If you get your period on the 9th, your menstrual cycle will last 28 days starting on the 9th. Based on the calendar and your doctor's advice, you can calculate your ovulation date.

- Cycle days: starting from the 9th and ending on the next 9th, if your cycle is 28 days, then your cycle is 28 days.

- Subtract 14 days from the number of cycle days: Subtract 14 days from 28 days to get 14 days, which means that the 14th day of your menstrual cycle is the ovulation period.

- Subtract 7 days from the number of days in your cycle: Subtract 7 days from 28 days to get 11 days, which means that the 11th day of your menstrual cycle is the ovulation period.

Therefore, if you have your period on the 9th, then from the 9th to the next 9th, your menstrual cycle will be 28 days, and your ovulation period will be 14 days after the number of cycle days minus 14 days, and the number of cycle days minus 7 A day is a day of 11 days.