For those turning 65, when does Medicare start?

That depends on when an individual signs up for Medicare.  Here are different scenarios. 

• Enroll during the first three months of the Initial Enrollment Period and Medicare starts on the first day of the month of the 65^th birthday. (The Initial Enrollment Period begins three months before the birth month and ends seven months later.)
• Enroll during the month of the 65^th birthday or the three months after it and coverage begins the first day of the next month.

William and Ron both had birthdays in July. William enrolled in Medicare during the month of his birthday and his coverage started in August, one month after his birthday. Ron waited until October and his coverage began in November. There was no late enrollment penalty in these cases.

• For those born on the first day of the month, the Initial Enrollment Period moves up one month. It begins four months before and ends two months after the birth month. Enroll in the first three months and Medicare takes effect the month before the birth month. If enrolling in the last four months, Medicare begins the next month. 
• Miss the Initial Enrollment Period and the next chance to sign up is during the General Enrollment Period from January 1 through March 31 of the next year. Coverage will begin the first day of the month after enrolling and there may be penalties for enrolling late.