Pregnancy Conception Calculator
This calculator estimates the date of conception — the day the baby was likely conceived — based on your due date, last menstrual period, or ultrasound. It also shows the probable fertile window during which intercourse may have led to conception.
Your Results
| Detail | Date / Range |
|---|---|
| Estimated Conception Date | — |
| Possible Conception Window | — |
| Fertile Window (intercourse may have led to conception) | — |
| Estimated Due Date | — |
| Current Week of Pregnancy | — |
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When Did Conception Happen?
Conception typically occurs around 11-21 days after the first day of the last menstrual period for women with regular cycles. The exact day is hard to determine because sperm can survive inside the body for 3-5 days, and the egg is viable for 12-24 hours after ovulation.
This calculator estimates the most likely conception date and shows a "fertile window" — the range of days during which intercourse could have resulted in pregnancy.
Conception vs. Implantation
Conception (fertilization) is when sperm meets the egg in the fallopian tube. Implantation occurs 6-12 days later when the fertilized egg attaches to the uterine wall. A pregnancy test typically becomes positive around implantation.
Methods Used
From Due Date: Conception ≈ Due Date − 266 days.
From LMP: Conception ≈ LMP + 14 days (adjusted for cycle length).
From Ultrasound: LMP is back-calculated from the ultrasound-measured gestational age, then conception is estimated from that.