UTC Timezones Explained

Complete guide to all 36 UTC timezone offsets worldwide

$ cat ./docs/utc-intro.md

What is UTC?

UTC (Coordinated Universal Time) is the primary time standard used to regulate clocks and time worldwide. It replaced Greenwich Mean Time (GMT) as the international civil time standard and serves as the reference point for all timezone calculations.

Unlike local times, UTC does not change with daylight saving time. All timezones are defined as offsets from UTC, ranging from UTC-12 (Baker Island) to UTC+14 (Line Islands, Kiribati).

The world uses 37 distinct UTC offsets, including standard hourly offsets and several half-hour (±:30) and quarter-hour (±:45) variations used by countries like India (UTC+5:30), Nepal (UTC+5:45), and the Chatham Islands (UTC+12:45).

$ tz --list --all | 36 zones

UTC OFFSET	ABBR	MAJOR CITIES
UTC12	BIT	Baker Island , Howland Island
UTC11	SST	Midway , Pago Pago, Alofi
UTC10	HST	Honolulu , Hilo, Pearl City, Maui
UTC9	AKST	Anchorage , Juneau, Fairbanks, Sitka
UTC8	PST	Los Angeles , San Francisco, Seattle, Las Vegas, San Diego, Portland, Vancouver
UTC7	MST	Denver , Phoenix, Salt Lake City, Albuquerque, Calgary, Edmonton
UTC6	CST	Chicago , Houston, Dallas, Austin, Mexico City, San Antonio, Minneapolis
UTC5	EST	New York , Miami, Toronto, Boston, Philadelphia, Atlanta, Detroit, Montreal
UTC4	VET	Caracas , Santiago, Santo Domingo, La Paz, San Juan, Halifax
UTC3:30	NST	St. John's , Newfoundland, Labrador
UTC3	BRT	São Paulo , Rio de Janeiro, Buenos Aires, Brasília, Salvador, Montevideo
UTC2	GST	South Georgia , Fernando de Noronha
UTC1	AZOT	Azores , Cape Verde, Praia, Ponta Delgada
UTC+0	GMT	London , Dublin, Lisbon, Edinburgh, Casablanca, Reykjavik, Accra
UTC+1	CET	Paris , Berlin, Madrid, Rome, Amsterdam, Brussels, Vienna, Prague, Warsaw, Barcelona
UTC+2	EET	Helsinki , Athens, Cairo, Johannesburg, Kiev, Bucharest, Istanbul, Jerusalem, Cape Town
UTC+3	MSK	Moscow , St. Petersburg, Riyadh, Baghdad, Nairobi, Minsk, Kuwait City, Doha
UTC+3:30	IRST	Tehran , Mashhad, Isfahan, Karaj, Tabriz
UTC+4	GST	Dubai , Abu Dhabi, Baku, Tbilisi, Yerevan, Muscat, Port Louis
UTC+4:30	AFT	Kabul , Kandahar, Herat, Mazar-i-Sharif
UTC+5	PKT	Karachi , Lahore, Tashkent, Islamabad, Ashgabat, Dushanbe
UTC+5:30	IST	New Delhi , Mumbai, Kolkata, Bangalore, Chennai, Hyderabad, Pune, Colombo
UTC+5:45	NPT	Kathmandu , Pokhara, Lalitpur, Biratnagar
UTC+6	BST	Dhaka , Almaty, Bishkek, Thimphu, Chittagong
UTC+6:30	MMT	Yangon , Mandalay, Naypyidaw, Cocos Islands
UTC+7	ICT	Bangkok , Jakarta, Ho Chi Minh City, Hanoi, Phnom Penh, Vientiane
UTC+8	CST	Shanghai , Beijing, Hong Kong, Singapore, Taipei, Kuala Lumpur, Perth, Shenzhen
UTC+9	JST	Tokyo , Seoul, Osaka, Pyongyang, Sapporo, Kyoto, Busan
UTC+9:30	ACST	Adelaide , Darwin, Alice Springs
UTC+10	AEST	Sydney , Melbourne, Brisbane, Canberra, Port Moresby, Vladivostok
UTC+10:30	LHST	Lord Howe Island
UTC+11	NCT	Noumea , Magadan, Solomon Islands, Honiara
UTC+12	NZST	Auckland , Wellington, Fiji, Suva, Christchurch, Kamchatka
UTC+12:45	CHAST	Chatham Islands
UTC+13	TOT	Nuku'alofa , Apia, Tonga, Samoa
UTC+14	LINT	Kiritimati , Christmas Island

$ man utc-offsets

How UTC Offsets Work

UTC offsets indicate the difference between local time and Coordinated Universal Time:

Positive offsets (UTC+X) — Local time is ahead of UTC. When it's 12:00 UTC, it's 17:00 in UTC+5.
Negative offsets (UTC-X) — Local time is behind UTC. When it's 12:00 UTC, it's 04:00 in UTC-8.
Half-hour offsets (UTC±X:30) — Used by countries like India (UTC+5:30), Iran (UTC+3:30), and Afghanistan (UTC+4:30).
Quarter-hour offsets (UTC±X:45) — Rare offsets used by Nepal (UTC+5:45) and Chatham Islands (UTC+12:45).

$ tz --special

Notable Timezones

UTC-12 (AoE)

"Anywhere on Earth" — The last timezone where any date exists. Used for international deadlines.

UTC+14 (LINT)

Line Islands Time — The first place on Earth to enter a new day. 26 hours ahead of UTC-12.

UTC+0 (GMT)

Greenwich Mean Time — The prime meridian reference, passing through London, UK.

UTC+5:45 (NPT)

Nepal Time — One of only two quarter-hour offsets. Chosen to differentiate from India.

$ faq --timezone

Frequently Asked Questions

[?] What is UTC?

UTC (Coordinated Universal Time) is the primary time standard by which the world regulates clocks and time. It is the successor to Greenwich Mean Time (GMT) and is used as the basis for civil time worldwide. UTC does not observe daylight saving time.

[?] How do UTC offsets work?

UTC offsets indicate how many hours ahead (+) or behind (-) a timezone is from UTC. For example, UTC+5 means the local time is 5 hours ahead of UTC, while UTC-8 means it's 8 hours behind. Some regions use half-hour (UTC+5:30) or quarter-hour (UTC+5:45) offsets.

[?] Why are there half-hour and quarter-hour timezones?

Some countries adopted non-standard offsets to better align their civil time with solar noon. India uses UTC+5:30, Nepal uses UTC+5:45, and Australia's Northern Territory uses UTC+9:30. These offsets reflect historical, political, or geographical considerations.

[?] How many timezones are there?

There are 37 distinct UTC offsets in use worldwide, ranging from UTC-12 (Baker Island) to UTC+14 (Line Islands, Kiribati). This includes standard hour offsets plus several half-hour and quarter-hour variations.

[?] What is the International Date Line?

The International Date Line runs roughly along the 180° longitude line in the Pacific Ocean. When crossing westward, you add a day; when crossing eastward, you subtract a day. This is why UTC+14 and UTC-12 can exist simultaneously.

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