7 Mistakes You Want To Avoid When Enrolling in Medicare Part B

Medicare Part B is one of three crucial parts of Original Medicare. While Medicare Part A covers inpatient hospital care and Medicare Part D covers prescription medication, Medicare Part B helps you pay for preventative care and medically necessary services. Signing up for — and taking advantage of — Medicare Part B is one key element of a stress-free retirement, but the sign-up process itself may feel a little stressful if you've never enrolled in a government program before.

Fortunately, the process can be easier than you think as long as you avoid these seven common mistakes made by first-time Medicare enrollees.

If you applied for Social Security benefits between ages 62 and 64, you're automatically enrolled in Medicare Part A when you turn 65. And if you start receiving Social Security benefits at least four months ahead of your 65th birthday, you'll be enrolled in Medicare Part B automatically as well.

However, if you aren't yet receiving Social Security benefits by the time you turn 65, you need to sign up for Medicare Part B yourself. Missing your enrollment period can have long-lasting financial consequences, so if you're about to turn 65 and don't currently receive Social Security payments, you need to either opt into Part B or provide evidence that you're covered by an employer's health insurance plan.

Unless you've been automatically enrolled in Medicare, you'll have the opportunity to sign up beginning as early as three months before your 65th birthday, and continuing for three months after. If you don't sign up for Medicare Part B during that initial six month enrollment period, you will have to wait until the general Medicare enrollment period, which runs between January 1 and March 31 each year.

However, if you miss your initial enrollment period, you'll be subject to a late penalty once you do eventually sign up for Medicare Part B. The late enrollment fee totals 10% of the Medicare Part B premium for every year you failed to sign up, so $18.50 per year based on the 2025 monthly premium of $185.

Although you're eligible for Medicare Part B once you turn 65, you might not want to sign up for it if you're still working and covered by your employer's healthcare plan. In this case, you need to provide evidence that your employer's health insurance plan is "creditable," meaning it covers at least as many healthcare services as Medicare Part B.

Typically, this means you'll receive a document from your employer that states you're covered by its health insurance. It's then your responsibility to send that document to the Social Security Administration, which you can do via mail, fax, or an in-person visit to your nearest Social Security branch office.

Once you retire and no longer have access to your employer's health insurance, a special eight-month enrollment window will open up in which you can sign up for Medicare Plan B to avoid late-enrollment penalties.

Companies with more than 20 employees are required to continue offering health insurance options to employees regardless of age. While you can choose to switch from your employer's insurance plan to Medicare Part B at age 65, your company can't require you to do so.

However, this isn't the case for businesses with fewer than 20 employees. The law allows these smaller companies to decide if their employees can stay on their company's health insurance plan after age 65 or require them to switch to Medicare instead.

If you're trying to decide whether to switch to Medicare Part B or stick with your company's health plan, make sure you understand ahead of time whether your company gives you the option.

You can use employer-sponsored health insurance as an alternative to Medicare Part B, but you can't do the same thing with COBRA or retiree health insurance. If you're on either of these health insurance plans when you turn 65, you'll need to sign up for Medicare Part B to ensure you have primary health insurance with limited coverage gaps.

While Medicare Part B is pretty comprehensive, it doesn't cover everything. Routine physical exams, dental care, eye care, and long-term care (including nursing home care) are among some of the things that aren't included in Medicare Part B coverage.

A Medigap policy helps you pay for out-of-pocket costs incurred with Medicare Part A and Part B, such as deductibles, copayments, and coinsurance. Medigap policies are sold by private insurance companies, not the government, so you'll want to compare costs to ensure you find the best Medigap plan for you soon after signing up for Medicare Part B.

Signing up for the right Medicare plan correctly and on time can have a big impact on your retirement plan. Luckily, as long as you avoid the mistakes listed here, you can skip unnecessary late fees and penalties while getting the healthcare you need in retirement.

If you're still worried about choosing the right Medicare plan, you can always reach out to a Medicare customer service representative by calling 1-800-MEDICARE. Medicare is complicated, so getting direct help from an expert is often the best way forward.