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The time zones that are not whole hours

Most of the world sits at a whole number of hours from UTC. A meaningful minority does not. India is at UTC+5:30, Nepal at UTC+5:45, and the Chatham Islands at UTC+12:45. These offsets break every mental shortcut and quite a lot of poorly written software.

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Who uses fractional offsets, and why

India adopted UTC+5:30 as a compromise: the country spans about 28 degrees of longitude, roughly two hours of solar time, and a single half-hour offset splits the difference. Sri Lanka follows the same offset. Iran uses UTC+3:30, Afghanistan UTC+4:30, and Myanmar UTC+6:30.

The 45-minute offsets are rarer. Nepal sits at UTC+5:45, deliberately distinct from India. The Chatham Islands sit at UTC+12:45, and Australia's Eucla region at UTC+8:45. Together these account for a few million people, which is enough to matter to any software with international users.

The practical difficulty is that fractional offsets defeat approximations. "India is five and a half hours ahead" is correct, but people round it, and rounding produces a meeting invitation half an hour out. Anything built on integer-hour arithmetic — a spreadsheet formula, a hand-rolled scheduler — will be wrong for a substantial part of the world.

There is also a common bug where a system stores the offset as an integer number of hours. That works everywhere except the places listed above, which is precisely the kind of failure that ships to production and is discovered by a customer in Kathmandu.

Key facts

India and Sri Lanka

UTC+5:30, one offset for the whole country.

Nepal

UTC+5:45, chosen to be distinct from India.

Iran, Afghanistan, Myanmar

UTC+3:30, +4:30 and +6:30 respectively.

Chatham Islands

UTC+12:45, and UTC+13:45 in daylight saving.

Eucla, Australia

UTC+8:45, one of the least populated fractional zones.

Integer-hour code breaks

Storing offsets as whole hours fails for over a billion people.

How to get it right

1

Never assume whole hours

Store offsets in minutes, or better, store the IANA zone.

2

Convert both parts

When doing it by hand, handle the hours and minutes separately.

3

Test with Asia/Kolkata

A half-hour zone catches most integer-hour assumptions.

4

Check the minutes in invitations

A rounded conversion is the usual cause of a half-hour miss.

Questions people ask

Because the country spans roughly two hours of solar time and chose a single central offset. UTC+5:30 splits the difference between its eastern and western extremes.

Keep reading

Daylight saving explained

Which countries change their clocks, when they do it, and why the same two cities can be five hours apart one week and six the next.

UTC, GMT and Zulu time

What UTC actually is, how it differs from GMT, why aviation says Zulu, and when the distinction matters.

Scheduling across time zones

A practical method for booking meetings across zones: finding the overlap, rotating the pain, and stopping recurring calls from drifting.

Convert a half-hour zone

IST pages handle the 30-minute offset exactly, with no rounding.

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