Understanding UTC offsets and IANA time zones

When working with time zones you'll see two very different kinds of identifiers: UTC offsets (like UTC+2) and IANA time zone names (like Europe/Berlin). Understanding the difference is key to getting times right.

What is a UTC offset?

A UTC offset is simply the difference, in hours and minutes, between a location's local time and Coordinated Universal Time (UTC). For example, UTC+2 means local time is two hours ahead of UTC. The crucial catch: a location's offset can change during the year because of daylight saving time.

What is an IANA time zone?

An IANA time zone (such as Europe/Berlin, America/New_York, or Asia/Tokyo) is a named region whose clocks have always followed the same rules. The IANA database encodes the full history and future rules of when each region changes its offset — including daylight saving transitions and historical changes.

Why you should store the IANA name, not the offset

• An offset is only valid for a specific instant; it can change twice a year.
• An IANA name lets software compute the correct offset for any date, past or future.
• Governments occasionally change DST rules — IANA names get updated, fixed offsets don't.

A concrete example

Berlin is UTC+1 in winter (Central European Time) and UTC+2 in summer (Central European Summer Time). If you stored "UTC+1" for a Berlin meeting in July, you'd be an hour off. If you store "Europe/Berlin", the correct offset is always derived automatically.

Every clock and converter on this site is built on IANA time zones via the tz database, so offsets and daylight saving changes are always accurate for the date in question.