How Is a Due Date Calculated?
The estimated due date (EDD) is calculated using Naegele’s Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a standard 28-day cycle with ovulation on day 14. For longer or shorter cycles, the due date is adjusted accordingly. Only about 5% of babies are born on their exact due date — most arrive within two weeks either side.
Pregnancy Trimesters
Pregnancy is divided into three trimesters. The first trimester (weeks 1–12) is when the foetus develops its major organs and most miscarriages occur. The second trimester (weeks 13–26) is often the most comfortable, with the anatomy scan typically occurring around week 20. The third trimester (weeks 27–40) involves rapid foetal growth and preparation for birth.
When Is a Baby Considered Full Term?
A baby is considered full term at 37–42 weeks. Births before 37 weeks are premature; births after 42 weeks are post-term. Most healthcare providers will recommend induction by 41–42 weeks if labour has not started naturally.