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Naegele's rule: LMP + 280 days (40 weeks). Ultrasound dating in the first trimester (crown-rump length) is most accurate—within ±5 days at 8–12 weeks. Second-trimester scans have ±2-week error. Only 5% of babies arrive on their exact due date; most arrive within 2 weeks. Due dates are estimates; discuss delivery timing with your OB or midwife.
Estimates due date as LMP + 280 days (Naegele-style rule). Your provider may use ultrasound dating instead.
Estimated due date
Thursday, October 8, 2026