Due Date Calculator

A due date calculator is a tool that estimates when a pregnant woman might give birth based on her last menstrual period (LMP), conception date, ultrasound measurements, or IVF transfer date. The due date, also called the estimated date of delivery (EDD), is typically about 40 weeks from the first day of the last menstrual period. This calculator also estimates the conception date, current gestational age, and important milestones throughout the pregnancy.

Based on Last Menstrual Period

This is the most common method, based on Naegele's rule: adding 280 days (40 weeks) to the first day of the last menstrual period. Adjustments are made for cycles that are longer or shorter than the standard 28 days.

$$\text{预产期} = \text{最后月经第一天} + 280\text{天}$$

Based on Conception Date

If the conception date is known, the due date can be calculated by adding 266 days (38 weeks). Conception typically occurs at or within 24 hours after ovulation.

$$\text{预产期} = \text{受孕日期} + 266\text{天}$$

Based on Ultrasound

Early ultrasound measurements can determine fetal size to establish gestational age. First-trimester (before 13 weeks) ultrasounds are generally the most accurate. This method is particularly useful for women who don't recall their last period or have irregular cycles.

Based on IVF Transfer Date

For pregnancies conceived through in vitro fertilization (IVF), the due date can be calculated from the embryo transfer date. Depending on the age of the embryo at transfer (typically 3 or 5 days), the due date is calculated by adding 266 days to the conception date.

$$\text{预产期} = \text{胚胎移植日期} + 266\text{天} - \text{胚胎年龄}$$

Pregnancy is typically divided into three trimesters, each lasting about 13-14 weeks, with different developmental milestones and changes:

First Trimester (0-13 weeks)

From the first day of the last period through the end of week 13. This is the critical period for organ formation, and the mother may experience morning sickness, fatigue, and mood changes.

Second Trimester (14-27 weeks)

From week 14 through week 27. Many women find this the most comfortable trimester, with early symptoms subsiding and energy increasing. The baby continues to grow and develop, and the mother usually begins to feel movement.

Third Trimester (28-40 weeks)

From week 28 until delivery. The baby grows rapidly and prepares for birth. The mother may experience back pain, trouble sleeping, and swollen ankles.

While due date calculators provide reasonable estimates, the following factors may influence the actual delivery date:

• First-time mothers often deliver later than their due date
• Only about 5% of women deliver on their due date, with most delivering within two weeks before or after
• Irregular menstrual cycles can affect calculations based on last period
• Certain medical conditions may lead to early delivery or scheduled delivery