How Time Zones Work (and Why They’re Not Always a Whole Hour Apart)
Time zones are loosely based on 15° slices of longitude, but country borders bend that pattern — which is why a few places sit 30 or even 45 minutes off from their neighbors.
In principle, the Earth is divided into 24 time zones, each roughly 15° of longitude wide, so that solar noon falls near midday in each zone. In practice, time zone boundaries follow country and sometimes state borders instead of pure longitude lines — which is why the map of time zones looks far messier than a clean set of vertical stripes.
Not every offset is a whole hour
Most time zones sit at a whole-hour offset from UTC, but not all of them. A few countries use a half-hour or even a quarter-hour offset:
- India (Asia/Kolkata) is UTC+5:30.
- Nepal (Asia/Kathmandu) is UTC+5:45.
These aren’t rounding quirks — they’re deliberate national choices, often made so the whole country shares one time despite spanning a wide range of longitude, or to keep the offset from a large neighboring country’s time zone slightly distinct.
This is also why Timemazone stores every location by its IANA time zone identifier (like Asia/Kathmandu) rather than a plain "+5:45" offset — the identifier is the actual source of truth, and the offset is simply derived from it for the date you’re looking at.