WWorldTimeAll time guides →

Standards

IANA time zones vs UTC offsets: what is the difference?

UTC+1 is a number. Europe/Paris is a history, a rule set and a prediction for a particular place.

An offset answers one narrow question

A UTC offset tells you the difference between UTC and a local clock at a particular instant. It is excellent for displaying a finished conversion, but it carries no information about where the rule came from or when it may change.

An IANA identifier carries rules

An IANA identifier such as Europe/Paris or America/New_York identifies a representative location and its known civil-time transitions. It lets a program calculate the correct offset for a past or future date, including daylight saving time.

Store the place with the event

For a future meeting, record the local wall time, date and time-zone identifier. Do not store only the current offset. If the jurisdiction changes its clocks before the meeting, updated time-zone data can apply the revised rule.

Keep exploring