The due date is the date a pregnant woman predicts before giving birth. According to medical knowledge, we can calculate the expected date of delivery from the ovulation period.

So, how to calculate the due date? From the ovulation period, add 1 day for every 7 days until the target date. For example, if a pregnant woman has a 28-day menstrual cycle, their due date is January 17th.

This calculation is not absolute, as a pregnant woman's menstrual cycle may vary. In addition, the physical condition of the pregnant woman and the doctor's prediction may also affect the estimated due date.

Therefore, if a pregnant woman's menstrual cycle is not 28 days, or if the pregnant woman's physical condition or the doctor's prediction changes, their due date may be different. However, generally speaking, calculating the expected date of delivery from the ovulation period is a more accurate calculation method.