0778. Free personalized counseling is also available through the State Health Insurance Assistance Program. These help options and local-office submission instructions appear on the official CMS-40B page.

This guide provides general educational information. Social Security determines eligibility, effective dates, acceptable supporting evidence, and whether a late-enrollment penalty applies.

Frequently asked questions

How long does CMS estimate it takes to complete Form CMS-40B?

The form’s federal paperwork notice estimates an average completion time of 15 minutes. That estimate covers CMS-40B itself. Gathering employment records, obtaining an employer-completed CMS-L564, resolving missing information, and preparing supporting documents may take additional time.

To complete the process, verify that the applicant already has Part A, download the current CMS-40B, complete every applicable field, attach CMS-L564 or other requested documents, sign and date the form, and submit the complete package to the correct Social Security office. Take unresolved questions about Medicare numbers, qualifying employer coverage, effective dates, penalties, or unavailable employer verification to Social Security or SHIP.