1. What is the NHS Due Date Calculation?

The NHS due date calculation estimates a pregnant woman's expected delivery date by adding 280 days (40 weeks) to the first day of her last menstrual period (LMP). This is known as Naegele's rule.

2. How Does the Calculator Work?

The calculator uses the standard NHS formula:

Where:

• \( LMP \) — First day of last menstrual period
• \( 280\ days \) — Equivalent to 40 weeks gestation

Explanation: This calculation assumes a regular 28-day menstrual cycle with ovulation occurring on day 14.

3. Importance of Due Date Calculation

Details: An accurate due date helps monitor fetal development, schedule important prenatal tests, and identify potential preterm or post-term pregnancies.

4. Using the Calculator

Tips: Enter the first day of your last menstrual period in the format YYYY-MM-DD. The calculator will add 280 days to this date.

5. Frequently Asked Questions (FAQ)

Q1: How accurate is this calculation?
A: Only about 5% of women deliver on their exact due date. Most deliver within 2 weeks before or after.

Q2: What if my cycles aren't regular?
A: The calculation may be less accurate. An early ultrasound can provide a more precise due date.

Q3: Why 280 days?
A: This represents 40 weeks from LMP, accounting for the typical 2 weeks between LMP and conception.

Q4: Will my due date change?
A: Your midwife may adjust your due date based on early ultrasound measurements.

Q5: What's considered full term?
A: Between 37-42 weeks. Babies born before 37 weeks are preterm, after 42 weeks are post-term.