CBS4 FOOTBALL BLITZ: Broncos LB Shane Ray is the guest for tonight's taping at Viewhouse Centennial (More Info)

Conception Calculator: How to Estimate the Date You Were Conceived—And What Was Happening 9 Months Prior

By Sam McPherson

We have all been there in our conversations with family and friends, thinking about birthdays and why we have them when we do. Many children have September birthdays, according to data sets from 1973-2014, while very few children have birthdays around Dec. 25 and Jan. 1, as well as other holidays like Halloween and Thanksgiving.

Better Birth Plans

Many couples plan the birth of their child as much as they can, with modern science at their disposal. More than ever, we can potentially even choose now when we want our children to celebrate their birthdays, thanks to modern medicine. However, not all pregnancies are planned this way, and that leaves us with some fun conjecture about just what our parents were doing nine months before our birth dates.

December Holidays Lead To September Birthdays

In the most recent data set from the U.S. National Center for Health Statistics (1994-2003) and the U.S. Social Security Administration (2004-2014), for example, the fourth-most common birthday in the United States is Sept. 17, which puts the conception date roughly on Christmas Day. It’s fun—or scary?—to imagine couples doing their thing together after opening presents under the tree.

Likewise, Sept. 16 is the ninth-most frequent birthday in America, with a projected conception date of Dec. 24. It’s easy to see how a little egg nog might have gotten a lot of parents “in the mood” on Christmas Eve, resulting in a baby delivery 266 days later in the middle of September. We can imagine the same with the conception dates of Dec. 31 and Jan. 1—and their respective birth dates of Sept. 23 (14th overall) and Sept. 24 (17th) in proper context.

Does Valentine’s Day Create a Baby Boom 9 Months Later?

Surprisingly, the conception date of Feb. 14 comes in at just the 120th most-common birthday (Nov. 7). However, due to the range of delivery dates, this isn’t concretely accurate. November birthdays as a whole are not common, with the major holiday looming toward the end of the month. The most-popular November birthday actually is Nov. 21, and that ranked just 80th on the list with an approximate conception date of Feb. 28.

Could May Flowers Bring Baby Showers?

Early February birthdays could suggest a Mother’s Day conception date, but this hasn’t been a prevalent pattern. Valentine’s Day itself is the most-common birth date for the second month (with a May 24 conception estimate), but it ranks just 63rd overall. The next most-frequent birthday in February is the 15th day of the month, which puts it at number 150 in terms of “popularity” on the data chart.

In the end, more and more these days, couples are planning the birth dates of their children more carefully, although every one of us will have a different story to tell about our own birthdays. For older generations, contraception was less readily available, leaving more birth dates to randomness. That just isn’t the case anymore, as the data demonstrates with the dominant birthday season of September every fall as a carefully planned event.

However, it’s always a fun conversation starter at any cocktail or dinner party, to go around the table and have each person think aloud to what may have been significant in the lives of their parents about nine months before they were born. It’s guaranteed to bring out a few chuckles and laughs for a fun social icebreaker in any gathering of family and friends.

Note: The writer’s birthday is July 12, and his mother’s birthday is Oct. 2. There are 282 days between these two dates. Draw your own conclusions.

More From CBS Denver

Weather App
Future Leaders
Together 4 Colorado

Watch & Listen LIVE