Pregnancy Conception Calculator

Last Updated on January 29, 2024 by Emma

Our Pregnancy Conception Calculator efficiently estimates your baby’s conception date using your expected due date, last period, or ultrasound date. It calculates the likely day of conception and provides a possible conception window, considering the 3-5 day viability of sperm in a woman’s body.

Related: Pregnancy Calculator

When Did I Get Pregnant?

Lots of women ask themselves when exactly they got pregnant when trying to figure out the first day their pregnancy started.

Last Monthly Period

Doctors usually calculate how far along a pregnancy is from the first day of the mom’s last monthly period. But biologically, the baby wasn’t actually conceived until the egg got fertilized by sperm, which happens at least 10 days after that.

Because there’s a lot of factors around getting pregnant, it’s hard to name an exact date when conception happened. Different ways to estimate conception help figure out a date range.

Due Date

One way is using the due date, which doctors often determine from an ultrasound at a prenatal checkup. With the due date, they can calculate a possible range of conception dates.


Ultrasounds use sound waves to make images showing the fetus and info about the pregnancy. An “obstetric ultrasound” specifically looks at pregnancy progress. It’s a standard prenatal test giving health information about the mom and fetus. Ultrasounds can measure the fetus as early as 5-6 weeks after the woman’s last monthly period. Comparing ultrasound images with period dates helps determine a better idea of how far along the pregnancy is.

Fertilization and Conception

Getting pregnant scientifically has two main steps – fertilization, when the sperm joins the egg, and conception/implantation when the fertilized egg implants into the uterus wall. Some places define conception and fertilization differently, but doctors and federal policies mostly agree implantation is necessary to be considered pregnant.


  1. Pregnancy Conception Calculator – The Pregnancy Conception Calculator estimates the date of conception based on the expected DUE DATE of the pregnancy, LAST PERIOD date, or ULTRASOUND date. The calculator also keeps in mind that sperm can live inside your body for about 3-5 days. So, you could have conceived a few days after you had sex. This tool gives you a range of days when conception might have happened.

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