How to Enroll in Medicare Part A and Part B: IEP vs. GEP
Whether you are turning 65 or missed your first Medicare sign-up window, here is how to enroll through Social Security—and which enrollment period applies.
What are Medicare Part A and Part B?
Part A generally covers inpatient hospital care, qualifying skilled nursing facility care, hospice and certain home health services. Most people qualify for premium-free Part A. Part B generally covers doctors, outpatient services, preventive care and durable medical equipment; most people pay a monthly premium.
Initial Enrollment Period (IEP): your first opportunity
For most people who become eligible at 65, the IEP lasts seven months: the three months before your 65th-birthday month, your birthday month and the three months after. If your birthday is on the first day of a month, Medicare generally shifts this window one month earlier.
How to apply during your IEP
- Check automatic enrollment. If you already receive Social Security or Railroad Retirement Board benefits, you may be automatically enrolled and receive a Medicare card.
- Apply through Social Security if needed. Start at SSA.gov/medicare/sign-up; you can also call 1-800-772-1213 or arrange an appointment at a Social Security office.
- Choose the coverage you need. You may apply for Parts A and B together; eligible people sometimes enroll in premium-free Part A while delaying Part B because of qualifying coverage through current employment.
- Confirm your effective dates. Keep the Medicare confirmation and make sure your other coverage ends at the appropriate time.
For Part B and premium-Part A, applying in the three months before your birthday month usually means coverage starts the first day of the month you turn 65. Applying in your birthday month or the three months after generally means coverage starts the first day of the next month. Premium-free Part A generally starts the month you turn 65.
General Enrollment Period (GEP): if you missed your first window
The GEP runs January 1–March 31 every year. It is for eligible people who missed their IEP and do not qualify for a Special Enrollment Period. You can enroll in Part B and/or Part A if you must pay a Part A premium. Coverage generally begins the first day of the month after enrollment—not July 1 under an older rule.
Already have Part A but need Part B?
- Contact Social Security and say you need to enroll in Part B during the General Enrollment Period.
- Follow SSA's instructions; Form CMS-40B is the Part B enrollment application, which SSA may ask you to submit.
- Confirm SSA received the request before March 31 and verify your coverage start date.
Have neither Part A nor Part B?
Contact Social Security at SSA's Medicare enrollment page or 1-800-772-1213 to apply and confirm your eligibility. Form CMS-40B alone is not an application for Part A. If you qualify for premium-free Part A, you generally can enroll after 65 without waiting for the GEP, although retroactive coverage may affect Health Savings Account contributions.
Can you use a Special Enrollment Period instead?
If you delayed Part B because you or your spouse had qualifying group health coverage based on current employment, you may qualify for a Part B Special Enrollment Period instead of waiting for GEP. SSA may request Form CMS-L564 to verify employer coverage, along with a Part B application. COBRA, retiree insurance and individual Marketplace insurance generally do not provide that same employment-based protection. Confirm your eligibility with SSA before deciding to wait.
What about late enrollment penalties?
Part B's late enrollment penalty is generally 10% of the standard premium for each full 12-month period you could have enrolled but did not, unless an exception applies. For most people, it lasts as long as they have Part B. Premium-Part A has separate penalty rules. There is usually no penalty for delaying premium-free Part A, although HSA timing deserves special attention.
What happens after Parts A and B start?
After you confirm both effective dates, you can compare how to receive your Medicare benefits: Original Medicare with possible Medigap and Part D coverage, or a Medicare Advantage plan if eligible. These plans have their own enrollment and eligibility rules. Read our Medicare Advantage vs. Medicare Supplement guide and Arizona turning-65 checklist before choosing.
Frequently asked questions
Can I sign up for Part B on Medicare.gov?
No. Social Security handles enrollment in Original Medicare Parts A and B; Medicare.gov explains coverage and provides plan-comparison tools.
Is GEP the same as Medicare Advantage Open Enrollment?
No. Both run January 1 through March 31, but GEP is for Original Medicare Part B and premium-Part A enrollment. Medicare Advantage Open Enrollment is a separate window for certain people already in a Medicare Advantage plan.
What if I still work at 65?
Ask your employer's benefits administrator how the group plan coordinates with Medicare, then confirm Part B Special Enrollment Period eligibility with SSA. Do not assume that every employer plan allows a penalty-free delay.
Need help reviewing your Medicare options?
Tripp Insurance Solutions is an independent insurance agency based in Tucson, Arizona. For Medicare-specific assistance, visit our preferred Medicare resource, Tucson Medicare Center, or contact our team. You enroll in Original Medicare Parts A and B through Social Security—not through our agency.
Official sources
Educational information only. Enrollment eligibility and plan availability depend on your circumstances. Tripp Insurance Solutions is not affiliated with or endorsed by Medicare, CMS or the Social Security Administration.