How to calculate the due date
Apr 24, 2025
Source: Cainiu Health
Dr. Zhang Lu
Introduction
The due date refers to the estimated date of delivery for a pregnant woman. Methods for calculating the due date include the last menstrual period calculation, fetal movement date calculation, basal body temperature curve analysis, date of onset of morning sickness calculation, and ultrasound examination estimation. However, the due date is only an approximate estimate, and the actual delivery date varies from person to person. Pregnant women should maintain a positive and optimistic mindset, follow a balanced diet, and engage in appropriate physical activity in their daily lives.
The due date refers to the estimated date of delivery for a pregnant woman. There are several methods to calculate it, including the last menstrual period method, fetal movement date method, basal body temperature curve method, morning sickness date method, and ultrasound estimation. However, the due date is only an estimate, and the actual delivery date varies from person to person. Detailed explanations are as follows:
1. Last Menstrual Period Method: You need to accurately remember the first day of your last menstrual period. Add 9 months or subtract 3 months from the month of your last menstrual period (if the month is less than 3, add 9; if it is greater than or equal to 3, subtract 3), and then add 7 days to the date of your last menstrual period. The resulting date is the estimated due date.
2. Fetal Movement Date Method: If a pregnant woman forgets the date of her last menstrual period, she can estimate the due date based on the date of first fetal movement. Typically, fetal movement begins around the 18th to 20th week of pregnancy. For first-time mothers, adding 20 weeks to the date of first fetal movement gives the estimated due date, while for women who have given birth before, adding 22 weeks to the date of first fetal movement gives the estimated due date.
3. Basal Body Temperature Curve Method: If a pregnant woman consistently tracks her basal body temperature, she can calculate the due date based on the basal body temperature curve. The last day of the low-temperature phase on the curve is considered the day of ovulation. Adding 264 to 268 days, or 38 weeks, to this ovulation day gives the estimated due date.
4. Morning Sickness Date Method: Morning sickness usually appears around the sixth week of pregnancy. Adding 280 days to the onset date of morning sickness gives the estimated due date. However, this method is relatively less accurate, as there are significant individual differences in morning sickness symptoms.
5. Ultrasound Estimation: For women with irregular menstrual cycles or those who forgot the date of their last menstrual period, ultrasound examination can be used to estimate the due date. Doctors estimate fetal age based on the development of the fetus, including parameters such as biparietal diameter, crown-rump length, and femur length, and then calculate the estimated due date accordingly.
Pregnant women should maintain a positive and optimistic mindset, follow a balanced diet, engage in moderate physical activity, attend regular prenatal checkups, and follow professional medical advice to ensure the health of both mother and baby.
