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 (31 December 1999, 31/12/99 or 31/12/1999). The ISO 8601 format (1999-12-31) is increasingly used for all-numeric dates. The time can be written using either the 24-hour clock (23:59) or the 12-hour clock (11:59 pm).

Date

Date notation in English

Dates are traditionally and most commonly written in day–month–year (DMY) order:

* 31 December 1999
* 31/12/99

Formal style manuals discourage writing the day of the month as an ordinal number (for example "31st December"), except with an incomplete reference, such as "They set off on 12 August 1960 and arrived on the 18th".

When saying the date, it is usually pronounced using "the", then the ordinal number of the day first, then the preposition "of", then the month (for example "the thirty-first of December"). The month-first form (for example "December the third") was widespread until the mid-20th century and remains the most common format for newspapers across the United Kingdom. Example: ''The Times'' and the British tabloids ('' Daily Mail, Daily Mirror, The Sun, Daily Express'') all have 'Friday, December 31 2021', while ''The Guardian'', the ''Financial Times'' and ''The Daily Telegraph'' all have 'Friday 31 December 2021'. Consequently in the UK there is no standard pattern for long form dates when printed, as opposed to when using numeric dates, for which there are standard formats.

The month-first format is still spoken, perhaps more commonly when not including a year in the sentence. When the date is written out in full, or when spoken, usage can be one or the other. Neither is distinctly preferred over the other, and there is no risk of ambiguity.

All-numeric dates

All-numeric dates are used in notes and references, but not running prose. They can be written in several forms. For example, to represent 31 December 1999:

* 31/12/99 ''or'' 31.12.99
* 31.xii.99 (unusual)
* 1999-12-31 (unusual except when required for sorting purposes)

The year may also be written in full (31/12/1999). It contrasts with date and time notation in the United States, where the month is placed first, leading to confusion in international communications: in the United States, 2/11/03 is interpreted as 11 February 2003. To remedy this, the month is sometimes written in Roman numerals, a format common in some European countries: 2.xi.03.

The ISO 8601 format (adopted as British Standard BS ISO 8601:2004) is unambiguous and machine-readable, and increasingly popular in technical, scientific, financial, and computing contexts. It also has the desirable property that lists of dates in this format, when sorted lexicographically correspond to their chronological order. The Government Digital Service requires it for all forms of data transmission. Dates in this format are separated with hyphens: 2003-11-02.

Weeks

Weeks are generally referred to by the date on which they start, with Monday often treated as the first day of the week, for example "the week commencing 5 March". Some more traditional calendars instead treat Sunday as the first day of the week. ISO 8601 week numbers are found in diaries and are used in business.

Date notation in Welsh

The day–month–year order is also used in modern Welsh:

*
* ''or'' (The suffix indicates an ordinal number, like "th" in English.)

The month–day–year order (for example "") was previously more common: it is usual to see a Welsh month–day–year date next to an English day–month–year date on a bilingual plaque from the latter half of the 20th century.

"" is read as with the usual soft mutation of ''M'' to ''F'' after ''o'' ("of"). The year 1999 can be read as either (thousand nine nine nine) or (one nine nine nine).

Time

Time notation in English

Both the 24-hour and 12-hour notations are used in the United Kingdom, for example:

* 23:59 ''or'' 23.59
* 11.59 p.m.

The 24-hour notation is used in timetables and on most digital clocks, but 12-hour notation is still widely used in ordinary life. The 24-hour notation is used more often than in North America – transport timetables use it exclusively, as do most legal documents – but not as commonly as in much of the non-English-speaking world. The BBC
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