Pregnancy Conception Calculator
Estimate the date of conception and the likely window of intercourse based on your due date, last period, or ultrasound.
Fertilization vs. Conception
While often used interchangeably, there is a medical distinction:
- Fertilization: The moment a sperm penetrates the egg. This usually happens in the fallopian tube.
- Conception/Implantation: The moment the fertilized egg (blastocyst) implants itself into the uterine lining, which marks the true beginning of a medical pregnancy. This typically happens 6-10 days after fertilization.
When Did I Conceive?
If you have a regular 28-day cycle, conception typically occurs about 14 days after the first day of your last period. However, cycle lengths vary greatly.
Ultrasound Accuracy
Early ultrasounds (before 13 weeks) are the most accurate way to date a pregnancy. They measure the "Crown-Rump Length" of the fetus to estimate gestational age, which can then be used to back-calculate the likely conception date with high precision (+/- 5-7 days).