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This Graphic Proves The Most Common Birthdays Aren’t What You Think

As a birthday present to himself and the internet, Apple data visualizer Bo McCready published an original project that shows just how common every birthday was for those born in the first 15 years of this century. He used data from the Social Security Administration and the CDC’s National Center for Health Statistics and displayed it using an interactive chart. It’s very cool.

The y-axis of the chart is the month of the year, with each day broken out on the x-axis. Each box in the grid has a number that describes how the number of births on that date compares to the number of births per day for the entire year, essentially the number of births divided by 365.

If a given day had the exact number of births you would expect if they were equally distributed, it would have a value of 1.0. The boxes are color-coded, with blue dates more common (over 1.0), orange dates less common (under 1.0), and grey dates with birth ratios relative to average (close to 1.0)

You can go ahead and hover over your own birthday to see how likely it is that today’s five- through 20-year-olds share your birthday, but the more interesting aspect of the chart is how it reveals larger trends.

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The large blue region from late June through early October suggests that more women were getting pregnant in the fall and winter. There are certain days that were less likely to be birthdays likely because inducements an C-sections are less likely to be scheduled. Holidays are particularly unpopular; Christmas is the least common birthday, followed by New Year’s Day, Christmas Eve, and the Fourth of July.

Superstition is the likely cause of the 13th of most months being a less common birthday than the 12th and 14th. Additionally, September 11 is noticeably lower than the surrounding days, including the 12th, the most common birthday of the year. That makes a lot of sense, considering that the September 11 attacks occurred in the second of the 15 years of data captured in the graphic.

All in all, it’s a fun, illuminating project. Here’s hoping that for his next birthday (August 11, the 97th most common birthdate) McCready publishes another project that’s just as captivating.