NonUTC

Non-UTC refers to time representations that are not expressed in Coordinated Universal Time (UTC). In everyday use, non-UTC typically means local civil time or timestamps that include a time zone or offset from UTC, rather than a pure UTC timestamp.

Non-UTC time encompasses several related concepts. Civil time is the local time observed in a region, which often includes daylight saving time adjustments. Time zones are regions with defined offsets from UTC, typically varying with geographic location and sometimes changing by law. Some historical or regional times use local solar or mean solar time, which can differ from modern standardized offsets. In addition, some standards allow timestamps with a fixed offset from UTC, such as 2024-07-01T12:00:00+02:00, which explicitly denotes a non-UTC time.

Conversion and ambiguity are central issues. To interpret non-UTC times unambiguously, you must know the exact offset and any daylight saving rules in effect at the given moment. Offsets can change, and many regions have non-uniform rules or have abolished DST, making historical times harder to interpret. Abbreviations for time zones (for example, EST or CET) can be ambiguous without context, because different regions may share the same abbreviation.

Standards and data sources support non-UTC information. ISO 8601 allows offsets from UTC, and the IANA time zone database provides rules for converting local times to and from UTC for a given region. In computing practice, it is common to store times in UTC and convert to local time for display, to avoid ambiguity and ensure consistent cross-system interoperability. Leap seconds, while part of UTC, are generally not represented in straightforward local-time values.