Why some countries have half-hour time zones
Updated 2026-09-19
Most time zones are a whole number of hours away from UTC. A few are not: India is UTC+5:30, Nepal is UTC+5:45, and South Australia is UTC+9:30 in winter. These are deliberate choices, not mistakes.
Time zones are a decision, not a law of nature
As a rule of thumb, every 15 degrees of longitude is one hour of solar time. But each country decides its own official time. Some pick the whole-hour zone nearest to them, some match a neighbour or a trading partner, and some choose a half-hour offset because it fits their position better.
India, for example, uses one time zone for the whole country, based on 82.5 degrees east, roughly its middle. That longitude works out to exactly 5 hours 30 minutes ahead of UTC.
Where you will find them
Half-hour offsets include India (UTC+5:30), Sri Lanka (UTC+5:30), Afghanistan (UTC+4:30), Iran (UTC+3:30) and Myanmar (UTC+6:30). Nepal uses UTC+5:45, a 45-minute offset chosen to sit close to solar time in Kathmandu.
Some countries have them only in part. Adelaide and South Australia use UTC+9:30, and Newfoundland in Canada uses UTC−3:30.
What they do to your conversions
India does not change its clocks, so London and Mumbai are 5 hours 30 minutes apart in winter and 4 hours 30 minutes in summer, when London moves forward. Manila, at UTC+8, is a steady 2 hours 30 minutes ahead of Mumbai all year, because neither city changes its clocks.
Adelaide shows how a half-hour zone can flip sides. Brisbane stays on UTC+10 all year. Adelaide is 30 minutes behind Brisbane in winter, but during Australian summer time it moves to UTC+10:30 and is 30 minutes ahead.
Let the converter do the arithmetic
The half hours are easy to miscount by hand. The converters below use your browser's time zone data, so the offsets and daylight saving changes are handled for you.