| Full date | January 24, 2025 24 January 2025 |
|---|---|
| All-numeric date | 01/24/2025 2025-01-24 24 01 25 24 01 2025 |
| Time | 12:27 am 00:27 |
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.[ citation needed ] 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. January 24, 2025) 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 (12:27 am).
International date and time formats typically follow the ISO 8601 format (2025-01-24) for all-numeric dates, [3] write the time using the 24-hour clock (00:27), [4] and notate the date using a day–month–year format (24 January 2025). [5] These forms are increasingly common in American professional, academic, technological, military, and other internationally oriented environments.
In the United States, dates are traditionally written in the "month-day-year" order, with neither increasing nor decreasing order of significance. This is called middle endian. This order is used in both the traditional all-numeric date (e.g., "1/21/24" or "01/21/2024") and the expanded form (e.g., "January 21, 2024"—usually spoken with the year as a cardinal number and the day as an ordinal number, e.g., "January twenty-first, twenty twenty-four"), 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, other than the year-month-day format advocated by ISO 8601, as it is not comprehensible to readers outside the United States. [5] [6]
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 1942" (sometimes with hyphens). [5] Many genealogical databases and the Modern Language Association citation style use this format. Visas and passports issued by the U.S. State Department also use the day-month-year order for human-readable dates and year-month-day for all-numeric encoding, in compliance with the International Civil Aviation Organization's standards for machine-readable travel documents. [7] [8]
The fully written "day-month-year" (e.g., 25 August 2006) in written American English is recommended by the Chicago Manual of Style for material that requires many full dates, as it does not require commas. [9]
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 alphanumerically will automatically result in the content being listed chronologically.
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 [10] [11] ), the earliest of which is traceable back to 1968. This is only required when compliance with the given standard is, or was, required.
The United States military uses four formats for standard military correspondence:
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").[ citation needed ]
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". [14] Calendars mostly show Sunday as the first day of the week.
The United States 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. It is also not uncommon for AM and PM to be shortened to A and P.
The 24-hour clock is used in military, public safety, and scientific contexts in the United States. [4] It is best known for its use by the military and is therefore commonly called "military time". In U.S. military use, 24-hour time is traditionally written without a colon (1800 instead of 18:00). For exact hour times, they are referred to as "hundred", so 10:00 would be referred to as "ten hundred hours" and 11:00 as "eleven hundred hours", from the mathematical interpretation of the numeral sequence. Hours between 1 and 10 have their leading zero spoken as "oh", as in "oh eight thirty" to mean 8:30 a.m., although 00:30 would be "zero thirty". The Army adds the word "hours" after the military time (e.g. "eighteen hundred hours"), including for times not on the hour mark (e.g. "sixteen thirty hours"); however, the Navy and Marine Corps do not do this. Midnight is known interchangeably as either "zero hundred" or "twenty four hundred", often chosen based on whether it is the start or end of a time range, respectively, though there are no times "higher" than 2400. [15]
The 24-hour notation is also widely used by astronomers, hospitals, public safety personnel (police, fire department, EMS), 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 dire. Thus 24-hour time (5:00 PM written as 17:00) is used.
Some style guides and most persons 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 as ten o'clock, 2:00 as two o'clock, 4:00 as 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" the current hour, 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".
:45 minutes is pronounced as "quarter to", "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".
However, it is always acceptable to pronounce the time using number words and the aforementioned "oh" convention, for example, 12:55 as "twelve fifty-five", 12:09 as "twelve oh-nine", 12:30 as "twelve thirty", and 12:15 as "twelve fifteen".
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, "25 January 2025" is ten days after "15 January 2025". 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 7 December 1941 took place at 3:18 a.m. Japan Standard Time, 8 December in Japan.
ISO 8601 is an international standard covering the worldwide exchange and communication of date and time-related data. It is maintained by the International Organization for Standardization (ISO) and was first published in 1988, with updates in 1991, 2000, 2004, and 2019, and an amendment in 2022. The standard provides a well-defined, unambiguous method of representing calendar dates and times in worldwide communications, especially to avoid misinterpreting numeric dates and times when such data is transferred between countries with different conventions for writing numeric dates and times.
The modern 24-hour clock is the convention of timekeeping in which the day runs from midnight to midnight and is divided into 24 hours. This is indicated by the hours passed since midnight, from 00(:00) to 23(:59), with 24(:00) as an option to indicate the end of the day. This system, as opposed to the 12-hour clock, is the most commonly used time notation in the world today, and is used by the international standard ISO 8601.
Midnight is the transition time from one day to the next – the moment when the date changes, on the local official clock time for any particular jurisdiction. By clock time, midnight is the opposite of noon, differing from it by 12 hours.
A timestamp is a sequence of characters or encoded information identifying when a certain event occurred, usually giving date and time of day, sometimes accurate to a small fraction of a second. Timestamps do not have to be based on some absolute notion of time, however. They can have any epoch, can be relative to any arbitrary time, such as the power-on time of a system, or to some arbitrary time in the past.
A year zero does not exist in the Anno Domini (AD) calendar year system commonly used to number years in the Gregorian calendar ; in this system, the year 1 BC is followed directly by year AD 1. However, there is a year zero in both the astronomical year numbering system, and the ISO 8601:2004 system, a data interchange standard for certain time and calendar information. There is also a year zero in most Buddhist and Hindu calendars.
Different conventions exist around the world for date and time representation, both written and spoken.
Date and time notation in Canada combines conventions from the United Kingdom, conventions from the United States, and conventions from France, often creating confusion. The Government of Canada specifies the ISO 8601 format for all-numeric dates. It recommends writing the time using the 24-hour clock (16:22) for maximum clarity in both Canadian English and Canadian French, but also allows the 12-hour clock (4:22 p.m.) in English.
In Finland, the usual way of writing dates in normal text is with the months spelled out. The format varies according to the language used. In Finnish, a full stop is placed after the day to indicate an ordinal: 31. toukokuuta 2002; furthermore, the month is in the partitive case, always marked by -ta. The month can also be written first, now in genitive case : toukokuun 31. pnä 2002. In Swedish, the full stop is not used and the month is in nominative : den 31 maj 2002.
In Poland, the official system for representing dates and times follows the international ISO 8601 standard. However, in less official use, other conventions prevail, such as the day-month-year order and several Polish language abbreviations.
Date and time notation in Sweden mostly follows the ISO 8601 standard: dates are generally written in the form YYYY-MM-DD. Although this format may be abbreviated in a number of ways, almost all Swedish date notations state the month between the year and the day. Months are not capitalised when written. The week number may also be used in writing and in speech. Times are generally written using 24-hour clock notation, with full stops as separators, although 12-hour clock notation is more frequently used in speech.
Date and time notation in the United Kingdom records the date using the day–month–year format. The time can be written using either the 24-hour clock (23:59) or the 12-hour clock (11:59 p.m.), either with a colon or a full stop (11.59 p.m.).
The European Committee for Standardization (CEN) and (CENELEC) adopted ISO 8601 with EN 28601, now EN ISO 8601. As a European Norm, CEN and CENELEC member states are obligated to adopt the standard as national standard without alterations as well.
Thailand has adopted ISO 8601 under national standard: TIS 1111:2535 in 1992. However, Thai date and time notation reflects the country’s cultural development through the years used. The formal date format is D/M/YYYY format (1/6/2568), nowadays using the Buddhist Era (BE). The full date format is day-month-year format which is written in Thai. While a 24-hour system is common for official use, colloquially, a 12-hour format with terms like "morning" and "night", etc., or a modified six-hour format is used.
Date and time notation in the Philippines varies across the country in various, customary formats. Some government agencies in the Philippines have adopted time and date representation standard based on the ISO 8601, notably the Philippines driver's license and the Unified Multi-Purpose ID.
The most formal manner of expressing the full date and/or time in South Korea is to suffix each of the year, month, day, ante/post-meridiem indicator, hour, minute and second with the corresponding unit and separating each with a space:
The date and time in Australia are most commonly recorded using the day–month–year format and the 12-hour clock, although 24-hour time is used in some cases. For example, some public transport operators such as V/Line and Transport NSW use 24-hour time, although others use 12-hour time instead.
Date and time notation in Italy records the date using the day–month–year format. The time is written using the 24-hour clock (22:42); in spoken language and informal contexts, the 12-hour clock is more commonly adopted, but without using "a.m." or "p.m." suffixes (10:42).
A GeneralizedTime is a time format in the ASN.1 notation. It consists of a string value representing the calendar date, as defined in ISO 8601, a time of day with an optional fractional seconds element and the optional local time differential factor as defined in ISO 8601.
Date and time notation in New Zealand most commonly records the date using the day-month-year format, while the ISO 8601 format (2025-01-23) is increasingly used for all-numeric dates, such as date of birth. The time can be written using either the 12-hour clock or the 24-hour clock (11:42).
