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Pregnancy Due Date Formula:
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The NHS Pregnancy Calculator estimates your due date based on the first day of your last menstrual period (LMP). This follows the standard calculation method used by the UK National Health Service for pregnancy dating.
The calculator uses the standard pregnancy due date formula:
Where:
Explanation: This calculation assumes a regular 28-day menstrual cycle and adds 280 days (40 weeks) to the first day of your last period to estimate when your baby is due.
Details: Accurate due date calculation is essential for proper prenatal care, monitoring fetal development, planning maternity leave, and preparing for delivery. It helps healthcare providers schedule important tests and screenings at the appropriate times during pregnancy.
Tips: Enter the first day of your last menstrual period in the date field. Make sure to use the correct date format and select the exact first day of your last period for the most accurate result.
Q1: How accurate is this due date calculation?
A: This method is accurate for women with regular 28-day cycles. Only about 5% of babies are born on their exact due date, with most arriving within two weeks before or after.
Q2: What if my cycle is longer or shorter than 28 days?
A: If your cycle is regular but not 28 days, your healthcare provider may adjust the due date accordingly. The calculation assumes ovulation occurs on day 14.
Q3: When will I have my dating scan?
A: The NHS typically offers a dating scan between 8-14 weeks of pregnancy, which can provide a more accurate due date based on fetal measurements.
Q4: Can the due date change during pregnancy?
A: Yes, if early ultrasound measurements differ significantly from the LMP-based calculation, your midwife or doctor may adjust your due date.
Q5: What is considered full-term pregnancy?
A: A pregnancy is considered full-term between 37-42 weeks. Babies born before 37 weeks are premature, while those born after 42 weeks are post-term.