Medicare guidance
Medicare Enrollment Periods: When to Sign Up or Change Coverage
Choose the path that matches the coverage you need to start or change. Parts A and B, Medicare Advantage, Part D and Medigap do not share one universal enrollment window.

Use the first-time guides for Medicare Parts A and B. Use the working and retirement guides when employer coverage changes that timeline. If you already have Medicare, use the annual, Medicare Advantage Open Enrollment or Special Enrollment Period guides for the specific plan change you are considering.
VA health care, TRICARE For Life and CHAMPVA have distinct Part B and coordination rules. Use the Veterans and Medicare hub before treating military or veterans coverage like an employer plan.
Start Here
First-Time Parts A and B Enrollment
Working, Retiring and Other Coverage
Annual Medicare Advantage and Part D Changes
Special Enrollment Periods and Coverage Events
Medigap Enrollment Is Different
Special and Local Situations
What Determines Your Medicare Timeline?
Will enrollment be automatic?
Your Social Security or Railroad Retirement status can determine whether a card arrives automatically.
Read the automatic enrollment guide →What coverage do you have?
Current-employment group coverage is treated differently from COBRA, retiree or Marketplace coverage.
Compare coverage types →Who pays first?
Employer size and the reason for Medicare eligibility affect coordination.
Review the payer rules →Who else depends on the plan?
A spouse or dependent may need separate coverage when the employee moves to Medicare.
Plan coverage for a spouse →Information to Gather
- Your expected retirement and coverage-end dates.
- Whether coverage is based on current employment.
- The employer’s official Medicare coordination size.
- Your Social Security or Railroad Retirement status.
- Any HSA contributions by you or the employer.
- Doctors, facilities, prescriptions and pharmacies.
- The spouse or dependents who need replacement coverage.
Frequently Asked Questions
When should I begin preparing for Medicare?
Begin at least three months before the desired start date. Six months gives more time when employer coverage, an HSA, retirement or a spouse’s coverage is involved.
Does everyone automatically receive Medicare at 65?
No. Automatic enrollment generally depends on receiving qualifying Social Security or Railroad Retirement benefits before age 65.
Can I delay Medicare because I am still working?
Possibly, when you have qualifying group coverage based on current employment. Employer size and payer order must also be confirmed.
Does COBRA extend my Part B enrollment period?
No. COBRA does not extend the working-aged Part B Special Enrollment Period.
Can Marketplace coverage replace Medicare at 65?
Most people eligible for premium-free Part A should enroll in Medicare and generally lose eligibility for Marketplace financial assistance for their own coverage.
Do I need to stop HSA contributions?
Yes, for Medicare-covered months. Retroactive premium-free Part A can require contributions to stop months before an application.
Can Thompson Medicare Brokerage enroll me in Parts A and B?
No. Social Security or the Railroad Retirement Board handles Parts A and B. We help compare the private Medicare coverage choices that follow.
More Medicare guidance
Related Articles
Sources and Enrollment Resources
Independent Medicare guidance
Build the Enrollment Path Around Your Actual Coverage
Benjamin Thompson can help people in Missouri and Illinois compare the private Medicare options represented by Thompson Medicare Brokerage and organize the questions to take to Social Security, employers, the Marketplace or a tax professional.
Thompson Medicare Brokerage is not connected with or endorsed by the U.S. government or the federal Medicare program. This resource center provides general educational information. Official enrollment, effective-date, coordination and tax decisions depend on the individual situation.