Special dates

Certain dates, when written down in figures, have a very interesting appearance. On this page a list of such special date. It is important to note that throughout the world different formats are used to write down dates. Some common formats are:
• month / day / year: English language
• day - month - year: other European languages
• year . month . day: Chinese language
Of course, there is also a choice from the number of digits you chose to represent the day, month and year. Some of these are:
• DD - two digit day of the month number
• (D)D - one or two digit day of the month number
• MM - two digit month number
• (M)M - one or two month number
• YYYY - four digit year number
• YY - two digit year number
• (YYY)Y - one, two, three, or four digit year number
From these many different date formats can be constructed.

Same number dates

These are dates which all use the same number. Some examples are:

Pythagorean triple dates

These are dates, that when the year is written with the last two digits form a Pythagorean triple. Some of these dates are:
• March 4, 2005 (4² + 3² = 5²)
• April 3, 2005 (3² + 4² = 5²)
• July 8, 2010 (8² + 6² = 10²)
• August 6, 2010 (6² + 8² = 10²)
• May 12, 2013 (12² + 5² = 13²)
• December 5, 2013 (5² + 12² = 13²)
• September 12, 2015 (12² + 9² = 15²)
• December 9, 2015 (9² + 12² = 15²)
• August 15, 2017 (15² + 8² = 17²)
• December 16, 2020 (16² + 12² = 20²)
• July 24, 2025 (24² + 7² = 25²)
• November 24, 2026 (24² + 10² = 26²)

Double dates

These are dates which consist of twice the same number.

MM/DD/YYYY and YYYY.MM.DD

All double dates of this form are in the past. The last of dates of this form was:
• December 31, 1231 (12/31/1231 or 1231.12.31)

MM/DD/YY and YY.MM.DD

• November 1, 2010 (11/01/10 or 10.11.01)
• January 10, 2011 (01/10/11 or 11.01.10)
• November 11, 2011 (11/11/11 or 11.11.11)
• January 20, 2012 (01/20/12 or 12.01.20)
• November 21, 2012 (11/21/12 or 12.11.21)
• January 30, 2013 (01/30/13 or 13.01.30)
• December 1, 2020 (12/01/20 or 20.12.01)
• February 10, 2021 (02/10/21 or 21.02.10)
• December 11, 2021 (12/11/21 or 21.12.11)
• February 20, 2022 (02/20/22 or 22/02/20)
• December 21, 2022 (12/21/22 or 22.12.21)
• December 31, 2023 (12/31/23 or 23.12.31)

DD-MM-YYYY

Double dates of this form, always appear in the first 12 years of the century. There are a total of 257 of these day with the first being January 1, 1001 and the last being December 31, 3112. Some close double dates of these form are:

Sqaure root days

Examples of Square root days are:
• January 1, 2001 (01-01-01)
• February 2, 2004 (02-02-04)
• March 3, 2009 (03-03-09)
• April 4, 2016 (04-04-16)
• May 5, 2025 (05-05-25)

Palindrome dates

A palindrome is a word, number or sentense which reads the same in reverse order. Of course, there are also palindrome dates (when ignoring all separation symbols). Below a number of these dates are given, grouped by their format.

MM/DD/YYYY and YYYY.MM.DD

There are about 31 centuries having palindrome dates of this format. Most of these centuries have twelve palindrome dates, one for each month. There are a total of 331 of such palindrome dates. Some close palindrome dates of this format are:
• ...
• July 31, 1370 (07/31/1370 or 1370.07.31)
• August 31, 1380 (08/31/1380 or 1380.08.31)
• October 2, 2001 (10/02/2001 or 2001.10.02)
• January 2, 2010 (01/02/2010 or 2010.01.02)
• November 2, 2011 (11/02/2011 or 2011.11.02)
• February 2, 2020 (02/02/2020 or 2020.02.02)
• December 2, 2021 (12/02/2021 or 2021.12.02)
• March 2, 2030 (03/02/2030 or 2030.03.02)
• April 2, 2040 (04/02/2040 or 2040.04.02)
• ...

MM/DD/YY

Each century has twentyfour palindrome dates of this format, and they always occur on the eleventh and the twentysecond of the month. Some close palindrome dates of this format are:

DD-MM-YYYY

These kind of palindrome dates only occur in twelve centuries, namely, those starting with 10, 11, 20, 21, 30, 40, 50, 60, 70, 80, and 90. And in each of those ages, they every time occur in the same month. There are a total of 335 of such palindrome dates. Note that these never occur in October, as that would make a 01YY year, however these dates, when written as DD-MM-YYY are still palindrome dates.

DD-MM-YY and YY.MM.DD

With this palindrome the only possible month is November (11). Which means there are 30 of these palindrome date in each century. Some of the close palindrome dates of this format are:

(M)M/(D)D/(YYY)Y

There are a lot of these kind of palindrome dates, especially in the first centuries. Till December 31, 9999, there are 4090 of these kind of palindrome dates, which makes it the most common form of palindrome date (when the year is not abbreviated).
• ...
• July 29, 1927 (7/29/1927)
• August 29, 1928 (8/29/1928)
• September 29, 1929 (9/29/1929)
• January 10, 2011 (1/10/2011)
• February 10, 2012 (2/10/2012)
• March 10, 2013 (3/10/2013)
• April 10, 2014 (4/10/2014)
• May 10, 2015 (5/10/2015)
• June 10, 2016 (6/10/2016)
• July 10, 2017 (7/10/2017)
• August 10, 2018 (8/10/2018)
• September 10, 2018 (9/10/2019)
• January 20, 2021 (1/20/2021)
• February 20, 2022 (2/20/2022)
• March 20, 2023 (3/20/2023)
• April 20, 2024 (4/20/2024)
• May 20, 2025 (5/20/2025)
• June 20, 2026 (6/20/2026)
• July 20, 2027 (7/20/2027)
• August 20, 2028 (8/20/2028)
• September 20, 2029 (9/20/2029)
• January 30, 2031 (1/30/2031)
• ...

(D)D-(M)M-(YYY)Y

Again, there are many of these kind of palindrome dates. 4123 till December 31, 9999, to be precise. As to be expected consequentive palindrome dates of this form, often occur in the same month.
• ...
• September 18, 1981 (18-9-1981)
• September 28, 1982 (28-9-1982)
• September 19, 1991 (19-9-1991)
• September 29, 1992 (29-9-1992)
• October 1, 2011 (1-10-2011)
• October 2, 2012 (2-10-2012)
• October 3, 2013 (3-10-2013)
• October 4, 2014 (4-10-2014)
• October 5, 2015 (5-10-2015)
• October 6, 2016 (6-10-2016)
• October 7, 2017 (7-10-2017)
• October 8, 2018 (8-10-2018)
• October 9, 2018 (9-10-2019)
• ...

(D)D-(M)M-YY and/or YY.(M)M.(D)D

Of course, these also include many DD-MM-YY and YY.MM.DD palindrome dates.
• ...
• November 10, 2001 (10-11-01)
• ...
• November 20, 2002 (20-11-02)
• ...
• November 30, 2003 (30-11-03)
• January 1, 2011 (1-1-11 or 11.1.1)
• January 11, 2011 (11-1-11 or 11.1.11)
• February 11, 2011 (11-2-11 or 11.2.11)
• March 11, 2011 (11-3-11 or 11.3.11)
• April 11, 2011 (11-4-11 or 11.4.11)
• May 11, 2011 (11-5-11 or 11.5.11)
• June 11, 2011 (11-6-11 or 11.6.11)
• July 11, 2011 (11-7-11 or 11.7.11)
• August 11, 2011 (11-8-11 or 11.8.11)
• September 11, 2011 (11-9-11 or 11.9.11)
• November 1, 2011 (1-11-11 or 11.11.1)
• November 11, 2011 (11-11-11 or 11.11.11)
• January 2, 2021 (21.1.2)
• January 12, 2021 (12-1-21 or 21.1.12)
• February 1, 2021 (1-2-21)
• February 12, 2021 (12-2-21 or 21.2.12)
• March 12, 2021 (12-3-21 or 21.3.12)
• April 12, 2021 (12-4-21 or 21.4.12)
• May 12, 2021 (12-5-21 or 21.5.12)
• June 12, 2021 (12-6-21 or 21.6.12)
• July 12, 2021 (12-7-21 or 21.7.12)
• August 12, 2021 (12-8-21 or 21.8.12)
• September 12, 2021 (12-9-21 or 21.9.12)
• November 12, 2021 (12-11-21 or 21.11.12)
• January 22, 2022 (22-1-22 or 22.1.22)
• February 2, 2022 (2-2-22 or 22.2.2)
• February 22, 2022 (22-2-22 or 22.2.22)
• March 22, 2022 (22-3-22 or 22.3.22)
• April 22, 2022 (22-4-22 or 22.4.22)
• May 22, 2022 (22-5-22 or 22.5.22)
• June 22, 2022 (22-6-22 or 22.6.22)
• July 22, 2022 (22-7-22 or 22.7.22)
• August 22, 2022 (22-8-22 or 22.8.22)
• September 22, 2022 (22-9-22 or 22.9.22)
• November 22, 2022 (22-11-22 or 22.11.22)
• February 3, 2023 (3-2-23)
• February 4, 2024 (4-2-24)
• February 5, 2025 (5-2-25)
• February 6, 2026 (6-2-26)
• February 7, 2027 (7-2-27)
• February 8, 2028 (8-2-28)
• February 9, 2029 (9-2-29)
• January 13, 2031 (13-1-31 or 31-1-13)

(M)M/(D)D/YY

Of course, these also include many MM/DD/YY palindrome dates.
• ...
• October 1 - 9, 2001 (10/1/01 - 10/9/01)
• October 11, 2001 (10/11/01)
• October 22, 2001 (10/22/01)
• January 1, 2011 (1/1/11)
• January 10 - 19, 2011 (1/10/11 - 1/19/11)
• November 1 - 9, 2011 (11/1/11 - 11/9/11)
• November 11, 2011 (11/11/11)
• November 22, 2011 (11/22/11)
• February 1, 2012 (2/1/12)
• February 10 - 19, 2012 (2/10/12 - 2/19/12)
• March 1, 2013 (3/1/13)
• March 10 - 19, 2013 (3/10/13 - 3/19/13)
• April 1, 2014 (4/1/14)
• April 10 - 19, 2014 (4/10/14 - 4/19/14)
• May 1, 2015 (5/1/15)
• May 10 - 19, 2017 (5/10/15 - 5/19/15)
• June 1, 2016 (6/1/16)
• June 10 - 19, 2016 (6/10/16 - 6/19/16)
• July 1, 2017 (7/1/17)
• July 10 - 19, 2017 (7/10/17 - 7/19/17)
• August 1, 2018 (8/1/18)
• August 10 - 19, 2018 (8/10/18 - 8/19/18)
• September 1, 2019 (9/1/19)
• September 10 - 19, 2019 (9/10/19 - 9/19/19)
• January 2, 2021 (1/2/21)
• January 20 - 29, 2021 (1/20/21 - 1/29/21)
• December 1 - 9, 2021 (12/1/21 - 12/9/21)
• December 11, 2021 (12/11/21)
• December 22, 2021 (12/22/21)

"Digital" mirror dates

When using the "digital" numbers consisting of seven segments, there are also mirror dates, which read the same in the mirror. These are rather rare, because they can only make use of the digits 0, 2, 5, and 8. (One could also include the digit 1, which in the mirror reads like 1 as well, but then in the wrong place.)

MM/DD/YYYY and YYYY.MM.DD

They are:
• May 5, 2020 (05/05/2020 or 2020.05.05)
• February 5, 2050 (02/05/2050 or 2050.02.05)
• August 5, 2080 (08/05/2080 or 2080.08.05)
• May 25, 2520 (05/25/2520 or 2520.05.25)
• February 25, 2550 (02/25/2550 or 2550.02.25)
• August 25, 2580 (08/25/2580 or 2580.08.25)
• May 2, 5020 (05/02/5020 or 5020.05.02)
• February 2, 5050 (02/02/5050 or 5050.02.02)
• August 2, 5080 (08/02/5080 or 5080.08.02)
• May 22, 5520 (05/22/5520 or 5520.05.22)
• February 22, 5550 (02/22/5550 or 5550.02.22)
• August 22, 5580 (08/22/5580 or 5580.08.22)
• May 8, 8020 (05/08/8020 or 8020.05.08)
• February 8, 8050 (02/08/8050 or 8050.02.08)
• August 8, 8080 (08/08/8080 or 8080.08.08)
• May 28, 8520 (05/28/8520 or 8520.05.28)
• February 28, 8550 (02/28/8550 or 8550.02.28)
• August 28, 8520 (08/28/8580 or 8580.08.28)

DD-MM-YYYY

All mirror dates of this form are:
• May 20, 2005 (20-05-2005). Also a double date
• May 5, 2020 (05-05-2020)
• May 25, 2025 (25-05-2025)
• May 2, 2050 (02-05-2050)
• May 22, 2055 (22-05-2055)
• May 28, 2085 (28-05-2085)
• May 8, 2080 (08-05-2080)
• February 20, 5005 (20-02-5005)
• February 5, 5020 (05-02-5020)
• February 25, 5025 (25-02-5025)
• February 2, 5050 (02-02-5050)
• February 22, 5055 (22-02-5055)
• February 8, 5080 (08-02-5080)
• February 28, 5085 (28-02-5085)
• August 20, 8005 (20-08-8005)
• August 5, 8020 (05-08-8020)
• August 25, 8025 (25-08-8025)
• August 2, 8050 (02-08-8050)
• August 22, 8055 (22-08-8055)
• August 8, 8080 (08-08-8080)
• August 28, 8085 (28-08-8085)

"Digital" rotation dates

When using the "digital" numbers consisting of seven segments, there are also rotation dates, which read the same when rotated over 180°. These are rare, because they can only make use of the digits 0, 2, 5, 6, 8, and 9. (One could also include the digit 1, which in the mirror reads like 1 as well, but then in the wrong place.)

MM/DD/YYYY and YYYY.MM.DD

Some of these are:
• February 2, 2020 (02/02/2020 or 2020-02-02)
• May 2, 2050 (05/02/2050 or 2050-05-02)
• September 2, 2060 (09/02/2060 or 2060-09-02)
• August 2, 2080 (08/02/2080 or 2080-08-02)
• June 2, 2090 (06/02/2090 or 2090-06-02)
• ...

DD-MM-YYYY

The first few are:
• February 20, 2002 (20-02-2002). Also a double date
• February 2, 2020 (02-02-2020)
• February 22, 2022 (22-02-2022)
• February 5, 2050 (05-02-2050)
• February 25, 2052 (25-02-2052)
• February 9, 2060 (09-02-2060)
• February 8, 2080 (08-02-2080)
• February 28, 2082 (28-02-2082)
• February 6, 2090 (06-02-2090)
• February 26, 2092 (26-02-2092)
• ...