If I enroll into another Medicare Part D plan, do I need to contact my old Medicare plan and report the change?
Changing Medicare Part D plans · updated Nov 2, 2025
Your old or existing Medicare Part D plan will be automatically contacted when you enroll in a new Part D plan or Medicare Advantage plan.
The coordination of the cancellation of your old plan and the start of your new plan will be handled between Medicare and the Medicare Part D plan providers.
For example: If you are enrolled in a 2025 Humana Medicare Part D plan and join a 2026 Aetna Medicare Part D plan during the Fall annual Open Enrollment Period, you do not need to contact Humana about the change. Humana will be automatically informed that you are now enrolled into a different 2026 prescription drug plan and Humana will cancel your 2025 plan at the end of the year.
Question: When will my new Medicare Part D plan begin?
If you switch plans during the Fall annual Open Enrollment Period or Annual Coordinated Election Period or Annual Enrollment Period (AEP) running from October 15 to December 7 of each year, your old Medicare Part D prescription drug coverage will end on December 31st and your new prescription drug coverage will begin January 1st.
If you are allowed to join a Medicare Part D plan outside of the AEP, by qualifying for a Special Enrollment Period (SEP), your new Medicare Part D plan or Medicare Advantage plan will start or become effective the first day of the month after enrollment.
For example: If you enroll on June 2, your new Medicare Part D plan will start on July 1. Question: Is it possible that I will receive new membership information from both my old and new plan?
Yes. Sometimes when you change Medicare plans you will receive a Member ID from both your old plan and your newly chosen Medicare plan.
Receiving more than one "Welcome to our plan" letters can happen if you enroll into a new Medicare plan late in the AEP (such as on December 6th) - or if there is an internal computer error causing a slight delay when processing your new enrollment. In such a situation, your old Medicare Part D plan may not be notified of your change before January 1 and may still mail you a new Member ID card and "Welcome" Package for the new plan year - and you will also receive a similar mailing of a Member ID card from your newly chosen Medicare Part D plan.
You will not be able to use both prescription drug plans or Medicare Advantage plans at the same time and instead, you should find that the Member ID card from your old Medicare plan is no longer valid.
For example: If you are enrolled in an 2025 Aetna Medicare Part D plan and, on December 6th you enroll in a 2026 Humana Medicare Part D plan, you may receive new 2026 Member IDs or "Welcome" information from both Humana and Aetna. But, only your newly chosen plan -- the 2026 Humana plan -- will be effective starting January 1st, 2026.
Question: How should you avoid any problems or confusion when changing Medicare plans?
Don't wait too long before enrolling in your newly chosen plan. We suggest that if you are changing Medicare Part D or Medicare Advantage plans, please try to complete your enrollment before the last week of the AEP (before December 1 through December 7) and instead, enroll earlier, such as in mid-November, so that your new enrollment application can be processed before December 7th and you will have a smooth transition into your newly chosen Medicare prescription drug plan. Question: How do you find the Medicare Part D or Medicare Advantage plans that are available in your area?
When in doubt, you can always call a Medicare representative at 1-800-633-4227. We also have several online tools to help you get an overview of the Medicare Part D plans in your area. Here are some good ways to find a new plan for next year:
PDP-Finder - Review all stand-alone Medicare Part D plans (PDPs) available in your state or enter search criteria to narrow the plan list.
MA-Finder - Review all Medicare Advantage plans (MAPDs, MAs, and SNPs) available in your state or enter search criteria to narrow the plan list.
PDP-Wizard - This tool provides you with a little guided help finding a stand-alone Medicare Part D plan. Just answer the questions and we will show you Medicare Part D plans generally meeting your needs.