The Conception Calculator

Born on October 25? Here's When You Were Conceived

Birthdays & conception. Updated . Calculated with the standard pregnancy dating method used by ACOG and the NHS.

If you were born on October 25 and arrived close to your due date, you were most likely conceived around February 1 the year before, in the winter (northern hemisphere).

Conception estimates for a October 25 birthday

Born at 37 weeks (early term)February 22
Born at 40 weeks (on the due date)February 1
Born at 42 weeks (late)January 18
Most likely conception rangeJanuary 18 – February 22
Mother's probable due dateclose to October 25 if born at full term

How the estimate works

A full-term pregnancy lasts about 266 days from conception to birth, or 280 days when counted from the first day of the mother's last period. Subtracting 266 days from a birth date gives the most likely conception day, assuming the baby was born around the due date.

If you were born early, conception was later than February 1; if you were born after your due date, it was earlier. A baby born two weeks early was probably conceived around February 22, while one born two weeks late was probably conceived around January 18.

Getting a more exact answer

If your parents know how many weeks pregnant your mother was when you were born, you can narrow this down. Each week earlier than 40 moves the conception date one week later, and each week past 40 moves it one week earlier.

You can also enter a full date of birth, with the year, into the conception calculator by birth date to get weekdays and the right year.

Conception Calculator by Birth Date: Estimate when someone was conceived from their date of birth.

Open the calculator

This article is general information, not medical advice. Talk to a doctor or midwife about your own pregnancy or fertility.