1. What is the NHS EDD Calculator?

The NHS EDD (Estimated Due Date) Calculator estimates the expected delivery date based on the last menstrual period using the standard NHS calculation method of adding 280 days to the LMP date.

2. How Does the Calculator Work?

The calculator uses the NHS standard formula:

Where:

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

Explanation: This calculation is based on Naegele's rule and represents the standard method used by the NHS for estimating due dates from the first day of the last menstrual period.

3. Importance of Due Date Calculation

Details: Accurate due date estimation is crucial for monitoring fetal development, scheduling prenatal care, preparing for delivery, and identifying potential pregnancy complications.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: How accurate is the NHS due date calculation?
A: The calculation provides an estimated date - only about 5% of babies are born exactly on their due date. Most births occur within 2 weeks before or after the estimated date.

Q2: What if I don't know my LMP exactly?
A: If LMP is uncertain, an ultrasound scan in early pregnancy (8-14 weeks) can provide a more accurate due date estimation.

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 the LMP.

Q4: Can the due date change during pregnancy?
A: Yes, if early ultrasound measurements differ significantly from the LMP-based calculation, healthcare providers may adjust the due date.

Q5: What if I have irregular periods?
A: For women with irregular cycles, ultrasound dating in the first trimester is more reliable than LMP-based calculations.