🤰 Pregnancy Conception Calculator

Conception dating is an estimation based on medical averages. The actual conception date can vary due to factors like cycle irregularity, ovulation timing, and sperm survival. Ultrasound dating in early pregnancy (especially first trimester) provides the most accurate estimation, typically within 5-7 days of accuracy according to WHO guidelines.

Gestational age is calculated from the first day of your last menstrual period (LMP), which is typically about 2 weeks before conception occurs. Conception date refers to when the sperm fertilized the egg. This is why a pregnancy is considered 40 weeks from LMP, but only 38 weeks from conception according to standard obstetric calculations.

It's challenging to pinpoint the exact conception date because sperm can survive in the female reproductive tract for up to 5 days, and the exact ovulation time can vary. The calculator provides the most likely date based on your cycle information and medical averages. First-trimester ultrasound provides the most accurate estimation.

Ultrasound dating measures fetal size and development to estimate gestational age. In the first trimester, crown-rump length provides the most accurate dating (±5-7 days). Later ultrasounds may be less accurate for dating as genetic factors influence fetal size more significantly. The FDA recommends first-trimester ultrasound for the most accurate pregnancy dating.

If your cycle isn't 28 days, use the advanced options to input your average cycle length. The calculator will adjust the conception date estimation accordingly. Women with longer cycles typically ovulate later, while those with shorter cycles ovulate earlier. The WHO notes that cycle lengths between 21-35 days are considered normal.