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Yellow Pig Day

Mathematics observance on July 17 to celebrate the number 17 and its properties using the yellow pig as a symbolic mascot.

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July 2026

Last updated February 11, 2026 · by the Holiday Calendar Team

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YEARLY DATEJuly 17

OBSERVED INUnited States

CATEGORYSchool

SUBCATEGORYSTEM

ORIGIN

Institutional Initiative

FOUNDING ENTITY

Michael Spivak and David Kelly

FIRST OBSERVED

1960s

HOW THE HOLIDAY CAME TO BE

Mathematicians Michael Spivak and David C. Kelly invented the concept in the 1960s while graduate students at Princeton University. They began obsessively listing the properties of the number 17 and created the yellow pig as a mascot, later institutionalizing the celebration at the Hampshire College Summer Studies in Mathematics.

View Institutional Noticevia hcssim.org

INTRO

Introduction

PHOTO

It's time to celebrate Yellow Pig Day on July 17! This day is all about celebrating the unique and quirky yellow pig that first appeared in a math book in the 1960s. It started as a joke between two mathematicians, but it quickly gained popularity and has been celebrated yearly ever since. Yellow Pigs have become iconic symbols of mathematics and logic, with their simple yet powerful message of "all things are possible". So put on your best yellow outfit, grab your favorite pig-themed accessories, and get ready to have some fun on this special day!

TIMELINE

Yellow Pig Day Timeline

Inception of Yellow Pig

Mathematicians Michael Spivak and David Kelly own inside joke about a "Yellow Pig" with 17 eyelashes during a summer mathematics course becomes a popular, quirky mathematical symbol.

First Yellow Pig Day

Spivak and Kelly, along with their students, celebrate the first informal "Yellow Pig Day", combining their mathematical enthusiasm with adoration for the fictitious animal.

Popularity Among Mathematicians

The celebration starts to gain popularity among mathematicians across the U.S., particularly in college and university mathematics departments.

Recognition in Mathematical Textbooks

The concept of Yellow Pigs becomes more widely recognized in Spivak's comprehensive set of math textbooks titled "Calculus on Manifolds."

Growing Popularity

Yellow Pig Day gains wider popularity reaching beyond academics, with celebrations featuring pig-themed activities, mathematical puzzles, yellow attire and fun.

International Celebration

Celebrated globally, Yellow Pig Day continues to promote the amalgamation of fun and mathematics, honoring the whimsical symbol that marked its birth.

GET INVOLVED

How to Celebrate Yellow Pig Day

Make your own yellow pig

Using construction paper, scissors, glue and markers you can make your own yellow pig! Get creative and see what kind of pig you can make.

SOLVE

Solve puzzles

Break out the math books and start solving puzzles. A great way to celebrate Yellow Pig Day is to challenge yourself with some math puzzles.

CREATE

Create a yellow pig art project

Using the mathematical properties of the yellow pig, create an art project. You could draw a yellow pig using shapes, make a 3D model out of construction paper or create a painting or sculpture.

READ

Read about the history of the yellow pig

The yellow pig has been around for centuries, so why not learn about its history? Look up articles or books about the history of the yellow pig and learn why it's such an important symbol in mathematics.

Share your love of the yellow pig

Spread the joy of Yellow Pig Day to family, friends, and colleagues. Talk about how much the yellow pig means to you and share your favorite facts about it.

WHY THIS DAY MATTERS

Why We Love Yellow Pig Day

It brings people together

On Yellow Pig Day, parents, teachers, students, and everyone else who loves math come together to celebrate its wonders. It's a chance for people to bond over their shared interest in mathematics and have some fun discussing the various aspects of it - from arithmetic and geometry to calculus and probability!

It's a fun way to learn about math

The famous yellow pig of the 17th century is a great and humorous way to help kids understand basic principles of mathematics. By teaching them the basics in an easy, lighthearted and entertaining way, children can find math more engaging and therefore become more involved and interested in it.

It encourages creativity

Yellow Pig Day is the perfect opportunity for kids to get creative with their math. They can create their own puzzles or games inspired by the Yellow Pig, or even make up stories that incorporate basic mathematical principles. This encourages out-of-the-box thinking and allows them to explore math from a different angle.