Calculation of mid-cycle for a woman is usually done to determine fertility and ovulation. Dr. Roger W. Harms from the Mayo Clinic states that ovulation happens around day 14 of the menstrual cycle. This is the mid-cycle point for a woman with "normal" menstruation, or a 28-day cycle. However, you may have a longer or shorter menstrual cycle, meaning your mid -ycle, or ovulation, point might be earlier or later than day 14.
Track your menstrual periods for three months to accurately determine the length of your cycle. Most women have a 28-day cycle, but some women fluctuate on a monthly basis and can have shorter or longer cycles.
Mark the first day of your menstrual period on the calendar by circling or placing an "X" on the date. This is the start of your cycle.
Mark the beginning of your next menstrual period during the next month. Count the number of days in between. That is the length of one menstrual cycle.
Repeat Steps 2 and 3 over a three-month period to get an average cycle length. Add the sum of your three cycle lengths together and divide the number by three to get your average cycle length. For example, if your monthly cycle lengths are 28, 30 and 29, your average cycle length is 29 days.
Divide your cycle length by two to determine the mid-cycle day. Your mid-cycle day for a 29-day cycle would be day 15 (14.5, rounded up to 15).
Round up or down when calculating your cycle length. For example, in Step 4, the average of those cycles is 28.6, but round up to 29 days.