ISO 8601 - Times

Times

ISO 8601 uses the 24-hour clock system. The basic format is and the extended format is ::.

• refers to a zero-padded hour between 00 and 24 (where 24 is only used to notate midnight at the end of a calendar day).
• refers to a zero-padded minute between 00 and 59.
• refers to a zero-padded second between 00 and 60 (where 60 is only used to notate an added leap second).

So a time might appear as either "134730" in the basic format or "13:47:30" in the extended format.

It is also acceptable to omit lower order time elements for reduced accuracy: :, and are all used. (The use of alone is considered basic format.)

Midnight is a special case and can be referred to as both "00:00" and "24:00". The notation "00:00" is used at the beginning of a calendar day and is the more frequently used. At the end of a day use "24:00". Note that "2007-04-05T24:00" is the same instant as "2007-04-06T00:00" (see Combined date and time representations below).

Decimal fractions may also be added to any of the three time elements. A decimal mark, either a comma or a dot (without any preference as stated in resolution 10 of the 22nd General Conference CGPM in 2003, but with a preference for a comma according to ISO 8601:2004) is used as a separator between the time element and its fraction. A fraction may only be added to the lowest order time element in the representation. To denote "14 hours, 30 and one half minutes", do not include a seconds figure. Represent it as "14:30,5", "1430,5", "14:30.5", or "1430.5". There is no limit on the number of decimal places for the decimal fraction. However, the number of decimal places needs to be agreed to by the communicating parties.