The time zones that are not on the hour

By Niraj Kumar · Published October 28, 2026

The idea that the world is divided into twenty-four one-hour slices is a useful fiction. Offsets from UTC are set by governments, not geography, and about a dozen of them end in :30 or :45. More than a billion and a half people live in them. The time zone list shows every current offset; this guide explains where the odd ones come from and what they mean for anyone working with time.

The half-hour zones

India (UTC+05:30) is the largest. Before standardisation, Bombay and Calcutta each kept local mean time, about an hour apart. The compromise meridian chosen in 1906, 82.5° east, lay halfway between them and is exactly five and a half hours ahead of Greenwich. Sri Lanka returned to the same offset in 2006 after a decade at +06:00 and +06:30.

Iran (UTC+03:30) uses the meridian of 52.5° east, which runs close to Tehran. It observed daylight saving until 2022, when the change was abolished, so it now keeps +03:30 all year.

Afghanistan (UTC+04:30) and Myanmar (UTC+06:30) likewise took the meridian nearest their capitals rather than rounding to the hour. The Cocos (Keeling) Islands share Myanmar’s offset. Newfoundland (UTC−03:30) is the only half-hour zone in the Americas; it was set to the local mean time of St John’s before the province joined Canada in 1949 and was never changed. It observes daylight saving, so it is −02:30 in summer.

Central Australia (UTC+09:30), covering South Australia and the Northern Territory, sits between the eastern states at +10:00 and Western Australia at +08:00. South Australia observes daylight saving and becomes +10:30 in summer; the Northern Territory does not. The Marquesas Islands in French Polynesia keep UTC−09:30.

The quarter-hour zones

Nepal (UTC+05:45) is the best known. The country chose the meridian of Gaurishankar, a Himalayan peak at roughly 86.25° east, as its reference in 1986, placing it fifteen minutes ahead of India. The choice was partly symbolic: a distinct time was a distinct identity.

The Chatham Islands (UTC+12:45), 800 kilometres east of New Zealand, keep forty-five minutes ahead of the mainland, and follow its daylight saving, so they reach UTC+13:45 in summer, the largest offset in the world that is not a whole hour.

Eucla (UTC+08:45) is the strangest case: a strip of the Nullarbor on the border between Western and South Australia whose few hundred residents keep a time of their own, halfway between the two states. It has never been recognised in law. It is in the IANA database under Australia/Eucla because people genuinely use it.

Zones that have come and gone

Odd offsets appear and disappear with politics. Venezuela moved from −04:00 to −04:30 in 2007 and back in 2016. North Korea moved to +08:30 in 2015 and back to +09:00 in 2018 to match the South. Until the 1940s the Netherlands kept UTC+00:19:32, the mean time of Amsterdam, and Liberia used −00:44:30 until 1972. Historical dates in these places need the historical rule, which is the reason the time zone database records every change since 1970 and many before.

What this means for software

Any code that stores an offset as a whole number of hours is wrong for a fifth of humanity. An offset needs minutes, and ISO 8601 writes it that way: +05:30, +05:45. Any dropdown that lists “GMT+5” and “GMT+6” with nothing between them cannot represent India. Any scheduling algorithm that steps through zones an hour at a time will skip Kathmandu. The practical rule is to never compute with offsets at all: name the zone, Asia/Kolkata or Asia/Kathmandu, and let the database supply the offset for the date in question. The time difference tool is a quick way to see that Mumbai to London is five and a half hours in winter and four and a half in summer.

Why not just round

Each of these offsets was a rational choice at the time. The meridian halfway across a country minimises how far the clock is from the sun at either edge; a country that spans two whole-hour zones but wants one national time will often land in the middle. India’s single zone means the sun rises in the north-east nearly two hours before it does in the west, and there have been proposals for a second zone or a move to +06:00, none adopted. The offsets persist because changing a national clock is disruptive and the benefits of a round number are small. As a rule, the stranger an offset looks, the more deliberately it was chosen.

Checking your own tools

Open any world clock or scheduler you rely on and add Kathmandu. If it shows the correct quarter-hour offset, it handles minutes; if it shows +05:00 or +06:00, it does not, and anything it says about India, Iran or Newfoundland is also suspect. The world clock here is built on the IANA database and shows all of them correctly, including Chatham’s summer +13:45.