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A conception calculator estimates the date of conception based on a known due date or last menstrual period (LMP). Conception typically occurs 14 days after the LMP in a 28-day cycle, about the time of ovulation.

Trinn-for-trinn guide

1. 1From LMP: conception = LMP + ~14 days (ovulation day)
2. 2From due date: conception ≈ due date − 266 days (38 weeks)
3. 3From due date (Naegele): LMP = due date − 280 days, then add 14
4. 4Early ultrasound (6–10 weeks) gives the most accurate conception date estimate

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