16 Sep How to Enroll in Medicare Part B After You Turn 65

September 16, 2025 ~ If you're 65 or older and enrolling in Medicare Part B for the first time after turning 65, it's important to understand the process and timing, especially if you delayed enrollment because you had other coverage.

This blog will walk you through when and how to apply for Medicare Part B, what forms are required, and how to avoid costly penalties.

What Is Medicare Part B?

Medicare is government health insurance for people age 65 and older, people under age 65 who’ve been receiving Social Security Disability Insurance benefits for at least 24 months, and people with End-Stage Renal Disease or ALS.

Part B helps cover outpatient care including:

• Doctors’ visits
• Lab tests and X-rays
• Preventive services
• Durable medical equipment
• Some home health services

Medicare Part B is critical for covering most of your medical costs when you are not admitted to a hospital or skilled nursing facility.

Why Would Someone Delay Enrolling in Part B?

Many people delay enrolling in Part B when they first turn 65, because they still have employer-sponsored health insurance, either through their own job, or through a spouse’s job. In that case, you may qualify for a Special Enrollment Period (SEP) and apply for Part B later—without paying a penalty.

Are You Ever Required to Apply for Part B Even Though You Have Employer-Sponsored Health Insurance?

Yes! If your employer-sponsored health insurance plan is offered by an employer with fewer than 20 employees, you must enroll in Part B when you first turn 65. Medicare becomes the primary payer for your health care expenses. If you don’t enroll in Part B, your employer-sponsored health insurance plan may not cover your health care expenses. If you keep your employer-sponsored health insurance, it will be the secondary payer for your health care expenses.

When Can You Apply for Part B After Age 65?

If the employer offering your employer-sponsored health insurance plan has at least 20 employees, you can enroll in Part B at any time that you have creditable employer coverage. You can also sign up during an 8-month SEP that begins whichever of these things happens first:

• The month after your employment ends, OR
• The month after your employer-provided health insurance coverage ends

Can I Use this SEP if I Have COBRA or Other Retiree Coverage?

No! You cannot use this SEP if you have COBRA, retiree health coverage, Veterans Affairs coverage, or individual health coverage (e.g., Marketplace plans.)

When Does Part B Coverage Begin if I Use the SEP?

If you enroll in Part B while you still have employer-sponsored health insurance or during the first full month when you’re no longer in the plan, you can decide whether you want your coverage to start on the first day of the month you enroll or on the first day of any of the following three months.

If you enroll in Part B during any of the remaining seven months of the SEP, your coverage will begin the first day of the month following your enrollment.

What if I miss the SEP?

If you miss this 8-month window, you may have to wait to enroll in Part B until the General Enrollment Period (January 1–March 31) and pay a late enrollment penalty that increases your monthly premium. The Part B late enrollment penalty adds an extra ten percent to your monthly Part B premium for every twelve months you could have signed up for Part B, but didn’t. In most instances, the penalty lasts as long as you have Medicare.

How to Apply for Part B During the SEP

To apply for Part B after turning 65, you'll need to submit two forms to the Social Security Administration (SSA):

1. CMS-40B – Application for Enrollment in Medicare Part B
2. CMS-L564 – Request for Employment Information
   • This form must be completed by your (or your spouse’s) employer to prove you had coverage.
   • If your employer can’t complete this form, you can submit other proof of coverage such as pay stubs showing health insurance deductions or your health insurance card(s).

How to Submit Your Forms

You can submit these forms to the SSA in one of the following ways:

• Online: Use your My Social Security account to upload the forms.
• Fax or mail: Find your local SSA office at www.ssa.gov/locator for contact information.
• In person: Call ahead to schedule an appointment at your local office.

What If You Already Have Medicare Part A?

Many people enroll in Part A (which covers hospital care) at age 65, but delay enrolling in Part B. If that’s your situation, you’ll still need to actively apply for Part B using the steps above.

Need Help?

Understanding Medicare enrollment rules can feel overwhelming. But you don’t have to figure it all out alone.

• Triage Cancer offers free resources to help you navigate Medicare and other health insurance options. Visit our Medicare & Cancer Resources to learn more. You can also register for this fall’s webinar series: What Should I Know About Medicare?
• Free help is available through our one-on-one Legal & Financial Navigation Program
• Contact your State Health Insurance Assistance Program (SHIP); SHIP provides free, unbiased counseling about Medicare. Find your local SHIP using our Resources by Location.