I just saw a post on social media where someone said “Thanks for all of the birthday wishes! Year 32 is off to a great start!” It was their 32nd birthday. Can you spot the error?

As a mathematics enthusiast, my ears and eyes seem to be fine-tuned to mathematical errors in everyday life. Maybe I’m just being “extra” or maybe it’s a “pet-peeve” but I think mathematical literacy and numeracy is important. It may not be a surprise to you that I also almost always notice grammar errors… but please don’t be too harsh with me if you ever notice one in my posts…

I am nearing the age of 27. It is quickly approaching and I even have a “notes” list in my phone of things I am interested in for my birthday. If I were the type to post about my birthday on social media (I’m not the type– you will usually only see math memes on my social media, or the occasional picture of a baked good I created), I would say “Thanks for all of the birthday wishes! Year 28 is off to a great start!”

Did you catch the error in the post yet? When it is someone’s 32nd birthday, they just completed their 32nd year of life, and are then starting their 33rd.

When I am teaching a concept that may seem too abstract I like to show an example with usually smaller, “easier to deal with” numbers to help students focus on the concept and to not get so hung up on the procedure. So, I think a great way to explain the birthday phenomenon in simple terms is to think about your first birthday. When you turn 1, you have completed your first year of life. If a 1 year old had an advanced vocabulary, they wouldn’t be saying “Year 1 is off to a great start!”

So next time you have a birthday, think about this post! Or, next time you see someone post mathematically incorrect birthday business on their social media, you can share this blog post in the comments and become their hero.