Time ZonesHalf-hour and quarter-hour time zones
Most of the world keeps a time that differs from UTC by a whole number of hours. A handful of countries and regions do not: their clocks sit on the half hour or, in a few cases, on the quarter hour. India is by far the largest of them.
Every such offset in use
This table is worked out from the current rules in the time zone database. The "sun-time line" is the longitude at which that offset matches the sun exactly.
| Offset | Used in | Sun-time line | People in towns of 15,000+ |
|---|---|---|---|
| UTC−9:30 | Marquesas, French Polynesia | 142.5° west | no town that large |
| UTC−3:30 | St Johns, Canada (part of the year) | 52.5° west | 202,000 |
| UTC−2:30 | St Johns, Canada (part of the year) | 37.5° west | 202,000 |
| UTC+3:30 | Iran | 52.5° east | 50 million |
| UTC+4:30 | Afghanistan | 67.5° east | 8.8 million |
| UTC+5:30 | India, Sri Lanka | 82.5° east | 361 million |
| UTC+5:45 | Nepal | 86.2° east | 5.9 million |
| UTC+6:30 | Myanmar, Cocos Islands | 97.5° east | 18 million |
| UTC+8:45 | Eucla, Australia | 131.2° east | no town that large |
| UTC+9:30 | Adelaide, Australia (part of the year), Darwin, Australia, Broken Hill, Australia (part of the year) | 142.5° east | 1.8 million |
| UTC+10:30 | Adelaide, Australia (part of the year), Broken Hill, Australia (part of the year), Lord Howe, Australia (part of the year) | 157.5° east | 1.6 million |
| UTC+12:45 | Chatham, New Zealand (part of the year) | 191.2° east | no town that large |
| UTC+13:45 | Chatham, New Zealand (part of the year) | 206.2° east | no town that large |
Why not just use a whole hour?
A whole-hour zone is centred on a line of longitude that is a multiple of 15 degrees: 60°, 75°, 90° east and so on. A country whose middle falls halfway between two such lines has an awkward choice. India's central line, 82.5° east, is exactly halfway between 75° and 90°. Taking UTC+5 would put the clock well behind the sun in the east of the country, and UTC+6 would put it well ahead in the west. UTC+5:30 splits the difference.
The quarter hours
Nepal goes one step finer. Its time, UTC+5:45, is set close to the longitude of its own mountains, a little east of Kathmandu, which also keeps Nepal's clock fifteen minutes apart from India's. The Chatham Islands of New Zealand keep a time 45 minutes ahead of the mainland, and a small stretch of roadhouses around Eucla in Australia keeps a local time on the quarter hour between the western and central states.
Half an hour of summer time
Lord Howe Island, off the east coast of Australia, is unusual in another way: it moves its clocks by 30 minutes for summer and not by a full hour, going from UTC+10:30 to UTC+11.
Does it cause problems?
For people living there, none at all: a clock is a clock. The trouble comes only when converting. Software that assumes whole hours gets these places wrong, and people working sums in their heads often forget the extra thirty minutes. A safe habit is to convert through UTC: India is UTC+5:30, so 3:00 pm in India is 9:30 am UTC, and from there to any other place is a simple step. Or let the converter do it.
See all offsets, whole and fractional, on the UTC offsets page.