Estimate a likely conception date from your due date or LMP.
Conception is estimated 14 days after the LMP, or 266 days (280 minus 14) before the due date. ACOG's due date convention is LMP + 280 days and assumes a 28-day cycle with ovulation on day 14 (
ACOG). The intercourse window is the 6-day fertile interval ending on the day of ovulation (
ASRM). This is a calendar-based estimate only. It cannot show when conception actually happened, and it is not evidence of paternity or a method of contraception. Ultrasound dating takes priority.
Calculatr