Number Buffs, This Year’s Labor Day Is A Perfect Square!
By Aziz Inan
Labor Day is a federal holiday in the United States observed on the first Monday of September to honor the labor movement and the contributions of American workers to the nation’s growth and achievements. This year, Labor Day falls on Monday, September 1, 2025 and remarkably, it carries with it a rare mathematical distinction.
A Perfect Square Holiday
The year 2025 is itself special: it is a perfect square year, since
2025=45×45
Even more astonishing is that this year’s Labor Day date, written numerically as 9/1/2025 (or simply 912025), is also a perfect square:
912025=955×955
Dates like these are called perfect square dates, a term I first introduced in 2009. A perfect square date is one in which the full date number (written without separators) equals a perfect square.
Past Perfect Square Dates
In 2009, two such dates occurred:
- March 5, 2009 (03/05/2009 → 3052009 = 1747 × 1747)
- April 1, 2009 (04/01/2009 → 4012009 = 2003 × 2003)
Perfect square dates are rare. The 19th and 20th centuries each contained only seven. By contrast, the 21st century is abundant with them—39 in the U.S. date format alone.
2025: A Year Overflowing with Perfect Squares
The year 2025 is especially extraordinary because it contains eight perfect square dates—the highest number to occur in any single year this century:
- January 9 — 01/09/2025
- March 22 — 03/22/2025
- April 18 — 04/18/2025
- June 3 — 6/3/2025
- September 1 — 9/1/2025 (Labor Day)
- September 27 — 09/27/2025
- October 9 — 10/9/2025
- October 27 — 10/27/2025
Depending on whether the month and day are single- or double-digit, perfect square dates may appear in six-, seven-, or eight-digit forms. For example, this year’s Labor Day is expressed as 9/1/2025 (six digits) to reveal its square property.
Interestingly, September 1, 2004—written in eight digits as 09/01/2004—was also a perfect square date, since
9012004=3002×3002
But in that year, Labor Day fell on September 6, not September 1.
A Universal Perfect Square Date
Even more striking is that September 1, 2025 is a perfect square date worldwide. In countries using the day/month/year format, the date is written as 01/09/2025, which also equals a perfect square:
1092025=1045×1045
This makes September 1, 2025, a ubiquitous perfect square date—valid in both U.S. and international date notations.
The 21st century will contain 43 perfect square dates in the day/month/year system, six of which occur in 2025:
- 9 January — 9/1/2025
- 6 March — 6/3/2025
- 14 May — 14/5/2025
- 1 September — 01/09/2025
- 10 September — 10/9/2025
- 27 September — 27/09/2025
Among these, three are ubiquitous perfect square dates, valid in both systems:
- January 9, 2025 — U.S.: 01/09/2025 → 1092025 = 1045 × 1045; World: 9/1/2025 → 912025 = 955 × 955
- September 1, 2025 — U.S. Labor Day: 9/1/2025 → 912025 = 955 × 955; World: 01/09/2025 → 1092025 = 1045 × 1045
- September 27, 2025 — a truly rare case, since it is an eight-digit perfect square in both formats:
- U.S.: 09/27/2025 → 9272025 = 3045 × 3045
- World: 27/09/2025 → 27092025 = 5205 × 5205
A Once-in-a-Lifetime Labor Day
This year’s Labor Day is not just a holiday but also a mathematical celebration. A perfect square date falling on Labor Day—and simultaneously valid in both global date systems—is an exceptionally rare event. The next one will not happen anytime soon.
So as you enjoy this year’s holiday, take a moment to marvel at the beautiful alignment of calendars and mathematics that makes Labor Day 2025 truly one of a kind.
(Inan is a professor at the University of Portland, OR)
