By Christian BrinkleyLicensed NC Insurance Agent, NPN 22217190, NC Life & Health · Updated November 7, 2026 · 3 min read
Turning 65 while you still work raises a timing question, not just a coverage question. Take Part B at 65, or wait until the job ends? The answer turns on the size of your employer and whether its coverage counts as creditable. Get the timing wrong and you can face a late penalty or a gap with no coverage. Here is how to decide.
When should I apply for Medicare?
In general, apply during your Initial Enrollment Period, the seven months around your 65th birthday: the three months before your birthday month, your birthday month, and the three months after. If you are still working and covered by a large employer's plan, you can usually delay Part B without a penalty, and that delay is the exception most people ask about.
The 20-employee rule
The rule turns on employer size. If you work for an employer with 20 or more employees, or your spouse does, the employer plan usually pays first and Medicare pays second. You can delay Part B while that coverage continues, with no late penalty. If the employer has fewer than 20 employees, Medicare pays first, and you should take Part B at 65 even if you keep working. Ask your benefits office which side of the line your employer falls on.
The 8-month Special Enrollment Period
When the job or the employer coverage ends, you get an eight-month Special Enrollment Period to sign up for Part B without a penalty. The clock starts the month after your employment ends or your employer coverage ends, whichever comes first. Coverage starts the month after you sign up. Do not wait until the eighth month: sign up early so there is no gap between the employer plan ending and Medicare starting.
The two forms: CMS-40B and CMS-L564
Social Security asks for two forms. Form CMS-40B is your application for Part B. Form CMS-L564 is the employer's proof that you had creditable group health coverage: your employer fills in the dates and signs it. Send both to Social Security together. If the employer has closed or will not sign, Social Security can accept other proof of coverage, such as pay stubs or a letter from the plan.
What does not count as employer coverage
COBRA and marketplace plans do not count as employer coverage for this rule. If you leave the job and take COBRA, the eight-month window still runs from when the employment ended, not from when COBRA ends. Waiting out COBRA and then signing up can leave you with a late penalty and months without Part B. The same applies to retiree coverage and a spouse's marketplace plan.
A simple timeline
Two months before your 65th birthday, confirm your employer size and whether the plan is creditable. If it is, you can delay Part B and keep the employer plan. When the job ends, get Form CMS-L564 signed, file it with Form CMS-40B, and sign up in the first month of your eight-month window. Then check drug coverage separately, because delaying Part D has its own penalty rules.
Questions people ask me about this
Can I delay Part B while working?
Yes, if you have creditable coverage through an employer with 20 or more employees. You can sign up later during the eight-month Special Enrollment Period without a late penalty. With a smaller employer, take Part B at 65.
What is the Part B late penalty?
If you delay Part B without creditable coverage, you pay an extra 10 percent of the standard premium for every full 12 months you waited. The penalty usually lasts as long as you have Part B.
Do I need Part A while still working?
Most people should take premium-free Part A at 65, but check one thing first: if you contribute to a health savings account, enrolling in any part of Medicare ends your ability to make HSA contributions.
How do I prove I had employer coverage?
Your employer completes Form CMS-L564 with your coverage dates. Send it to Social Security with Form CMS-40B. If the employer cannot sign, other proof such as pay stubs or a plan letter can work.
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