Date and time notation in the United States

Date and time notation in the United States differs from that used in nearly all other countries. It is inherited from one historical branch of conventions from the United Kingdom. American styles of notation have also influenced customs of date notation in Canada, creating confusion in international commerce.[1]

In traditional American usage, dates are written in the month–day–year order (e.g. May 24, 2019) with a comma before and after the year if it is not at the end of a sentence,[2] and time in 12-hour notation (7:02 pm).

International date and time formats typically follow the ISO 8601 format (2019-05-24) for all-numeric dates,[3] write the time using the 24-hour clock (19:02),[4] and notate the date using a day–month–year format (24 May 2019).[5] These forms are increasingly common in American professional, academic, technological, military, and other internationally oriented environments.

Date and time notation in the United States
Full dateMay 24, 2019
24 May 2019
All-numeric date05/24/19
Time7:02 pm
19:02 [refresh]


In the United States, dates are traditionally written in the "month-day-year" order, with neither increasing nor decreasing order of significance. This order is used in both the traditional all-numeric date (e.g., "1/21/16" or "01/21/2016") and the expanded form (e.g., "January 21, 2016"—usually spoken with the year as a cardinal number and the day as an ordinal number, e.g., "January twenty-first, twenty sixteen"), with the historical rationale that the year was often of lesser importance. The most commonly used separator in the all-numeric form is the slash (/), although the hyphen (-) and period (.) have also emerged in the all-numeric format recently due to globalization. The Chicago Manual of Style discourages writers from writing all-numeric dates in this format, since it is not comprehensible to readers outside the United States.[5]

The day-month-year order has been increasing in usage since the early 1980s. The month is usually written as an abbreviated name, as in "19 Jul 1922" (sometimes with hyphens).[5] Many genealogical databases and the Modern Language Association citation style use this format. When filling in the Form I-94 cards and new customs declaration cards used for people entering the U.S., passengers are requested to write pertinent dates in the numeric "dd mm yy" format (e.g. "19 07 22"). Visas and passports issued by the U.S. State Department also use the day-month-year order, complying with the international ICAO Convention Travel Document Standards.[6][7]

The fully written "day-month-year" (e.g. 25 August 2006) in written American English is becoming more common outside of the media industry and legal documents, particularly in university publications and in some internationally influenced publications as a means of dealing with ambiguity. The Chicago Manual of Style recommends it for material that requires many full dates, since it does not require commas.[8] Most Americans still write "August 25, 2006" in informal documents. Speaking the "day month year" format is still somewhat rare, with the exception of holidays such as the Fourth of July.

The year-month-day order, such as the ISO 8601 "YYYY-MM-DD" notation is popular in computer applications because it reduces the amount of code needed to resolve and compute dates. It is also commonly used in software cases where there are many separately dated items, such as documents or media, because sorting alphabetically will automatically result in the content being listed chronologically. Switching the U.S.'s traditional date format from month-day-year to year-month-day may be considered less of a break, since it preserves the familiar month-day order.

Two U.S. standards mandate the use of year-month-day formats: ANSI INCITS 30-1997 (R2008); and NIST FIPS PUB 4-2 (FIPS PUB 4-2 withdrawn in United States 2008-09-02[9]), the earliest of which is traceable back to 1968. This order is also used within the Federal Aviation Administration and military because of the need to eliminate ambiguity.

The United States military normally uses the "dd mmm yyyy" format for correspondence. The common month-day-year format is used when corresponding with civilians.[10] The military date notation is similar to the date notation in British English but is read cardinally (e.g. "Nineteen July") rather than ordinally (e.g. "The nineteenth of July").

Weeks are generally referred to by the date of some day within that week (e.g., "the week of May 25"), rather than by a week number. Many holidays and observances are identified relative to the day of the week on which they are fixed, either from the beginning of the month (first, second, etc.) or end (last, and far more rarely penultimate and antepenultimate). For example, Thanksgiving is defined as being on "the fourth Thursday in November". Some such definitions are more complex. For example, election day is defined as "the Tuesday next after the first Monday in the month of November" or "the first Tuesday after November 1".[11] Calendars mostly show Sunday as the first day of the week.


While most countries use the 24-hour clock, the United States differs in that it uses the 12-hour clock almost exclusively, not only in spoken language, but also in writing, even on timetables, for airline tickets, and computer software. The suffixes "a.m." and "p.m." (often represented as AM and PM) are appended universally in written language. Alternatively, people might specify "noon" or "midnight", after or instead of 12:00. (Business events, which are increasingly scheduled using groupware calendar applications, are less vulnerable to such ambiguity, since the software itself can be modified to take care of the naming conventions.) Where the a.m.–p.m. convention is inconvenient typographically (e.g., in dense tables), different fonts or colors are sometimes used instead. The most common usage in transport timetables for air, rail, bus, etc. is to use lightface for a.m. times and boldface for p.m. times.

24-hour usage

The 24-hour clock is used in military and scientific contexts in the United States.[4] It is best known for its use by the military, and therefore commonly called "military time". In U.S. military use, 24-hour time is traditionally written without a colon (1800 instead of 18:00) and in spoken language in the Army, but not the Navy or Marine Corps, is followed by the word "hours" (e.g., "eighteen hundred hours").

The 24-hour notation is also widely used by astronomers, hospitals, various forms of transportation, and at radio and other broadcast media outlets behind the scenes where scheduling programming needs to be exact, without mistaking AM and PM. In these cases, exact and unambiguous communication of time is critical. If someone mistakes 5:00 AM for 5:00 PM in a hospital for example, when medication or other medical treatment is needed at a certain time, the outcome could be critical. Thus 24-hour time (5:00 PM written as 17:00) is used.


Some style guides and most people suggest not to use a leading zero with a single-digit hour; for example, "3:52 p.m." is preferred over "03:52 p.m.". (The leading zero is more commonly used with the 24-hour notation; especially in computer applications because it can help to maintain column alignment in tables and correct sorting order, and also because it helps to highlight the 24-hour character of the given time.)

Times of day ending in :00 minutes may be pronounced as the numbered hour followed by o'clock (e.g., 10:00 ten o'clock, 2:00 two o'clock, 4:00 four o'clock, etc.). This may be followed by the a.m. or p.m. designator, or might not be, if obvious. O'clock itself may be omitted, leaving a time such as four a.m. or four p.m. Instead of "a.m." and "p.m.", times can also be described as "in the morning", "in the afternoon", "in the evening", or "at night".

The minutes (other than :00) may be pronounced in a variety of ways:

Minutes :01 through :09 are usually pronounced as oh one through oh nine. :10 through :59 are their usual number-words. For example, "9:45 a.m." is usually pronounced "nine forty-five" or sometimes "nine forty-five a.m.".

Times of day from :01 to :29 minutes past the hour are commonly pronounced with the words "after" or "past", for example, 10:17 being "seventeen after ten" or "seventeen past ten". :15 minutes is very commonly called "quarter after" or "quarter past" and :30 minutes universally "half past", e.g., 4:30, "half past four". Times of day from :31 to :59 are, by contrast, given subtractively with the words "to", "of", "until", or "till": 12:55 would be pronounced as "five to one" or "five of one". :45 minutes is pronounced as "quarter to", "quarter of", "quarter until", or "quarter till".

For example, "9:45 a.m." is often pronounced "fifteen till ten" or "quarter to ten", or sometimes "quarter to ten in the morning" (but rarely "quarter to ten a.m.").

However, it is always acceptable to pronounce the time using number words and the aforementioned "oh" convention, for example, 12:55 "twelve fifty-five", 12:09 "twelve oh-nine", 12:30 "twelve thirty", and 12:15 "twelve fifteen". This pronunciation is becoming more common.

See also


  1. ^ Sanderson, Blair (18 January 2016). "Proposed legislation aims to settle date debate". CBC News. Retrieved 25 September 2017.
  2. ^ "9.31: Month and day". The Chicago manual of style (17 ed.). Chicago: The University of Chicago Press. 2017. ISBN 978-0-226-28705-8.
  3. ^ "9.36: ISO style for dates". The Chicago manual of style (17 ed.). Chicago: The University of Chicago Press. 2017. ISBN 978-0-226-28705-8.
  4. ^ a b "9.39: The twenty-four-hour system". The Chicago manual of style (17 ed.). Chicago: The University of Chicago Press. 2017. ISBN 978-0-226-28705-8.
  5. ^ a b c "9.35: All-numeral dates and other brief forms". The Chicago manual of style (17 ed.). Chicago: The University of Chicago Press. 2017. ISBN 978-0-226-28705-8.
  6. ^ "Technical Advisory Group on Machine Readable Travel Documents (TAG/MRTD)" (PDF).
  7. ^ "ICAO Doc 9303 Machine Readable Travel Documents" (PDF).
  8. ^ "6.38: Commas with dates". The Chicago manual of style (17 ed.). Chicago: The University of Chicago Press. 2017. ISBN 978-0-226-28705-8.
  9. ^ [1] Archived 2010-08-01 at the Wayback Machine. National Institute of Standards and Technology.
  10. ^ Staff (March 2010). "SECNAV M-5216.5 Department of the Navy – Correspondence Manual" (PDF). U.S. Secretary of the Navy. p. 2-11 (PDF document page 25/145). Archived from the original (PDF) on 2011-01-03. Retrieved August 10, 2013.
  11. ^ Statutes at Large, 28th Congress, 2nd Session, p. 721.
Calendar date

A calendar date is a reference to a particular day represented within a calendar system. The calendar date allows the specific day to be identified. The number of days between two dates may be calculated. For example, "24 May 2019" is ten days after "14 May 2019" in the Gregorian calendar. The date of a particular event depends on the observed time zone. For example, the air attack on Pearl Harbor that began at 7:48 a.m. Hawaiian time on December 7, 1941, took place at 3:18 a.m. December 8 in Japan (Japan Standard Time).

A particular day may be represented by a different date in another calendar as in the Gregorian calendar and the Julian calendar, which have been used simultaneously in different places. In most calendar systems, the date consists of three parts: the day of month, month, and the year. There may also be additional parts, such as the day of week. Years are usually counted from a particular starting point, usually called the epoch, with era referring to the particular period of time (Note the different use of the terms in geology).

The most widely used epoch is a conventional birthdate of Jesus (which was established by Dionysius Exiguus in the sixth century). A date without the year part may also be referred to as a date or calendar date (such as "24 May" rather than "24 May 2019"). As such, it defines the day of an annual event, such as a birthday or Christmas on 25 December.

Many computer systems internally store points in time in Unix time format or some other system time format.

The date (Unix) command—internally using the C date and time functions—can be used to convert that internal representation of a point in time

to most of the date representations shown here.

The current date in the Gregorian calendar is 24 May 2019. If this is not really the current date, then to update it.

Date and time notation in the United Kingdom

Date and time notation in the United Kingdom records the date using the day-month-year format (21 October 2011 or 21/10/11). The ISO 8601 format (2011-10-21) is increasingly used for all-numeric dates. The time can be written using either the 24-hour clock (16:10) or 12-hour clock (4.10 p.m.).

Time in the United States

Time in the United States, by law, is divided into nine standard time zones covering the states and its possessions, with most of the United States observing daylight saving time (DST) for approximately the spring, summer, and fall months. The time zone boundaries and DST observance are regulated by the Department of Transportation. Official and highly precise timekeeping services (clocks) are provided by two federal agencies: the National Institute of Standards and Technology (NIST) (an agency of the Department of Commerce); and its military counterpart, the United States Naval Observatory (USNO). The clocks run by these services are kept synchronized with each other as well as with those of other international timekeeping organizations.

It is the combination of the time zone and daylight saving rules, along with the timekeeping services, which determines the legal civil time for any U.S. location at any moment.

United States

The United States of America (USA), commonly known as the United States (U.S. or US) or America, is a country comprising 50 states, a federal district, five major self-governing territories, and various possessions. At 3.8 million square miles (9.8 million km2), the United States is the world's third or fourth largest country by total area and is slightly smaller than the entire continent of Europe's 3.9 million square miles (10.1 million km2). With a population of over 327 million people, the U.S. is the third most populous country. The capital is Washington, D.C., and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico. The State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean. The U.S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The extremely diverse geography, climate, and wildlife of the United States make it one of the world's 17 megadiverse countries.Paleo-Indians migrated from Siberia to the North American mainland at least 12,000 years ago. European colonization began in the 16th century. The United States emerged from the thirteen British colonies established along the East Coast. Following the French and Indian War, numerous disputes between Great Britain and the colonies led to the American Revolution, which began in 1775, and the subsequent Declaration of Independence in 1776. The war ended in 1783 with the United States becoming the first country to gain independence from a European power. The current constitution was adopted in 1788, with the first ten amendments, collectively named the Bill of Rights, being ratified in 1791 to guarantee many fundamental civil liberties. The United States embarked on a vigorous expansion across North America throughout the 19th century, acquiring new territories, displacing Native American tribes, and gradually admitting new states until it spanned the continent by 1848.During the second half of the 19th century, the Civil War led to the abolition of slavery. By the end of the century, the United States had extended into the Pacific Ocean, and its economy, driven in large part by the Industrial Revolution, began to soar. The Spanish–American War and World War I confirmed the country's status as a global military power. The United States emerged from World War II as a global superpower, the first country to develop nuclear weapons, the only country to use them in warfare, and a permanent member of the United Nations Security Council. Sweeping civil rights legislation, notably the Civil Rights Act of 1964, the Voting Rights Act of 1965 and the Fair Housing Act of 1968, outlawed discrimination based on race or color. During the Cold War, the United States and the Soviet Union competed in the Space Race, culminating with the 1969 U.S. Moon landing. The end of the Cold War and the collapse of the Soviet Union in 1991 left the United States as the world's sole superpower.The United States is the world's oldest surviving federation. It is a federal republic and a representative democracy. The United States is a founding member of the United Nations, World Bank, International Monetary Fund, Organization of American States (OAS), and other international organizations. The United States is a highly developed country, with the world's largest economy by nominal GDP and second-largest economy by PPP, accounting for approximately a quarter of global GDP. The U.S. economy is largely post-industrial, characterized by the dominance of services and knowledge-based activities, although the manufacturing sector remains the second-largest in the world. The United States is the world's largest importer and the second largest exporter of goods, by value. Although its population is only 4.3% of the world total, the U.S. holds 31% of the total wealth in the world, the largest share of global wealth concentrated in a single country.Despite income and wealth disparities, the United States continues to rank very high in measures of socioeconomic performance, including average wage, human development, per capita GDP, and worker productivity. The United States is the foremost military power in the world, making up a third of global military spending, and is a leading political, cultural, and scientific force internationally.

Date and time notation in the Americas
Sovereign states

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