How to calculate the due date

The method for calculating the expected delivery date starts from the first day of the last menstrual period: add 9 to or subtract 3 from the month, and add 7 to the date. This gives the estimated due date. A detailed explanation is as follows:

The expected delivery date refers to the approximate time range when the baby will be born. Since pregnant women cannot accurately determine the exact time of conception, according to medical standards, the due date is calculated based on the first day of the last menstrual period. If menstruation is regular, add 9 or subtract 3 from the month and add 7 to the date. For example, if the first day of the last menstrual period was January 1st, the expected delivery date would be October 8th. However, if a woman's menstrual cycle is irregular, this method may not be accurate. In such cases, an ultrasound examination at the hospital can help confirm gestational age more precisely, thus determining a more accurate due date. If there is a significant discrepancy—more than 7 days—between the gestational age calculated from the ultrasound and that derived from the last menstrual period, the ultrasound-based estimate should be used to determine the due date.

Additionally, because ovulation times vary among women and conception dates differ accordingly, the expected delivery date is only an approximation. Any delivery occurring between 37 and 42 weeks of pregnancy is considered full-term, meaning the fetus is fully developed and ready for birth at any point within this period.