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Note that this article includes some hyperlinked dates whose format is configurable in "Special pages | Preferences". What you see may not be what the author intended.

Related to the classification of a day as a specific calendar date is the format used to express that date. The differing formats of dates are an example of endianness.

Even for any specific calendar system, different formats are used. For example, the following formats all express the same date in the Gregorian calendar:

Little endian forms, starting with the day

This sequence is common to the vast majority of the world's countries, and is used as the accepted international date usage.

16/11/2003, 16.11.2003, 16-11-2003 or 16-11-03

16th of November 2003

16th November 2003

16 November 2003

16 Nov 2003

Big endian forms, starting with the year

This form is consistent with the endianness of the western decimal numbering system, progressing from the highest to the lowest order magnitude.

2003 November 16

2003-11-16: the ISO 8601 International formal standard ordering for dates, often formatted to be especially easily read and sorted by computers. It is used with UTC in the Internet date/time format (see the external link below). This format is also favoured in certain Asian countries, mainly East Asian countries, as well as in most middle and east european countries like Romania or Hungary. The big endian convention is also frequently used in Canada, but all three conventions are used there.

Middle endian forms, starting with the month

This sequence is common to a smaller number of countries.

November 16, 2003

Nov. 16, 2003

11/16/2003, 11-16-2003, 11.16.2003 or 11.16.03

This order is used in the United States and countries with U.S. influence (but the U.S. federal government sometimes uses day, month, year). England originally used day, month, year, then for a short while used month, day, year, and finally reverted to the original form (day, month, year) which was revived around 1900; the USA chose to stick with month, day, year, but did originally use day, month, year as the English did.

Usage issues

The many numerical forms can create confusion when used in international correspondence, particularly when abbreviating the year to its final two digits.

When numbers are used to represent months, a significant amount of confusion can arise from the ambiguity of a date order; especially when the numbers representing the day, month or year are low, it can be impossible to tell which order is being used. This can be clarified by using four digits to represent years, and naming the month; for example, "Feb" instead of "02". Many Internet sites use year/month/day, and those using other conventions often write out the month (9-MAY-2001, MAY 09 2001, etc.) so there is no ambiguity. The ISO 8601 date order, with four-digit years, is specifically chosen to be unambiguous.

The ISO 8601 standard also has the advantage of being language independent and therefore is useful when there may be no language context and a universal application is desired (expiration dating on export products, for example). Another advantage is that a plain text list of dates with this format can be easily sorted by word processors, spreadsheets and other software tools with built-in sorting functions.

At least in the United States, dates are rarely written in purely numerical forms in formal writing.

Mixed units, for example feet and inches, or pounds and ounces, are normally written with the largest unit first, in decreasing order. Numbers are also written in that order, so the digits of 2006 indicate, in order, the millennium, the century within the millennium, the decade within the century, and the year within the decade. The only date order that is consistent with these well established conventions is year-month-day.

An early U.S. Federal Information Processing Standard recommended 2-digit years. This is now widely recognized as a bad idea. Even some U.S. government agencies now use ISO 8601 with 4 digit years .

When transitioning from one date notation to another, people often write both Old Style and New Style dates.

dd/mm/yy (day, month, year)

Using the dd/mm/yy format, the 30th of December 2006 would be written as 30/12/2006.

The dd/mm/yy format is used by:

Albania

Argentina

Australia

Belgium

Belarus

Bolivia

Brazil

Bulgaria

Canada

Chile

Colombia

Czech Republic ()

Denmark (often in the fraction form d/m-y otherwise dd-mm-yyyy or dd-mm-yy)

Dominican Republic

Ecuador

El Salvador

Estonia

Finland (d.m.y)

France

Germany (form “” is still often used; but see below)

Greece

Guyana

Hong Kong (in English)

Iceland

Ireland

India

Israel

Italy

Kenya

Latvia ( is used more often, but official standard is year-month-day)

Macau (in Portuguese & English)

Malaysia

Mexico

Netherlands

New Zealand

Norway (d.m.y; the fraction form d/m-y is common, but incorrect)

Paraguay

Peru

Poland

Portugal

Romania

Russia

Slovakia ()

Slovenia

Spain

Singapore

Sweden (in the fraction form d/m-y, otherwise yyyy-mm-dd)

Switzerland

Thailand (with Buddhist Era instead of Common Era)

Turkey

Ukraine ()

United Kingdom

Uruguay

Venezuela

Note that '9/11' can refer to both 'The fall of the Berlin Wall' on 9 November 1989 and to the 11 September 2001 attacks on the World Trade Center in the USA. Note also, '9/11' in Chile, means the date when dictator Pinochet trows out the legally president the Chilean coup of 1973

Note also that in the United Kingdom, while it is regarded as acceptable, but rare, to write monthname, day, year (as well as the little endian day, monthname, year), this order is unacceptable when written numerically.

yyyy-mm-dd (year, month, day) - the ISO 8601 standard

Using the yyyy-mm-dd format, the 30th of December 2006 would be written as 2006-12-30.

The ISO 8601 standard, yyyy-mm-dd, is used by:

Austria (although the pre-1996 form “” is still often used)

Canada (yyyy-mm-dd) (All 3 main types are used in Canada- in French and in English)

China (yyyy-mm-dd or yyyy年mm月dd日)

Germany (although the pre-1996 form “” is still often used)

Hong Kong (Chinese)

Hungary ()

Japan (but often in the form yyyy年mm月dd日, or as yy年mm月dd日 when using Japanese era year)

Korea YYYY년 MM월 DD일

Latvia (But often is used)

Lithuania (yyyy-mm-dd)

Macau (Chinese)

Nepal

Norway (yyyy-mm-dd)

South Africa (English; "m/d/yy" is a common alternative)

Sweden (yyyy-mm-dd or )

Taiwan

It is often used in scientific, technical or international communication.

Alphabetical ordering advantages

One of the advantages of using the ISO 8601 standard date format is that it when dates in this format are ordered 'alphabetically' this also orders them in date order e.g. -

1998-02-28 (28th February 1998 - earliest date in the list)

1999-03-01 (1st March 1999 - middle date in the list)

2000-01-30 (30th January 2000 - latest date in the list)

Using the MM-DD-YYYY format, alphabetically ordering the files would put them out of date order:

01-30-2000 (30th January 2000 - latest date in the list)

02-28-1998 (28th February 1998 - earliest date in the list)

03-01-1999 (1st March 1999 - middle date in the list)

Using the DD-MM-YYYY format, alphabetically ordering the files would also put them out of date order:

01-03-1999 (1st March 1999 - middle date in the list)

28-02-1999 (28th February 1998 - earliest date in the list)

30-01-2000 (30th January 2000 - latest date in the list)

yyyy-mmm-dd (year, month, day)

Using the yyyy-mmm-dd format, the 30th of December 2006 would be written as 2006-Dec-30.

The yyyy-mmm-dd format is used by:

Canada (as in 2006-JAN-01)

m/d/y (month, day, year)

Using the m/d/y format, the 30th of December 2006 would be written as 12/30/06. Note that leading zeroes in the month and day are often dropped; for example, the 1st of April 2006 would often be written as 4/1/06.

The m/d/y format is used by:

Canada (Although most official documents use the y-m-d format, the m/d/y format is also understood due to influences from the United States.)

Federated States of Micronesia

Palau

Philippines (formerly d/m/y. May still be found in certain contexts)

United States (Although Independence Day is often referred to as "the Fourth of July.")

Day and year only

The U.S. military sometimes uses a system that indicates the year and day, but not the month. For example, "10 December 1999" can be written in some contexts as "1999345", for the 345th day of 1999. This system is most often used on forms.

See also: calendar, time, date-time group, Japanese calendar, Wikibooks:English:Time

Week number used

Companies in Europe often use year, week number and day for planning purposes. Since a week is a fundamental unit for working life, it makes sense. An event in a project can happen, for example, on w43, w0543 or w543 (week 43 year 2005) or even w43-1 (Monday week 43 year 2005). One problem is that week numbering has different standards, for example the ISO week date, not used by the USA.