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Expected Due Date Formula:
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The expected due date, also known as the estimated date of delivery (EDD), is the predicted date when a pregnant woman is most likely to give birth. It is calculated based on the first day of the last menstrual period (LMP) plus 280 days (40 weeks).
The calculator uses the standard obstetric formula:
Where:
Explanation: This calculation method, known as Naegele's rule, assumes a regular 28-day menstrual cycle and ovulation occurring on day 14.
Details: Accurate due date calculation is essential for proper prenatal care, monitoring fetal development, scheduling important tests, and preparing for delivery. It helps healthcare providers track pregnancy progress and identify potential complications.
Tips: Enter the first day of your last menstrual period in the date field. The calculator will automatically compute your expected due date by adding 280 days (40 weeks) to your LMP date.
Q1: How accurate is the due date calculation?
A: The due date is an estimate. Only about 5% of women deliver exactly on their due date, while most deliver within 2 weeks before or after.
Q2: What if my menstrual cycle is irregular?
A: For women with irregular cycles, an early ultrasound (first trimester) provides a more accurate due date estimation than LMP-based calculation.
Q3: Why 280 days instead of 9 months?
A: Pregnancy is calculated as 40 weeks from LMP, which equals 280 days. This accounts for the fact that conception typically occurs about 2 weeks after LMP.
Q4: Can the due date change during pregnancy?
A: Yes, healthcare providers may adjust the due date based on early ultrasound measurements, especially if there's a significant difference from LMP-based calculation.
Q5: What is Naegele's rule?
A: Naegele's rule is the standard method for calculating due date: take the first day of LMP, add 1 year, subtract 3 months, and add 7 days.