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Conception Calculator

Estimate conception date from due date

Conception Calculator

Enter conception date to estimate due date.

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.

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Tip: The estimated conception date is useful for determining the father when timing is uncertain, but DNA testing remains the only definitive method for paternity confirmation.

  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
EventTiming from LMP
Last menstrual period (Day 1)Day 0
Ovulation / Conception windowDay 11–17
ImplantationDay 18–25
Pregnancy test positiveDay 28–35
Heartbeat visible (ultrasound)Week 6
End of 1st trimesterWeek 13
Due date (EDD)Week 40

Fun Fact

Only about 4% of babies are born on their exact due date. The average first pregnancy goes 41 weeks and 1 day. The conception date itself is often uncertain — fertilization can occur up to 5 days after intercourse.

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