Pi Day is observed on March 14 (the 3rd month) since 3, 1, and 4 are the first three significant figures of π, and was first celebrated in the United States.

[1][19] Many pizza and pie restaurants offer discounts, deals, and free products on Pi Day.

[20] Also, some schools hold competitions as to which student can recall pi to the highest number of decimal places.

[21][22] The Massachusetts Institute of Technology has often mailed its application decision letters to prospective students for delivery on Pi Day.

[27] Princeton, New Jersey, hosts numerous events in a combined celebration of Pi Day and Albert Einstein's birthday, which is also March 14.

[28] In 2024, the recreational mathematician Matt Parker and a team of hundreds of volunteers at City of London School spent six days calculating 139 correct digits of pi by hand, in what Parker claimed was "the biggest hand calculation in a century".

The citation highlights Parker's biennial "Pi Day challenges", stating that they have helped to popularize mathematics.