Question 1

What is UTC and how does it differ from GMT?

Accepted Answer

UTC (Coordinated Universal Time) is the primary international time standard maintained by atomic clocks at the International Bureau of Weights and Measures. GMT (Greenwich Mean Time) is a time zone — the time zone of the United Kingdom in winter — based on the mean solar time at the Prime Meridian in Greenwich, England. In everyday use the two are interchangeable, but technically UTC is defined by atomic clocks while GMT is defined by Earth's rotation. UTC is the correct term in scientific, computing, and aviation contexts.

Question 2

How accurate is the time shown on this site?

Accepted Answer

The time displayed on this site is as accurate as your device's own clock. All time calculations are performed in your browser using the IANA timezone database — the same database used by your operating system, smartphone, and every major programming language. We do not make any server requests to calculate the time. If your device clock is synchronised with an NTP (Network Time Protocol) server — which all modern smartphones and computers do automatically — the time shown here will be accurate to within a fraction of a second.

Question 3

What is Daylight Saving Time (DST) and when does it change?

Accepted Answer

Daylight Saving Time (DST) is the practice of advancing clocks by one hour during the warmer months to extend usable daylight into the evening. In the United States and Canada, DST begins on the second Sunday of March (clocks spring forward) and ends on the first Sunday of November (clocks fall back). In the European Union, DST begins on the last Sunday of March and ends on the last Sunday of October. Many countries — including Japan, China, India, and most of Africa — do not observe DST at all.

Question 4

What is the difference between a time zone and a UTC offset?

Accepted Answer

A UTC offset is a simple number — the number of hours (and sometimes minutes) that a location is ahead of or behind UTC. For example, UTC+5:30 means the local time is 5 hours and 30 minutes ahead of UTC. A time zone is a broader concept that includes the UTC offset, any DST rules, and the history of all previous offsets for a given region. New York is in the Eastern Time zone, which has a UTC offset of UTC-5 in winter (Eastern Standard Time) and UTC-4 in summer (Eastern Daylight Time).

Question 5

Which countries do not observe Daylight Saving Time?

Accepted Answer

The majority of the world's countries do not observe Daylight Saving Time. Notable examples include Japan, China, India, Singapore, South Korea, most of Africa, most of the Middle East (except Iran and some others), Brazil (abolished DST in 2019), Russia (permanently on summer time since 2014), and Argentina. In the United States, Arizona (except the Navajo Nation) and Hawaii do not observe DST. The equatorial regions generally do not observe DST because sunrise and sunset times are relatively consistent year-round.

Question 6

How do I convert a time from one time zone to another?

Accepted Answer

The simplest method is to convert both times to UTC first, then compare. Find the UTC offset of the source timezone, subtract it from the local time to get UTC, then add the UTC offset of the destination timezone. For example, to convert 3:00 PM New York (UTC-5) to Tokyo (UTC+9): add 5 hours to get 8:00 PM UTC, then add 9 hours to get 5:00 AM the next day in Tokyo. You can also use the Timezone Converter on this site, which handles DST automatically.

Question 7

Why does India use UTC+5:30 instead of a whole-hour offset?

Accepted Answer

India uses UTC+5:30 (Indian Standard Time) as a single time zone across the entire country, despite spanning nearly 30 degrees of longitude. The half-hour offset was chosen in 1906 as a geographic compromise between the solar times of Calcutta (approximately UTC+5:53) and Bombay (approximately UTC+4:51). India has never observed Daylight Saving Time, and proposals to split the country into two time zones have been rejected on grounds of national unity and administrative simplicity.

Question 8

What is the IANA timezone database?

Accepted Answer

The IANA Timezone Database (also called the tz database or Olson database) is a comprehensive, freely available record of historical and current time zone rules for every location on Earth. It is maintained by the Internet Assigned Numbers Authority and updated whenever governments announce changes to their time zone rules. Every major operating system, programming language, and web browser uses it. Time zones in the database are identified by names like 'America/New_York', 'Europe/London', and 'Asia/Tokyo'. This site uses the IANA database embedded in your browser to display accurate times.

Question 9

Why is China in a single time zone when it spans five natural time zones?

Accepted Answer

China uses a single national time zone — China Standard Time (CST) at UTC+8 — across the entire country, despite spanning approximately 60 degrees of longitude from east to west. This was introduced in 1949 after the founding of the People's Republic of China as a symbol of national unity. In practice, the westernmost province of Xinjiang is geographically about 3 hours behind Beijing, meaning the sun does not rise until after 10am in winter by official time. Many residents of Xinjiang informally use 'Xinjiang time' (UTC+6) in their daily lives.

Question 10

What is the International Date Line and where is it?

Accepted Answer

The International Date Line is an imaginary line running roughly along the 180th meridian in the Pacific Ocean, where the calendar date changes by one day. Cross it heading west and you advance one day; cross it heading east and you go back one day. The line is not straight — it bends around the Aleutian Islands, Fiji, Tonga, and Kiribati to avoid splitting countries and island groups between two calendar dates. In 1995, Kiribati moved the date line significantly eastward so that all of its territory would be in the same calendar day.

Question 11

How does Daylight Saving Time affect international meeting scheduling?

Accepted Answer

DST transitions can change the time difference between two locations by one or even two hours. For example, when the United States transitions to DST in March but Europe has not yet transitioned (Europe transitions about two weeks later), the offset between New York and London temporarily changes from 5 hours to 4 hours. Teams scheduling recurring international meetings need to be aware of these transition windows, which typically occur in March–April and October–November. Using a world clock tool that accounts for DST — like this site — is the most reliable way to verify the current offset between any two locations.

Question 12

What is Nepal's unusual UTC+5:45 time zone?

Accepted Answer

Nepal Standard Time (NPT) at UTC+5:45 is one of the most unusual time zones in the world — a quarter-hour offset with no geographic justification. Nepal's geographic centre corresponds to approximately UTC+5:41, which would round naturally to UTC+5:30 (the same as India). The choice of UTC+5:45 was deliberate: it places Nepal 15 minutes ahead of India, asserting a distinct national identity and independence from its much larger neighbour. The offset has been in use since 1956.

Question 13

Why do some time zones use half-hour offsets?

Accepted Answer

Half-hour UTC offsets typically reflect historical compromises between geographic solar time and the desire to align with neighbouring countries or maintain a single national time zone. India (UTC+5:30) chose its offset as a midpoint between its eastern and western extremes. Australia's Northern Territory and South Australia use UTC+9:30 as a compromise between the eastern states (UTC+10) and Western Australia (UTC+8). Iran uses UTC+3:30 to sit between Iraq (UTC+3) and Afghanistan (UTC+4:30). These decisions were made decades or centuries ago and are rarely changed.

Question 14

What happened when Russia abolished Daylight Saving Time?

Accepted Answer

Russia abolished Daylight Saving Time in 2014 under President Vladimir Putin, following years of public complaints about the health effects of the biannual clock change. Russia initially moved to permanent summer time, but the dark winter mornings proved unpopular, and later that year Russia switched to permanent standard time, where it has remained since. Moscow is now permanently at UTC+3. The abolition was widely welcomed by the Russian public, and Russia's experience has been cited by other countries considering similar moves.

Question 15

How do I find the time in any city?

Accepted Answer

Use the search bar at the top of the home page — type the name of any city and you will be taken directly to that city's clock page, showing the exact current time, UTC offset, timezone identifier, sunrise and sunset times, and a list of other cities in the same timezone. The site covers over 170 cities across all continents. If you cannot find a specific city, look for the nearest major city in the same timezone — for example, if you need the time in Sacramento, California, use Los Angeles, which is in the same Pacific Time zone.

Question 16

What is the difference between Eastern Standard Time and Eastern Daylight Time?

Accepted Answer

Eastern Standard Time (EST) is UTC-5, observed in the eastern United States and Canada during winter (from the first Sunday in November to the second Sunday in March). Eastern Daylight Time (EDT) is UTC-4, observed during summer (from the second Sunday in March to the first Sunday in November). The term 'Eastern Time' (ET) refers to the zone in general, without specifying whether DST is currently in effect. When scheduling meetings, it is important to specify whether you mean EST or EDT, as the UTC offset differs by one hour.

Question 17

Does the time shown change automatically for Daylight Saving Time?

Accepted Answer

Yes. Because all time calculations are performed in your browser using the IANA timezone database, the times displayed on this site automatically reflect the correct UTC offset for each location at any given moment — including DST transitions. When a city switches to or from DST, the time shown for that city will update automatically without any action required on your part. Your own local time is also detected automatically from your device's timezone settings.

Question 18

What is Unix time and how does it relate to UTC?

Accepted Answer

Unix time (also called Unix timestamp or POSIX time) is the number of seconds that have elapsed since January 1, 1970, 00:00:00 UTC — a reference point known as the Unix epoch. It is the most widely used time representation in computing: databases, APIs, server logs, and programming languages all use Unix timestamps internally. Because Unix time is defined relative to UTC, it is unambiguous and timezone-independent. Converting a Unix timestamp to a local time requires knowing the UTC offset of the target timezone, which is where the IANA database comes in.

Question 19

Why do some countries observe DST at different times than others?

Accepted Answer

DST transition dates are set independently by each country's government, and there is no international coordination requirement. The United States transitions on the second Sunday of March and first Sunday of November. The European Union transitions on the last Sunday of March and last Sunday of October. Australia's southern states transition in October and April (reversed because the seasons are reversed in the Southern Hemisphere). This lack of coordination means that for several weeks each year, the time difference between two DST-observing countries in different hemispheres or with different transition rules will be different from its usual value.

Question 20

How can I embed a world clock on my own website?

Accepted Answer

The simplest way to embed a world clock is to use an iframe pointing to a clock page on this site, or to use the JavaScript Intl.DateTimeFormat API directly in your own code. The Intl API is built into all modern browsers and uses the IANA timezone database, so no external library is required. For example, to display the current time in Tokyo: new Intl.DateTimeFormat('en-US', { timeZone: 'Asia/Tokyo', hour: '2-digit', minute: '2-digit', second: '2-digit' }).format(new Date()). Update this with setInterval every second for a live clock.

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