In most cases, Medicare Part B is not required. In fact, no Medicare program is. While adults who turn 65 are eligible to receive Medicare benefits and can sign up for Original Medicare, Medicare Advantage (MA), and Medigap plans, enrollment is not mandatory, although you could receive penalties if you wait too long. 

There may be times when enrolling in Part B may be the smartest move. Part B is optional, but some additional retirement benefits may depend on Part B enrollment, and it may be necessary to avoid late enrollment fees.

In this article, we’ll answer the top questions about Part B enrollment so you can understand what’s required and avoid those late fees.

Is Medicare Part B required for Medicare Advantage plans?

To enroll in an MA plan, you must be enrolled in both Part A (hospital insurance) and Part B (medical insurance). 

Medicare Advantage is an alternative Medicare plan issued by private insurers that combines Parts A (hospital insurance) and B (medical insurance), and sometimes Part D (prescription drug insurance), offering benefits as good as, or often better than, Original Medicare.

While you’re not allowed to have an Original Medicare Part B plan separate from Medicare Advantage, it’s essential to enroll in the benefit before signing up for an MA plan.

Do I need Part B to enroll in Part D?

Adults 65 and older can enroll in Part D plans without first enrolling in Part B. While the two parts work together to provide better coverage for enrollees, Parts B and D aren’t dependent on each other.

To enroll in Part D, adults must be Medicare-eligible and already signed up for either Part A or Part B. If you’ve paid into Social Security and enroll in a $0 premium Part A plan, you can enroll in a Part D plan, even without Part B. 

Do I still need Part B with employer or private coverage?

Part B isn’t required if you have other insurance — specifically if you have creditable coverage. Creditable coverage is most commonly associated with prescription drug plans, but in this case, it refers to any health plan that is as good as or better than Part B coverage. An employer or union-sponsored plan often counts as creditable coverage. And with it, you can delay Part B enrollment.

You can also avoid late enrollment fees with creditable coverage. If and when this coverage ends, enrollees generally have an eight-month window to join Part B, known as the Special Enrollment Period (SEP). However, if you plan to enroll in an MA or Part D plan, the SEP is two months, not eight.

If you sign up for Part B outside of that window, you’ll become responsible for late enrollment penalties. The late enrollment penalty for Part B is an additional 10% for every 12-month period you’re not enrolled. For example, if you wait three years beyond your enrollment period to join Part B, you’ll pay an additional 30% on top of your monthly Part B premiums ($202.90 in 2026) indefinitely. 

Do federal retirees need to enroll in Medicare Part B?

Medicare Part B is not required for federal retirees. Federal retirees have the option of keeping their Federal Employees Health Benefit (FEHB) into retirement if they are eligible. These benefits are flexible and can be used alongside other insurance, including Original Medicare.

While it isn’t mandatory, Original Medicare plays well with FEHB and provides an extra layer of coverage. With both, Medicare becomes your primary insurer (FEHB your secondary), and enrollees can access a wider range of healthcare providers. Plus, many FEHB plans waive Part B out-of-pocket costs and the deductible.

Is Medicare Part B required for military retirees?

Medicare Part B isn’t generally required for military retirees. However, retired uniformed service members who want TRICARE For Life (TFL) coverage must be enrolled in both Part A and Part B.

Retired military personnel who enroll in Original Medicare are automatically enrolled in TFL. As the first payer, Medicare pays its share of approved services before sending the remaining amount to the TFL claims processor. With both, enrollees often have lower out-of-pocket costs, especially if they receive services covered by both Original Medicare and TFL.

All in all, enrolling in Part B is optional, but it may be a wise choice depending on your needs and the plans you want to enroll in. You need to be enrolled in Part B to join Medicare Advantage and TRICARE For Life Plans. You don’t need it for Part D, or if you have creditable coverage, which allows you to delay premium payments without penalty.

If you’re still researching your Medicare options and need additional support, our licensed SmartMatch agents are available to help.