Born on December 18? Here's When You Were Conceived
If you were born on December 18 and arrived close to your due date, you were most likely conceived around March 27 the year before, in the spring (northern hemisphere).
Conception estimates for a December 18 birthday
| Born at 37 weeks (early term) | April 17 |
|---|---|
| Born at 40 weeks (on the due date) | March 27 |
| Born at 42 weeks (late) | March 13 |
| Most likely conception range | March 13 – April 17 |
| Mother's probable due date | close to December 18 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 March 27; if you were born after your due date, it was earlier. A baby born two weeks early was probably conceived around April 17, while one born two weeks late was probably conceived around March 13.
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 calculatorThis article is general information, not medical advice. Talk to a doctor or midwife about your own pregnancy or fertility.