Back in the early 2010s, I made a static heatmap showing birthday popularity that got picked up widely – it even made it into Best American Infographics. But the criticism was valid: I'd colored by rank, not actual birth counts, which exaggerated the differences between dates.

A few years later, I rebuilt it with actual birth data from FiveThirtyEight. Better, but still static.

Now I've finally made what I'd consider the "proper" version: fully interactive, responsive, with features I always wanted to add.

What's here:

  • Interactive heatmap (click or select any date to see its rank)
  • Distribution chart showing all 366 days ranked
  • Compare your birthday with a friend's
  • Zodiac sign breakdown (Virgos dominate, unsurprisingly)
  • Famous people who share your birthday

Key findings:

  • Sept. 9 is the most common birthday (conceived around the holidays)
  • Christmas, Christmas Eve, and New Year's Day are the rarest
  • The data is left-skewed: most dates cluster around 11,000 births/day

Built with SvelteKit and D3. Data: CDC NCHS and SSA via FiveThirtyEight (1994-2014).

🔗 birthdayrank.com

Posted by mattstiles

41 comments

  2. I am surprised to learn that my birthdate of Feb 29 is NOT the rarest birthday in the ranks. Crazy.

    Edit: There has to be skewing of the data due to medical intervention.
    Still interesting.

  3. I remember exploring that 2016 version years ago. Nice to encounter the creator out in the wild! And well done on the latest iteration

  4. Very cool. I’m curious, where do you get the data for famous people’s birthdays and how are they selected?

    I would expect Beyonce to be listed as a famous person born on Sept 4th. She’s not listed, and I haven’t a clue who the other folks are (i.e., Anthony D Weiner, Bernard B Kerik, Raymond W Kelly).

    Edit: refined initial question

  6. Apparently mine (Sep 9) isn’t that common, because it happens to be the only date you highlighted with the yellow box.

  8. Just to point out that these maps are very country specific. You can see major holidays/vacation points in a country by subtracting 9 months from points of accumulations for birthdays.

  9. Can you do the same thing but backed up 40 weeks? I don’t care when people are born I want to know when people are fuckin

  10. Nice work.

    I think your next project is figuring out what factors predict these data. Like, statistically.

    Like, July through September are popular due to a seasonal effect.

    Holidays stand out: January 1, December 25. I didn’t suspect October 31 would be in this list. But also in the other direction, February 14.

    Maybe there’s not enough mystery here. But it would be interesting to see if there are any dates that pop out as unusual results after known factors are taken into account. Or, just what the effect is for certain holidays. Like what’s the odds ratio effect of September 11 vs. December 25 (after the seasonal effect is taken into account).

  11. This raises the question, why do you never see this data set as procreation date?

  12. Huh… my birthday is a white square but I know lots of people who have the same birthday. My SIL is also another white square, weird

  13. My birthday ranks 74th. Average conception day is 11/2, but I was born a few days late so I can conclude my parents probably had sex around Halloween, which lines up because Halloween is my mom’s favorite holiday.

    I happen to know people with the second-least common birthday (my neighbor, who is turning 81 on January 1) and the third-least common birthday (my cousin, who turns 8 I believe today). I also know someone whose sister has a Leap Day birthday.

    Additionally, I’m not sure when his exact birthday is, but another cousin of mine (who is brothers with the Christmas Eve birthday cousin) has his birthday around Thanksgiving, which is rare too.

  14. So December end is a very busy time for couples to get hanky-panky — hence September is the most common birthdays?

  15. I always found it funny that I never met anyone with the same birthday as me. It wasn’t until my 24th bday that I finally did, so I was curious how common it is. Turns out it’s literally the most common day. WTF where were they all hiding?!

  16. This was very interesting.

    Is the source just US data? I am in the UK, and it really took me a while to work out why the late November dates were so low, but I realise now that it’s because of Thanksgiving.

    I wonder if including global data would change the common/least common dates significantly.

  17. Where did you take your data from? I think that’s really important in understanding the trends. Can you break it down by country as well?

  18. I notice american holidays in general have few births. Is that just because planned deliveries (like scheduled cesarean sections) is never done on those dates or is there more to it?

    If I’m seeing it right it seems to be more births in the second half of the year. This is in sharp contrast to Sweden where more people are born in the first half the year.

    2001-2022

    https://preview.redd.it/5hl63gfju69g1.png?width=1200&format=png&auto=webp&s=64af91aa1584a19106c88ec3efaf604425609455

    1921-2000 births in the first half of the year was even more common. [Source.](https://www.scb.se/hitta-statistik/redaktionellt/fler-barn-fods-pa-sommaren-an-pa-varen/)

    Warm summer months and summer vacations is probably the reason for the many born in Mars, April and May in Sweden, especially 1921-2000. What is the reason for the many US births from July to September?

  19. I have a request. Can you make the same heat map but offset by the average duration of a pregnancy, to show when babies are made?

  20. So…people are getting it on the most in about the 3 weeks leading up to Christmas.

  21. What’s up with April 13th? I assume the reason the 13s are on the lighter side generally is because 13 is viewed as an unlucky number, but why is April so much lighter than the rest? Is it because some years that can be Easter or Good Friday?

  22. This is a gorgeous data viz/analysis project. I do have a question though: Is there a reason you didn’t include probability as another one of the metrics displayed when we select a date?

  23. I absolutely LOVE this kind of data; it fascinates me. I’ve seen the original map before and this website is awesome! Thank you for organizing all of this and putting it in an easy to use format.

    I’d be curious to see the effect on September 11 as a birthday post-2001. Maybe the 20 years before and after could show it. I can’t imagine many people choose C sections and inductions on 9/11 after 2001.

  24. My birthday of July 1 is stated to be a popular one, but I have yet to meet a single other person who shares it.

  25. It’s crazy that September has the majority of most common birthdays. People be fuckin during the holidays.

  26. Why is 14/2 so common? I’d understand 14/10, the outcome of Valentine’s sex, but surprisingly 14/10 isn’t actually that common. Do people have a lot of sex on 14/5?

  28. that color scheme is not beautiful considering the distribution of the data. seems arbitrary.

    should have the colors change every 10% say.

    there’s a huge variation in the lowest ~75% which is totally not visible

  29. Small suggestion: for January 15th, you should include Martin Luther King Jr. in the list of famous births. His birthday of January 15th actually the reason why January is the month when MLK Day is celebrated — the U.S. federal holiday always on the third Monday in January.

  30. Very cool! 
    It would also be nice to compare between countries, cultures, years, and particular dates.

  33. I’m confused as to why two days right next to each other would have considerably different frequencies

  34. Is it the same pattern in Australia, in the southern hemisphere?

    Explanation: is it that people have sex more in the winter, when the nights are longer, and the weather is foul?

  35. Jesus made sure no one was born on his birthday.

  36. I’m swedish and had a peek just for funsies. conception put me around midsummer – which I imagine would be a very common conception time for my neck of the woods! would be really cool to see comparisons across cultures, if what are the most popular conceptions/birthdays in different parts of the world.

    obviously beyond the scope of what you’ve built here, but fun to think about!

  37. funny how my gfs bday is the 25.12 and mine is the 01.01, probably one of the rarest combinations

  38. So….people be bangin a lot around Christmas. Got it!

  39. This is really interesting. It seem to prove that the body is able to control when a baby comes out (in the last few hours). That or the data is influenced by hospital behaviors around the holidays.

  40. Can the rarity of births on holidays such as 1/1, 7/4, Thanksgiving-ish, and Christmas be attributed to inductions and not scheduling deliveries alone or are woman literally willing their children to not be born on such days?

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