You can calculate the time of ovulation within your
cycle by subtracting the length of your
luteal phase from the length of your
cycle. For example, if your cycle is 28 days long and your luteal phase is 12 days long, the ovulation will occur on day 16 of your cycle (28-12=16). The exact time of ovulation may vary within your cycle, because ovulation can be delayed by a number of factors such as stress, illness, diet, or increased physical activity.