How Time Zones Work
UTC as the reference
Coordinated Universal Time, or UTC, is the reference used by time zones around the world. Each zone is described by its offset from UTC, such as UTC+9 for Japan or UTC-5 for New York in standard time.
The offset is stable for some zones and changes twice a year for zones that observe daylight saving time.
IANA time zone identifiers
IANA identifiers such as America/New_York, Europe/London, and Asia/Tokyo name a zone by region and location. They are the standard used by operating systems, programming languages, and calendars.
The IANA time zone database also maps each zone to the countries and territories that use it.
Daylight saving time
Many zones switch between a standard offset and a daylight-saving offset during the year. The time zone pages here show both values from the IANA dataset.
For an exact local time, check a clock or calendar in the destination rather than relying on a static offset.