Pregnancy Due Date Calculator (Estimate EDD)

Understanding Your Estimated Due Date (EDD)

Your Estimated Due Date (EDD) is the projected date your baby will be born. While exciting, it's important to remember it's just an estimate. Most pregnancies last between 37 and 42 weeks, and only a small percentage of babies arrive exactly on their EDD.

How Due Dates Are Calculated

Several methods estimate the EDD:

• Last Menstrual Period (LMP): The most common method uses Naegele's Rule: Add 7 days to the first day of your LMP, subtract 3 months, and add 1 year. This assumes a standard 28-day cycle with ovulation on day 14.
• Conception Date: If the exact date of conception is known (less common), the EDD is estimated by adding 266 days (38 weeks).
• Ultrasound Dating: Early pregnancy ultrasounds measure the baby's size (like crown-rump length) to determine gestational age, which can then be used to calculate a more precise EDD. Ultrasounds in the first trimester are generally considered the most accurate dating method.

Your doctor will use this information to determine the most likely due date.

Factors Affecting Due Date Accuracy

The accuracy of LMP-based calculations depends on having regular 28-day cycles. Irregular cycles or uncertainty about the LMP date can make this method less precise. Conception date accuracy depends on knowing exactly when ovulation and fertilization occurred. Ultrasound dating accuracy decreases slightly as the pregnancy progresses. Sometimes, the EDD might be adjusted based on later ultrasounds or fetal development.

What is Gestational Age?

Gestational age is the term used to describe how far along the pregnancy is, measured in weeks from the first day of the LMP. A typical full-term pregnancy is considered 40 weeks gestational age. This calculator also estimates your current gestational age based on today's date and your input, helping you track pregnancy milestones. Remember that fetal age (age from conception) is typically about two weeks less than gestational age.