India is five and a half hours ahead of UTC. Not five, not six. Anybody in India has spent their whole life adding halves, and it is easy to assume the rest of the world does the same.
It does not. Of the 418 time zones a browser knows about, 15 are currently offset by something other than a whole hour, and India is by far the largest of them.
The awkward ones
Most of the fifteen are on a half hour. Three are not on a half hour either. The table below lists places rather than zones, and has fewer rows than fifteen because some offsets cover more than one — Adelaide, Broken Hill and Darwin all share +9:30.
| Place | Offset | Note |
|---|---|---|
| India | +5:30 | The one most people have to deal with |
| Sri Lanka | +5:30 | The same offset as India |
| Nepal | +5:45 | Fifteen minutes ahead of India |
| Iran | +3:30 | |
| Afghanistan | +4:30 | |
| Myanmar | +6:30 | |
| Eucla, Australia | +8:45 | A tiny settlement on the Nullarbor |
| Darwin and Adelaide | +9:30 | Adelaide also changes its clocks |
| Lord Howe Island | +10:30 | And moves by 30 minutes, not 60 |
| Chatham Islands | +12:45 | Furthest from a whole hour |
| Newfoundland | -2:30 | In summer; -3:30 in winter |
| Marquesas Islands | -9:30 |
Nepal is the one that surprises people who already know about India. It is not half an hour from anything. It is forty-five minutes, deliberately set fifteen minutes ahead of Indian time.
Nepal is not an hour from India, or half an hour. It is fifteen minutes.
What breaks
A meeting planner that draws a grid of hours has to put every city in a column. If the columns are anchored on London, India does not land on them — every Indian row reads half past.
The lazy fix is to round, and it is always wrong by up to 45 minutes. The honest fix is to show the real local time on each row, even when it is not a neat hour, and to draw the line where a city changes date at the place it actually falls rather than at the nearest column edge.
You can spot which kind you are using in about ten seconds. Put New Delhi and London in the same planner. If the Indian row reads whole hours, the tool has rounded your country off and you should not trust the answer to the minute.
Why any of this exists
Time zones are decided by governments, not by geometry. A half-hour offset is usually a country splitting the difference between two neighbours, or picking the time that best matches the sun over the middle of its territory.
They also change. Countries have moved between offsets, adopted daylight saving and dropped it again, and skipped a day entirely to cross the date line. That is why the count above is a measurement from a particular week rather than a fact, and why software should read the rules rather than store them.