The quick answer
For most people, the best time is during your Initial Enrollment Period — the 7 months around your 65th birthday. If you have coverage from a current employer, you may be able to wait without a penalty.
Your Initial Enrollment Period
It starts 3 months before the month you turn 65 and ends 3 months after. Enrolling in the first 3 months means coverage generally starts on the first day of your birthday month.
Example: If you turn 65 in July, your window runs April 1 – October 31. Sign up by June 30 and coverage usually starts July 1.
If you're already on Social Security
You'll typically be enrolled in Parts A and B automatically. Your card should arrive about 3 months before your birthday month.
If you're still working
With group coverage from current employment (yours or your spouse's), you may be able to delay Part B and enroll later using a Special Enrollment Period. Employer size matters. See the details.
If you miss it
You may need to wait for the General Enrollment Period (January 1 – March 31), with coverage starting the month after you sign up — and you may owe late enrollment penalties.
Is timing different in Arizona?
Medicare enrollment periods are federal, so the timing is the same across the country. What differs in Arizona is the specific Medicare Advantage and Part D plans available in your county and ZIP code.
This page is general educational information, not personal advice. Medicare rules, costs, and plan options change and depend on your situation. For official information, visit Medicare.gov or call 1-800-MEDICARE (1-800-633-4227; TTY 1-877-486-2048).