1. What is the NHS LMP-Based Calculator?

The NHS LMP-based pregnancy calculator estimates the due date (EDD) using the last menstrual period (LMP) date plus 280 days. This is the standard method used by the UK National Health Service for calculating estimated delivery dates.

2. How Does the Calculator Work?

The calculator uses the NHS standard 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 with ovulation occurring on day 14. The 280 days represents 40 weeks of gestation.

3. Importance of Due Date Calculation

Details: Accurate due date calculation is essential for proper prenatal care, monitoring fetal development, scheduling screenings, and planning for delivery. It helps healthcare providers track pregnancy progress and identify any potential issues.

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. The calculator will provide your estimated due date and current gestation.

5. Frequently Asked Questions (FAQ)

Q1: What if my cycle is not 28 days?
A: For irregular cycles, the LMP method may be less accurate. An early ultrasound scan can provide more precise dating.

Q2: How accurate is the LMP method?
A: The LMP method is accurate for women with regular cycles. Only about 5% of babies are born exactly on their due date.

Q3: What is Naegele's Rule?
A: This is the traditional method: add 7 days to LMP, then subtract 3 months. Our calculator uses the simpler 280-day method preferred by NHS.

Q4: When should I have my dating scan?
A: NHS typically offers dating scans between 8-14 weeks of pregnancy to confirm the due date.

Q5: Can the due date change?
A: Yes, if early ultrasound measurements differ significantly from LMP-based dates, healthcare providers may adjust the due date.