March 14th. That’s the short answer. If you're just looking for a date to circle on your calendar so you can grab a cheap slice of Costco apple pie or a discounted pizza, there you go.
But honestly? There is a whole lot more "math nerd" drama behind the question of when is pie day than most people realize. It isn't just a random Tuesday or Wednesday where bakeries decide to move inventory. It’s a global collision of ancient geometry, a physicist’s birthday, and a very specific American way of writing dates that makes Europeans roll their eyes.
The 3.14 Connection
We celebrate on March 14 because of how we write the date in the United States: 3/14. These are the first three significant digits of $\pi$ (pi), the mathematical constant representing the ratio of a circle's circumference to its diameter. It doesn't matter if the circle is the size of a wedding ring or the size of the observable universe; that ratio is always roughly 3.14159.
Larry Shaw started this whole thing. In 1988, Shaw was a physicist at the San Francisco Exploratorium. He wanted to make math less intimidating, less of a "blackboard and chalk" nightmare for kids. So, he organized a march around one of the museum's circular spaces and followed it up by eating fruit pies. It was quirky. It was local. By 2009, it became so popular that the U.S. House of Representatives actually passed a non-binding resolution making March 14 National Pi Day.
Does timing really matter?
If you want to be a total perfectionist about it, you don't just celebrate on the day. You celebrate at 1:59 p.m. Why? Because the next digits in the sequence are 1, 5, and 9.
Some people go even deeper. They wait for 1:59:26 p.m. to capture those extra seconds of mathematical precision. It’s a bit much for most of us who just want a snack, but for the STEM community, it’s like New Year’s Eve. In 2015, we had what people called "Super Pi Day." The date was 3/14/15. At 9:26:53 a.m., the date and time perfectly matched the first 10 digits of $\pi$. People lost their minds. That won't happen again for another hundred years, so don't hold your breath for the next one.
The Birthday Guest
You can't talk about when is pie day without mentioning Albert Einstein. He was born on March 14, 1879. It’s a weirdly perfect coincidence. Einstein didn't actually discover $\pi$—the Babylonians and Egyptians were messing around with versions of it thousands of years ago—but having the world's most famous physicist share a birthday with the world's most famous constant is just good marketing for science.
Princeton, New Jersey, where Einstein lived for decades, goes absolutely wild. They have pie-eating contests. They have Einstein look-alike contests. You’ll see grown men in grey wigs and fake mustaches sprinting down the street. It’s chaotic and wonderful.
Then you have Stephen Hawking. He passed away on March 14, 2018. It adds a layer of poignancy to the date for the scientific community. It’s a day of birth, death, and infinite numbers.
When is Pie Day for the rest of the world?
Here is where it gets tricky. If you live in a country that uses the Day/Month/Year format (which is basically everywhere except the U.S.), March 14 is written as 14/3. There is no month 14.
So, do they just skip the party? Not exactly.
Many international mathematicians prefer Pi Approximation Day. This is held on July 22. Why? Because the fraction $22/7$ is a common approximation of $\pi$. In fact, $22/7$ is actually closer to the real value of $\pi$ than 3.14 is. If you want to feel intellectually superior to your American friends, July 22 is your day to shine.
There are others, too:
- Two Pi Day: Also known as Tau Day, held on June 28 (6.28). Tau is $2\pi$, and many mathematicians argue it's a much more useful constant than pi ever was.
- Pi Birthday: Some people celebrate on the 314th day of the year, which usually falls on November 10 (or November 9 in leap years).
Why we even care about a number
You use $\pi$ every single day, even if you haven't looked at a geometry textbook since 10th grade. Your GPS uses it to calculate travel distances. Your car tires are manufactured based on it. Even the way your cell phone processes signal waves relies on the math of circles and oscillations.
$\pi$ is what we call an irrational number. It never ends. It never settles into a repeating pattern. We’ve calculated it to over 100 trillion digits now, thanks to supercomputers and people like Emma Haruka Iwao, a Google Cloud developer who has broken the record multiple times.
Think about that. 100 trillion digits. And we still haven't found the "end" because there isn't one. It’s a literal representation of infinity tucked inside a simple circle. That’s why people get tattoos of the symbol. That's why we bake.
The "Pie" vs. "Pi" confusion
Let's be real: most people are here for the food. The pun is too good to pass up.
When you're looking for when is pie day, you're often looking for the deals. Big chains like Whole Foods, Blaze Pizza, and 7-Eleven have turned this into a "food holiday" similar to National Donut Day.
But there is actually a "National Pie Day" that has nothing to do with math. The American Pie Council (yes, that’s a real thing) established National Pie Day on January 23. They’ve been doing it since the 1970s. It’s meant to be a quiet, mid-winter celebration of comfort food.
Hardly anyone remembers the January one. The March one has gravity. It has the backing of NASA and MIT. It has the Einstein connection.
How to actually celebrate
If you want to do this right, don't just buy a frozen crust and call it a day.
- Bake by the numbers. Use a circular tin. Measure the diameter. If you're feeling particularly nerdy, calculate the area of your pie before you eat it using $A = \pi r^2$.
- Support local bakeries. March is a notoriously slow month for retail and food service before the spring rush hits. Many local spots do "buy one, get one for $3.14" deals.
- The Pi-K run. Many schools and communities host 3.14-mile runs. It’s just slightly longer than a 5K (which is 3.1 miles). It’s a great way to burn off the calories from the slice of lemon meringue you’re going to eat later.
- Learn a few digits. Most people know 3.14159. Try to get to 15 digits. It’s a fun party trick, or at least a way to pass the time in a waiting room.
Misconceptions about the day
People often think $\pi$ is just for "math people." Honestly, that's bunk. The reason we celebrate it is that it's one of the few things in the universe that is absolutely, undeniably true everywhere. Whether you're on Earth or Mars, the ratio of a circle remains the same.
Another misconception? That you have to eat sweet pie. Savory pies—shepherd’s pie, pot pie, pizza—are all fair game. In fact, pizza is the most popular way to celebrate in offices because it’s easier to share than a crumbly cherry tart.
Actionable Steps for the Next Pi Day
Don't let the day sneak up on you. If you want to make the most of it, follow this loose plan:
👉 See also: George Leonard's Mastery: Why Most People Never Actually Get Good at Anything
- Set a Calendar Alert: Put a reminder for March 13th to check your local pizza shop's social media. They usually announce their $3.14 deals a day early.
- The 1:59 Goal: If you're in an office or a classroom, aim to have the pie cut and served exactly at 1:59 p.m. It's a small detail that makes you look like the smartest person in the room.
- Donate: Since it’s a day about circles and "cycles," many people use it to donate to STEM education charities. It’s a way to ensure the next generation of engineers actually knows why that number matters.
- Check the NASA Pi Day Challenge: Every year, NASA’s Jet Propulsion Laboratory puts out a set of math problems that their real engineers solve. It’s a cool way to see how $3.14$ helps us land rovers on other planets.
Knowing when is pie day gives you a weird little anchor in the middle of March. It’s a bridge between the cold of winter and the start of spring. It's half-intellectual, half-delicious, and entirely worth the hype. Whether you’re honoring Einstein or just looking for a cheap lunch, March 14 is the date to keep on your radar.