A Guide to Global Time Zones

Time zones synchronize regions of the earth by determining their offset from a single, globally coordinated baseline. Originally established to align complex railroad schedules across vast distances, they are now the foundation of our entire digitally synchronized world.

The Anchor: UTC

UTC stands for Coordinated Universal Time. It is the primary time standard by which the world regulates clocks and time.

Crucially, UTC never changes for Daylight Saving Time (DST). It remains fixed all year round, acting as the infallible anchor point from which every other time zone is calibrated.

Offsets

A time zone tells you how far "ahead" or "behind" a region is compared to UTC. This difference is called the offset.

Offsets are defined in hours and minutes: ±hh:mm.

Example 1: Behind UTC

If UTC is 12:00 PM, and New York is at a -05:00 offset, the time in New York is 7:00 AM.

Example 2: Ahead of UTC

If UTC is 12:00 PM, and Tokyo is at a +09:00 offset, the time in Tokyo is 9:00 PM.

Not just whole hours: While most zones are offset by whole hours, some are offset by half or quarter hours! For example, India is at +05:30, and Kathmandu is at +05:45.

The Problem with Abbreviations

Time zone abbreviations like EST (Eastern Standard Time) or PST (Pacific Standard Time) are incredibly common in daily conversation, but they are notoriously problematic for scheduling.

Many abbreviations are highly ambiguous. For instance, what does IST stand for?

India Standard Time (+05:30)
Israel Standard Time (+02:00)
Irish Standard Time (+01:00)

The City-Based Standard (IANA)

To solve this ambiguity, modern software uses the rigorous IANA Time Zone Database. This system uses a "Continent/City" naming convention. Instead of guessing what "EST" means, modern apps specify America/New_York.

Using a major city uniquely identifies the geographic region, unequivocally determining both its base offset from UTC and the specific rules regarding when (and if) that region observes Daylight Saving Time.

Daylight Saving Time (DST)

Adding entirely another layer of complexity is Daylight Saving Time - the practice of advancing clocks forward (typically by one hour) during warmer months so that darkness falls at a later clock time.

Different Dates: The exact dates and times when clocks "spring forward" or "fall back" differ wildly between countries, and sometimes even between regions within a single country.
Shifting Offsets: When DST is observed, the actual offset from UTC changes. For example, America/New_York operates at -05:00 in the winter (EST), but shifts to -04:00 in the summer (EDT).

This constant, staggered shifting is specifically why coordinating global meetings is such a notorious headache, and exactly why we built timee.io - to make that complex math visual and effortless.