Datetime

Datetime is a representation of date and time as a data type or unit of information used in computing and record-keeping. It combines components such as calendar date (year, month, day) with clock time (hour, minute, second, and optional fractions) and may include time zone or offset from UTC. Datetime values enable scheduling, time-stamping, interval calculations, and chronological ordering across systems and locales.

Most systems support a standard textual representation based on ISO 8601, for example 2025-12-06T14:30:00Z for a moment in UTC, or 2025-12-06T14:30:00+02:00 for a local offset. Textual formats vary by locale, but parsing and formatting functionality is common in programming languages.

Epoch time, or Unix time, counts seconds since 1970-01-01 UTC and is a widely used portable representation for instants. Durations or intervals measure elapsed time between instants and can be added to dates to compute future moments.

Time zones and daylight saving time introduce complexity: the same instant may be represented in different local times, and some local times are ambiguous or nonexistent during transitions. The IANA time zone database provides rules for converting between global instants and local wall times.

In programming, datetime is often a built-in type or library module. Typical capabilities include constructing values from components, parsing strings, formatting output, performing arithmetic, comparing instants, and converting between time zones and UTC. Examples include Python's datetime, Java's java.time, and C#'s DateTime and DateTimeOffset.

Common challenges include leap years, leap seconds occasionally added to UTC, and historical calendar changes. Consistent use of a single reference such as UTC helps avoid confusion across systems.