Estimated due date
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You are
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Trimester
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Conception ≈
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This is an estimate using Naegele's rule (LMP + 280 days, adjusted for cycle length). Only about 1 in 20 babies arrive exactly on the due date. An ultrasound dating scan and your doctor give the most reliable dates.
How the due date is worked out
Pregnancy is dated from the first day of your last menstrual period (LMP). The estimated due date is 280 days (40 weeks) later, adjusted if your cycle isn't 28 days. Conception is roughly 2 weeks after the LMP. Trimesters: 1st (weeks 1–13), 2nd (14–27), 3rd (28–40).
FAQs
LMP + 280 days (40 weeks), adjusted for cycle length — Naegele's rule.
An estimate — most babies arrive within two weeks either side. A dating scan is more precise.