Cracking the Calendar Code
On September 16, 2025, math left us a little puzzle gift. Want to play? Maybe it’s not an official holiday, but in my opinion it should be. Rather than just telling you about the date, I’ll share one of my favorite pattern-finding games—it gives some really interesting answers.
Math is all about pattern recognition. Previously on Talking Math, Amy described number sense as the “relationship between the math and our reasoning.” I think of number sense like phonemic awareness in reading—the skills that help you decode and understand words. In math, number sense includes things like understanding quantity, relationships, decomposition, estimation, and how these ideas connect to the real world.
My favorite way to build number sense with my children is through pattern recognition. Patterns appear in all parts of number sense, and there are endless examples around us every day. So let’s pull out of the fine print and play What Day Is It?
What Day Is It is a fabulous game where you pick any date and describe it in a nontraditional way.
For example, if the date is July 9, 2011, you’re working with the numbers 7, 9, and 2011 (or just 11). Possible answers could be:
Smallest to Largest Day (7 < 9 < 11)
Odd Day
X+2 Day
Here’s another one. Since I’ve been comparing math and reading, let’s try May 6, 1895:
Júlio César de Mello e Souza’s Birthday
Reflection Day (56 → 95)
Palindrome Day (56 + 95 = 151)
There are no wrong answers in this game—every connection has value. And if you don’t understand a connection someone else makes, just ask them to explain. (That’s a whole bonus skill to practice!)
When you get stuck, I recommend starting with observations and allowing them to build to questions, which can lead to additional observations.
“July has 4 letters and it is the 7th month. Being the 7th month means it is more than halfway through a year. Look, you are more than halfway through your dinner. What else can you see 4 of?”
If you want to change things up, you can also play a variation called Year Equation, where you use only the digits of the month and day to equal the year.
May 4, 1984 could be 45x45-45+4=1984
So, what do you notice about 9/16/25?
