1. What is the Pregnancy Due Date Calculator?

The Pregnancy Due Date Calculator estimates the expected delivery date based on the last menstrual period using the standard Naegele's rule. This method is widely used in clinical practice and follows UpToDate guidelines for pregnancy dating.

2. How Does the Calculator Work?

The calculator uses the standard obstetric formula:

Where:

• \( EDD \) — Estimated Due Date
• \( LMP \) — First day of Last Menstrual Period
• \( 280 \text{ days} \) — Standard pregnancy duration (40 weeks)

Explanation: This calculation assumes a regular 28-day menstrual cycle and ovulation occurring on day 14. The due date represents the estimated date of delivery at 40 weeks gestation.

3. Importance of Due Date Calculation

Details: Accurate due date estimation is crucial for proper prenatal care, monitoring fetal development, scheduling important tests, and determining the optimal time for delivery.

4. Using the Calculator

Tips: Enter the first day of your last menstrual period. Ensure the date is accurate as this forms the basis for all subsequent pregnancy dating and clinical decisions.

5. Frequently Asked Questions (FAQ)

Q1: How accurate is this due date calculation?
A: This method is accurate for women with regular 28-day cycles. Only about 5% of women deliver exactly on their due date, with most delivering within 2 weeks before or after.

Q2: What if my cycles are irregular?
A: For irregular cycles, early ultrasound dating (especially first trimester) provides more accurate gestational age estimation than LMP-based calculation.

Q3: Can the due date change during pregnancy?
A: Yes, if early ultrasound measurements differ significantly from LMP-based dating (typically >5-7 days difference in first trimester), the due date may be adjusted.

Q4: Why is 280 days used instead of 9 months?
A: 280 days equals 40 weeks, which is the standard obstetric definition of full-term pregnancy. Calendar months vary in length, so weeks provide more precise measurement.

Q5: What is considered full-term pregnancy?
A: Full-term is 39 weeks 0 days to 40 weeks 6 days. Early term is 37 weeks 0 days to 38 weeks 6 days, and late term is 41 weeks 0 days to 41 weeks 6 days.