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NHS Pregnancy Due Date Formula:
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The NHS Pregnancy Due Calculator estimates the expected delivery date based on the first day of your last menstrual period (LMP). This calculation follows the standard NHS method of adding 280 days (40 weeks) to the LMP date.
The calculator uses the standard NHS formula:
Where:
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 (EDD).
Details: Accurate due date estimation is crucial for monitoring fetal development, scheduling prenatal appointments, and planning for delivery. It helps healthcare providers track pregnancy progress and identify any potential complications.
Tips: Enter the first day of your last menstrual period in the date field. Ensure the date is accurate for the most reliable estimation. The calculator will also show how many weeks pregnant you are based on the current date.
Q1: How accurate is the LMP method?
A: The LMP method is generally accurate for women with regular cycles. However, early ultrasound dating scans (especially between 8-13 weeks) can provide more precise dating.
Q2: What if I have irregular periods?
A: If you have irregular periods, the LMP method may be less accurate. An early dating ultrasound is recommended for more precise due date calculation.
Q3: Why 280 days/40 weeks?
A: Pregnancy is traditionally calculated as 40 weeks from the first day of the last menstrual period, which accounts for approximately 38 weeks from actual conception.
Q4: Can the due date change?
A: Yes, due dates may be adjusted based on ultrasound measurements, especially if there's a significant difference from the LMP-based calculation.
Q5: What percentage of babies are born on their due date?
A: Only about 5% of babies are born exactly on their due date. Most births occur within two weeks before or after the estimated due date.