What is UTC (Coordinated Universal Time)?

UTC is the primary time standard by which the world regulates clocks and time. It is a successor to Greenwich Mean Time (GMT) and is based on atomic clocks, making it extremely precise. UTC does not observe Daylight Saving Time and serves as the global reference for all time zones.

What is GMT (Greenwich Mean Time)?

GMT was originally the mean solar time at the Royal Observatory in Greenwich, London. While often used interchangeably with UTC, GMT is technically a time zone (UTC+0). GMT may observe Daylight Saving Time in the UK (as BST - British Summer Time).

What is the difference between UTC and GMT?

UTC is a precise atomic time standard, while GMT is a time zone. For most practical purposes, UTC and GMT (when not observing DST) are the same. However, UTC is the international scientific standard and does not change for DST.

How do timezones work?

Timezones are geographical regions observing a uniform standard time. The Earth is divided into 24 main timezones based on longitude, offset from UTC. Political boundaries and regional decisions often influence their exact shape and rules.

What are common time zone abbreviations like EST, PST, CST, IST?

EST (Eastern Standard Time), PST (Pacific Standard Time), CST (Central Standard Time), and IST (Indian Standard Time) are common names for local time in specific regions. These abbreviations can sometimes be ambiguous (e.g., CST can refer to Central, China, or Cuba Standard Time). Using IANA timezone names (e.g., 'America/New_York') is more precise and recommended for clarity, especially in international contexts.

What is Daylight Saving Time (DST)?

DST is the practice of advancing clocks (typically by one hour) during warmer months to make better use of natural daylight in the evenings. Not all regions observe DST, and the start/end dates and rules vary significantly by location.

What is the International Date Line (IDL)?

The IDL is an imaginary line on the surface of the Earth that runs from the north pole to the south pole and demarcates the change of one calendar day to the next. It roughly follows the 180° line of longitude but deviates to pass around some territories and island groups. Crossing the IDL eastward subtracts a day; crossing westward adds a day.

What is the IANA Time Zone Database (tzdata)?

The IANA Time Zone Database, also known as tzdata or the Olson database, is a collaborative compilation of information about world time zones. It aims to be a comprehensive record of historical and current time zone rules, including DST transitions. Most operating systems and software use tzdata for time zone calculations.

How do I use the World Time Converter on this site?

To use our World Time Converter: 1. Select the date. 2. Input the time. 3. Choose your 'From Timezone'. 4. Choose your 'To Timezone'. The converted times will display automatically. Access it here: World Time Converter .

Understanding Timezones, DST, UTC, GMT & IANA | World Time Glance

Understanding Key Time Concepts

Core definitions and how they relate to each other.

UTC, or Coordinated Universal Time, is the primary time standard by which the world regulates clocks and time. It's a highly precise atomic time standard, maintained by a network of atomic clocks. UTC itself does not observe Daylight Saving Time (DST). It serves as a global reference point; all other time zones are expressed as an offset from UTC (e.g., UTC-5, UTC+10).

Global Time Systems & Standards

Learn about systems governing global time.

Practical Time Management

Tips for using timezones effectively.

Explore Our Time Tools

Ready to put your knowledge to use? Our tools help navigate global time. Use our timezone converter or browse our world clock.

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What is UTC (Coordinated Universal Time)?

What is GMT (Greenwich Mean Time)?

UTC vs. GMT: What's the Difference?

How Timezones Work

Time Zone Abbreviations (EST, PST, etc.)

A Brief History of Timezones

Understanding Daylight Saving Time (DST)

The International Date Line (IDL)

IANA Time Zone Database (tzdata)

Tips for Dealing with Timezones

Common Timezone Challenges

Using Our World Time Converter

Explore Our Time Tools