Enrolling in Medicare: How to Apply, Add Part B, Track Your Medicare Number, and Confirm Your Part A and Part B Start Dates
Enrolling in Medicare
Enrolling in Medicare can feel confusing at first, but the process becomes easier when you know where to begin, what information to watch for, and which steps come next. For most people, enrollment in Original Medicare Part A and Part B begins with Social Security, not directly with a private insurance company.
You can start a Medicare application online at SSA.gov, call Social Security, or contact your local Social Security office. After your application is submitted, one of the most important follow-up steps is creating or using your my Social Security account so you can track your application status and look for your Medicare number and your Part A and Part B effective dates.
Step 1: Know When You Should Apply
Most people first become eligible for Medicare at age 65. In many cases, the Initial Enrollment Period begins three months before the month you turn 65, includes your birthday month, and continues for three months after your birthday month. If you are already receiving Social Security benefits before age 65, you may be automatically enrolled in Medicare Part A and Part B.
If you are still working or covered by active employer group health coverage through your own employment or a spouse, your timing may be different. Some people delay Part B because they have current employer coverage. Before delaying Part B, confirm whether your employer coverage allows you to wait without a late enrollment penalty.
Step 2: Start with Social Security
To enroll in Original Medicare Part A and Part B, start with Social Security.
You have three common ways to apply:
Apply online: Go to SSA.gov/Medicare and start the Medicare application.
Call Social Security: You can call Social Security and request help with Medicare enrollment.
Contact a local Social Security office: You can make an appointment or ask how to submit your Medicare enrollment forms.
When applying online, make sure you are using the official Social Security website. If you are not ready to claim Social Security retirement benefits, you can still apply for Medicare only.
Step 3: Decide Whether You Need Part A Only, Part A and Part B, or Part B Later
Some people enroll in both Part A and Part B when they first become eligible. Others enroll in premium-free Part A and delay Part B because they are still covered by active employer group health coverage. This decision matters because Part B has a monthly premium and may have late enrollment penalties if you delay without qualifying coverage.
If you already have Part A and need to add Part B later, Social Security may require specific forms, especially if you are using a Special Enrollment Period after leaving active employer coverage.
The two forms most people should know about are CMS-40B for Part B enrollment and CMS-L564 to verify employer group health coverage when applicable.
Enrolling in Medicare Part B if You Are Leaving Employer Coverage After You Already Have Part A
A common situation is this: you enrolled in Medicare Part A at 65 because it was premium-free, but you delayed Part B because you were still working and had active employer-sponsored group health coverage. When you retire, leave that employer coverage, or lose access to active employer group coverage, you may need to enroll in Medicare Part B.
This is different from applying for Medicare for the first time. If you already have Medicare Part A and only need Part B, you generally use the Part B enrollment process rather than a first-time Medicare application.
Important Part B Reminder
If you already have Part A and want to add Part B, do not wait until the last minute. Your Part B start date can affect when your Medicare Advantage, Medicare Supplement, or Part D coverage can begin.
Forms commonly used when adding Part B after employer coverage
Application for Enrollment in Medicare Part B (Medical Insurance) (CMS-40B):
Use this form if you already have Medicare Part A and want to sign up for Part B. This form asks for your Medicare number, contact information, and the Part B effective date you are requesting.
Request for Employment Information (CMS-L564):
Use this form to show proof of group health plan coverage based on current employment. You typically complete Section A, and the employer completes Section B to verify the employment-based group health coverage.
Supporting proof of employer coverage: If the employer cannot complete CMS-L564, Social Security may accept other proof of group health plan coverage based on current employment. Check with Social Security before assuming an alternative document will be enough.
Action steps if you already have Part A and need Part B
1.Confirm the date your active employer group health coverage will end or the date you want Medicare Part B to begin.
2.Complete the Application for Enrollment in Medicare Part B (Medical Insurance) (CMS-40B).
3.Have your employer complete the Request for Employment Information (CMS-L564), or gather acceptable proof of employer-sponsored group health plan coverage if the employer cannot complete the form.
4.Submit the Part B enrollment request and employer coverage verification to Social Security online, by fax, by mail, or through a local Social Security office, based on the current Social Security instructions.
5.Create or sign in to your my Social Security account so you can watch for your updated Medicare information, Medicare number, and Part B start date.
6.After your Part B is approved, confirm your Part A and Part B effective dates before choosing or changing any additional Medicare coverage.
For many people leaving employer coverage, the CMS-40B and CMS-L564 forms are the key documents that connect the Part B enrollment request with proof that they had qualifying employer-sponsored group health coverage. This is especially important when a person delayed Part B because they were actively working or covered through a spouse who was actively working.
COBRA and retiree coverage are not the same as active employer coverage.
Before relying on COBRA, retiree benefits, or other post-employment coverage to delay Part B, contact Social Security or speak with a Medicare Specialist so you understand the timing and possible penalty issues.
Step 4: Create or Use Your my Social Security Account
After submitting your Medicare application or Part B enrollment request, create or sign in to your my Social Security account. This account is important because it allows you to track your Medicare enrollment status and access important benefit information.
Once your Medicare information is available, your benefit verification letter may show your Medicare number and your Part A and Part B start dates. This can be especially helpful if you are waiting for the physical Medicare card to arrive in the mail.
Step 5: Look for Your Benefit Verification Letter
Your benefit verification letter can be a useful document after your Medicare enrollment has been processed. It may show your Social Security benefit information and list your Medicare number along with your Medicare Part A and Part B effective dates.
Save a copy of this letter or print it for your records. Having your Medicare number and start dates can help you move forward with reviewing Medicare Advantage, Medicare Supplement, and Part D prescription drug plan options.
Step 6: Confirm Your Medicare Start Dates
Before choosing additional Medicare coverage, confirm your Part A and Part B effective dates. These dates matter because they help determine when other coverage can begin. Do not assume your coverage starts on a specific date until you have verified it through Social Security, your benefit verification letter, or your Medicare card.
Step 7: Review Your Next Medicare Coverage Decisions
After you have your Medicare number and effective dates, the next step is deciding how you want to receive your Medicare coverage. You may want to compare Original Medicare with a Medicare Supplement and Part D prescription drug plan, or compare Medicare Advantage plan options available in your ZIP code.
This is where local guidance can be helpful. Your doctors, prescriptions, pharmacies, budget, travel needs, and county of residence can all affect which Medicare option may fit your situation.
Medicare Enrollment Action Steps
Use this simple checklist to guide the enrollment process:
Confirm when you should enroll in Medicare based on your age, employer coverage, and retirement timeline.
Go to SSA.gov/Medicare to start the Medicare application, or contact Social Security by phone or through a local office.
Choose whether you are applying for Part A only, both Part A and Part B, or Part B only after already having Part A.
If you already have Part A and need Part B after employer coverage, complete CMS-40B and obtain CMS-L564 or other acceptable proof of active employer group health coverage.
Create or sign in to your my Social Security account after submitting the application or Part B request.
Track your application status and watch for your Medicare number.
Generate or save your benefit verification letter when Medicare information is available.
Confirm your Part A and Part B start dates before enrolling in additional Medicare coverage.
Review Medicare Advantage, Medicare Supplement, and Part D options based on your doctors, prescriptions, costs, and ZIP code.
Enrolling in Medicare
Enrolling in Medicare can feel confusing at first, but the process becomes easier when you know where to begin, what information to watch for, and which steps come next. For most people, enrollment in Original Medicare Part A and Part B begins with Social Security, not directly with a private insurance company.
You can start a Medicare application online at SSA.gov, call Social Security, or contact your local Social Security office. After your application is submitted, one of the most important follow-up steps is creating or using your my Social Security account so you can track your application status and look for your Medicare number and your Part A and Part B effective dates.
Step 1: Know When You Should Apply
Most people first become eligible for Medicare at age 65. In many cases, the Initial Enrollment Period begins three months before the month you turn 65, includes your birthday month, and continues for three months after your birthday month. If you are already receiving Social Security benefits before age 65, you may be automatically enrolled in Medicare Part A and Part B.
If you are still working or covered by active employer group health coverage through your own employment or a spouse, your timing may be different. Some people delay Part B because they have current employer coverage. Before delaying Part B, confirm whether your employer coverage allows you to wait without a late enrollment penalty.
Step 2: Start with Social Security
To enroll in Original Medicare Part A and Part B, start with Social Security.
You have three common ways to apply:
Apply online: Go to SSA.gov/Medicare and start the Medicare application.
Call Social Security: You can call Social Security and request help with Medicare enrollment.
Contact a local Social Security office: You can make an appointment or ask how to submit your Medicare enrollment forms.
When applying online, make sure you are using the official Social Security website. If you are not ready to claim Social Security retirement benefits, you can still apply for Medicare only.
Step 3: Decide Whether You Need Part A Only, Part A and Part B, or Part B Later
Some people enroll in both Part A and Part B when they first become eligible. Others enroll in premium-free Part A and delay Part B because they are still covered by active employer group health coverage. This decision matters because Part B has a monthly premium and may have late enrollment penalties if you delay without qualifying coverage.
If you already have Part A and need to add Part B later, Social Security may require specific forms, especially if you are using a Special Enrollment Period after leaving active employer coverage.
The two forms most people should know about are CMS-40B for Part B enrollment and CMS-L564 to verify employer group health coverage when applicable.
Enrolling in Medicare Part B if You Are Leaving Employer Coverage After You Already Have Part A
A common situation is this: you enrolled in Medicare Part A at 65 because it was premium-free, but you delayed Part B because you were still working and had active employer-sponsored group health coverage. When you retire, leave that employer coverage, or lose access to active employer group coverage, you may need to enroll in Medicare Part B.
This is different from applying for Medicare for the first time. If you already have Medicare Part A and only need Part B, you generally use the Part B enrollment process rather than a first-time Medicare application.
Important Part B Reminder
If you already have Part A and want to add Part B, do not wait until the last minute. Your Part B start date can affect when your Medicare Advantage, Medicare Supplement, or Part D coverage can begin.
Forms commonly used when adding Part B after employer coverage
Application for Enrollment in Medicare Part B (Medical Insurance) (CMS-40B):
Use this form if you already have Medicare Part A and want to sign up for Part B. This form asks for your Medicare number, contact information, and the Part B effective date you are requesting.
Request for Employment Information (CMS-L564):
Use this form to show proof of group health plan coverage based on current employment. You typically complete Section A, and the employer completes Section B to verify the employment-based group health coverage.
Supporting proof of employer coverage: If the employer cannot complete CMS-L564, Social Security may accept other proof of group health plan coverage based on current employment. Check with Social Security before assuming an alternative document will be enough.
Action steps if you already have Part A and need Part B
1.Confirm the date your active employer group health coverage will end or the date you want Medicare Part B to begin.
2.Complete the Application for Enrollment in Medicare Part B (Medical Insurance) (CMS-40B).
3.Have your employer complete the Request for Employment Information (CMS-L564), or gather acceptable proof of employer-sponsored group health plan coverage if the employer cannot complete the form.
4.Submit the Part B enrollment request and employer coverage verification to Social Security online, by fax, by mail, or through a local Social Security office, based on the current Social Security instructions.
5.Create or sign in to your my Social Security account so you can watch for your updated Medicare information, Medicare number, and Part B start date.
6.After your Part B is approved, confirm your Part A and Part B effective dates before choosing or changing any additional Medicare coverage.
For many people leaving employer coverage, the CMS-40B and CMS-L564 forms are the key documents that connect the Part B enrollment request with proof that they had qualifying employer-sponsored group health coverage. This is especially important when a person delayed Part B because they were actively working or covered through a spouse who was actively working.
COBRA and retiree coverage are not the same as active employer coverage.
Before relying on COBRA, retiree benefits, or other post-employment coverage to delay Part B, contact Social Security or speak with a Medicare Specialist so you understand the timing and possible penalty issues.
Step 4: Create or Use Your my Social Security Account
After submitting your Medicare application or Part B enrollment request, create or sign in to your my Social Security account. This account is important because it allows you to track your Medicare enrollment status and access important benefit information.
Once your Medicare information is available, your benefit verification letter may show your Medicare number and your Part A and Part B start dates. This can be especially helpful if you are waiting for the physical Medicare card to arrive in the mail.
Step 5: Look for Your Benefit Verification Letter
Your benefit verification letter can be a useful document after your Medicare enrollment has been processed. It may show your Social Security benefit information and list your Medicare number along with your Medicare Part A and Part B effective dates.
Save a copy of this letter or print it for your records. Having your Medicare number and start dates can help you move forward with reviewing Medicare Advantage, Medicare Supplement, and Part D prescription drug plan options.
Step 6: Confirm Your Medicare Start Dates
Before choosing additional Medicare coverage, confirm your Part A and Part B effective dates. These dates matter because they help determine when other coverage can begin. Do not assume your coverage starts on a specific date until you have verified it through Social Security, your benefit verification letter, or your Medicare card.
Step 7: Review Your Next Medicare Coverage Decisions
After you have your Medicare number and effective dates, the next step is deciding how you want to receive your Medicare coverage. You may want to compare Original Medicare with a Medicare Supplement and Part D prescription drug plan, or compare Medicare Advantage plan options available in your ZIP code.
This is where local guidance can be helpful. Your doctors, prescriptions, pharmacies, budget, travel needs, and county of residence can all affect which Medicare option may fit your situation.
Medicare Enrollment Action Steps
Use this simple checklist to guide the enrollment process:
Confirm when you should enroll in Medicare based on your age, employer coverage, and retirement timeline.
Go to SSA.gov/Medicare to start the Medicare application, or contact Social Security by phone or through a local office.
Choose whether you are applying for Part A only, both Part A and Part B, or Part B only after already having Part A.
If you already have Part A and need Part B after employer coverage, complete CMS-40B and obtain CMS-L564 or other acceptable proof of active employer group health coverage.
Create or sign in to your my Social Security account after submitting the application or Part B request.
Track your application status and watch for your Medicare number.
Generate or save your benefit verification letter when Medicare information is available.
Confirm your Part A and Part B start dates before enrolling in additional Medicare coverage.
Review Medicare Advantage, Medicare Supplement, and Part D options based on your doctors, prescriptions, costs, and ZIP code.
Frequently Asked Questions
Do I enroll in Medicare through Medicare.gov or SSA.gov?
For Original Medicare Part A and Part B, you generally enroll through Social Security. Medicare.gov is helpful for learning about Medicare and comparing private Medicare plan options after you have Medicare.
Can I apply for Medicare without taking Social Security retirement benefits?
Yes. If you are not ready to claim retirement benefits, you can apply for Medicare only.
Why do I need a my Social Security account?
A my Social Security account helps you track your Medicare status and access your benefit verification letter, which may show your Medicare number and Part A and Part B start dates.
What is the benefit verification letter?
It is an official Social Security letter that can show benefit information. After Medicare information is processed, it may include your Medicare number and Medicare effective dates.
What if I already have Part A and only need Part B?
If you already have Part A and delayed Part B because you had active employer-sponsored group health coverage, you may need to complete CMS-40B for Part B enrollment and CMS-L564 to verify employer group health coverage.
Who completes CMS-L564?
You generally complete Section A, and your employer completes Section B to verify the dates and type of group health plan coverage based on current employment.
What if I am leaving employer coverage and want Part B to start at a specific time?
State the month and year you want Part B coverage to begin in the appropriate remarks or requested effective date area, following Social Security instructions. Confirm the start date once Social Security processes the request.
What happens after I get my Medicare number?
Once you have your Medicare number and effective dates, you can review Medicare Advantage, Medicare Supplement, and Part D options available in your area.
Do I enroll in Medicare through Medicare.gov or SSA.gov?
For Original Medicare Part A and Part B, you generally enroll through Social Security. Medicare.gov is helpful for learning about Medicare and comparing private Medicare plan options after you have Medicare.
Can I apply for Medicare without taking Social Security retirement benefits?
Yes. If you are not ready to claim retirement benefits, you can apply for Medicare only.
Why do I need a my Social Security account?
A my Social Security account helps you track your Medicare status and access your benefit verification letter, which may show your Medicare number and Part A and Part B start dates.
What is the benefit verification letter?
It is an official Social Security letter that can show benefit information. After Medicare information is processed, it may include your Medicare number and Medicare effective dates.
What if I already have Part A and only need Part B?
If you already have Part A and delayed Part B because you had active employer-sponsored group health coverage, you may need to complete CMS-40B for Part B enrollment and CMS-L564 to verify employer group health coverage.
Who completes CMS-L564?
You generally complete Section A, and your employer completes Section B to verify the dates and type of group health plan coverage based on current employment.
What if I am leaving employer coverage and want Part B to start at a specific time?
State the month and year you want Part B coverage to begin in the appropriate remarks or requested effective date area, following Social Security instructions. Confirm the start date once Social Security processes the request.
What happens after I get my Medicare number?
Once you have your Medicare number and effective dates, you can review Medicare Advantage, Medicare Supplement, and Part D options available in your area.
Medicare Creditable Coverage
Employer Coverage, Part B, and Part D Prescription Drug Coverage
Short Summary of Key Points
For Part D, the key question is whether the employer or union prescription drug coverage is creditable, meaning it is
expected to pay, on average, at least as much as standard Medicare drug coverage.
For Part B, the key question is different: whether the person has group health coverage based on current employment and
whether Medicare or the employer plan pays first.
COBRA and retiree coverage are not the same as active employment-based coverage for delaying Part B. Do not wait until
COBRA ends to review Part B enrollment.
If a person goes 63 or more days without Medicare drug coverage or other creditable prescription drug coverage after
becoming eligible, a Part D late enrollment penalty may apply.
Because the Medicare Part D benefit design changed significantly starting in 2025, employers and employees should
review prescription drug coverage carefully each year instead of assuming last year’s coverage is still creditable.
Important Accuracy Correction
The phrase “creditable coverage” is commonly used when discussing Medicare Part D prescription drug
coverage. It should not be used as a shortcut for every Part B decision. For Medicare Part B, the safer
and more accurate explanation is that a person may be able to delay Part B if they have group
health coverage through current employment, usually their own or a spouse’s current job, and the
employer-size rules support that decision. People should confirm this with their benefits administrator
before delaying Part B.
Part B and Part D: Two Different Questions on Creditable Coverage
Employer Coverage, Part B, and Part D Prescription Drug Coverage
Short Summary of Key Points
For Part D, the key question is whether the employer or union prescription drug coverage is creditable, meaning it is
expected to pay, on average, at least as much as standard Medicare drug coverage.
For Part B, the key question is different: whether the person has group health coverage based on current employment and
whether Medicare or the employer plan pays first.
COBRA and retiree coverage are not the same as active employment-based coverage for delaying Part B. Do not wait until
COBRA ends to review Part B enrollment.
If a person goes 63 or more days without Medicare drug coverage or other creditable prescription drug coverage after
becoming eligible, a Part D late enrollment penalty may apply.
Because the Medicare Part D benefit design changed significantly starting in 2025, employers and employees should
review prescription drug coverage carefully each year instead of assuming last year’s coverage is still creditable.
Important Accuracy Correction
The phrase “creditable coverage” is commonly used when discussing Medicare Part D prescription drug
coverage. It should not be used as a shortcut for every Part B decision. For Medicare Part B, the safer
and more accurate explanation is that a person may be able to delay Part B if they have group
health coverage through current employment, usually their own or a spouse’s current job, and the
employer-size rules support that decision. People should confirm this with their benefits administrator
before delaying Part B.
Part B and Part D: Two Different Questions on Creditable Coverage
What Creditable Prescription Drug Coverage Means
Creditable prescription drug coverage is coverage that is expected to pay, on average, at least as
much as standard Medicare drug coverage.
Common examples may include certain employer or union prescription drug plans, TRICARE,
Department of Veterans Affairs coverage, Indian Health Service coverage, and some retiree or
federal employee plans.
Creditable status is plan-specific. A person should not assume coverage is creditable just because it is
connected to an employer or retiree plan.
Why the Annual Notice Matters
Employers, unions, and other plan sponsors that offer prescription drug coverage to Medicareeligible
individuals generally provide a Notice of Creditable Coverage each year, usually by October 15.
The notice tells the person whether the prescription drug coverage is creditable or non-creditable for
Medicare Part D purposes.
People should keep the notice. A Medicare drug plan may ask for proof of prior creditable coverage if
the person enrolls later.
The 63-Day Part D Rule
After the Medicare Initial Enrollment Period, going 63 or more days in a row without Medicare drug
coverage or other creditable prescription drug coverage may trigger a Part D late enrollment penalty.
The Part D penalty is generally charged for as long as the person has Medicare drug coverage.
When creditable prescription drug coverage ends, the person should act quickly and review Medicare
drug coverage options before the 63-day window is missed.
Coverage That Needs Extra Caution
COBRA does not extend the limited time to sign up for Part B. A person should not wait until COBRA
ends to evaluate Part B enrollment.
Retiree coverage may be helpful, but it is not the same as active employment-based group coverage
for Part B Special Enrollment Period purposes.
Marketplace coverage is generally not treated like current employment-based group coverage once a
person is eligible for Medicare.
Drug discount cards and programs that do not provide coverage as good as standard Medicare drug
coverage are not creditable prescription drug coverage.
Why Part D Redesign Makes This a Bigger Issue
Starting in 2025, Medicare Part D was redesigned. The coverage gap was eliminated and Medicare
added a yearly out-of-pocket cap for covered Part D drugs.
In 2026, Medicare Part D has a $2,100 out-of-pocket cap for covered Part D drugs. This changes the
standard Medicare drug benefit that employer and union plans may be compared against.
CMS allowed group health plans to continue using the existing simplified creditable coverage
determination methodology for 2025, and for 2026 only allowed non-RDS group health plans to use
Drug discount cards and programs that do not provide coverage as good as standard Medicare drug
coverage are not creditable prescription drug coverage.
Creditable prescription drug coverage is coverage that is expected to pay, on average, at least as
much as standard Medicare drug coverage.
Common examples may include certain employer or union prescription drug plans, TRICARE,
Department of Veterans Affairs coverage, Indian Health Service coverage, and some retiree or
federal employee plans.
Creditable status is plan-specific. A person should not assume coverage is creditable just because it is
connected to an employer or retiree plan.
Why the Annual Notice Matters
Employers, unions, and other plan sponsors that offer prescription drug coverage to Medicareeligible
individuals generally provide a Notice of Creditable Coverage each year, usually by October 15.
The notice tells the person whether the prescription drug coverage is creditable or non-creditable for
Medicare Part D purposes.
People should keep the notice. A Medicare drug plan may ask for proof of prior creditable coverage if
the person enrolls later.
The 63-Day Part D Rule
After the Medicare Initial Enrollment Period, going 63 or more days in a row without Medicare drug
coverage or other creditable prescription drug coverage may trigger a Part D late enrollment penalty.
The Part D penalty is generally charged for as long as the person has Medicare drug coverage.
When creditable prescription drug coverage ends, the person should act quickly and review Medicare
drug coverage options before the 63-day window is missed.
Coverage That Needs Extra Caution
COBRA does not extend the limited time to sign up for Part B. A person should not wait until COBRA
ends to evaluate Part B enrollment.
Retiree coverage may be helpful, but it is not the same as active employment-based group coverage
for Part B Special Enrollment Period purposes.
Marketplace coverage is generally not treated like current employment-based group coverage once a
person is eligible for Medicare.
Drug discount cards and programs that do not provide coverage as good as standard Medicare drug
coverage are not creditable prescription drug coverage.
Why Part D Redesign Makes This a Bigger Issue
Starting in 2025, Medicare Part D was redesigned. The coverage gap was eliminated and Medicare
added a yearly out-of-pocket cap for covered Part D drugs.
In 2026, Medicare Part D has a $2,100 out-of-pocket cap for covered Part D drugs. This changes the
standard Medicare drug benefit that employer and union plans may be compared against.
CMS allowed group health plans to continue using the existing simplified creditable coverage
determination methodology for 2025, and for 2026 only allowed non-RDS group health plans to use
Drug discount cards and programs that do not provide coverage as good as standard Medicare drug
coverage are not creditable prescription drug coverage.
Final Takeaway
Employer coverage can affect Medicare decisions, but the rules are not one-size-fits-all. The safest
approach is to verify whether the coverage is based on current employment, confirm who pays first, read
the annual creditable coverage notice, and compare employer prescription drug coverage with Medicare
Part D options before delaying enrollment or making a change
Employer coverage can affect Medicare decisions, but the rules are not one-size-fits-all. The safest
approach is to verify whether the coverage is based on current employment, confirm who pays first, read
the annual creditable coverage notice, and compare employer prescription drug coverage with Medicare
Part D options before delaying enrollment or making a change
