In the US, September is the busiest time of year to give birth.

In the US, the busiest month of the year for giving birth is September.

Ever wondered how common your birthday is – or if it's just your imagination that there seems to be a lot of birthdays in September?

In 2006, a Harvard University student published data that showed how many babies were born on each date between 1973 and 1999 in the US. It was discovered that December 25, February 29 and January 1 are the least popular days to give birth, while September 16 is the most popular.

It looks like people conceive during all of those Thanksgiving, Christmas and New Year’s parties 

Earlier this month, the data resurfaced, this time in the easier-to-read format of a heat map.

Andy Kriebel, an American who specializes in data visualision, created an interactive chart that uses colours to rank each day of the year in terms of birth numbers – the lighter the day, the fewer births there were; the darker the day, the more popular it was. By hovering the mouse over a day, it gives the ranking as a number.

Kriebel notes, "September clearly has many of the top days (in fact it has all of the top ten), but July and August aren’t far behind. It looks like people conceive during all of those Thanksgiving, Christmas and New Year’s parties."

Christmastime is clearly the quietest time of year, while American public holidays, such as July 4, are similarly unpopular.

Click through to see the interactive birthday chart in action, or see the static version below.

Static birthday chart