Why time zones exist
Time zones exist because different parts of the world experience daylight at different times as the Earth rotates. Rather than every location using solar time exactly, most of the world is divided into standardized zones, each offset from Coordinated Universal Time (UTC) by a fixed (or seasonally variable) number of hours.
How UTC offsets work
Every time zone is expressed as an offset from UTC — for example, India Standard Time (IST) is UTC+5:30. Unlike most time zones which use whole-hour offsets, India uses a half-hour offset, which occasionally causes confusion when converting to or from zones that only shift in whole hours.
Daylight Saving Time (DST)
Some countries shift their clocks forward by an hour during part of the year (typically spring to autumn) to make better use of daylight — this is Daylight Saving Time. India does not observe DST, but many countries you might schedule calls or travel with do, which means the effective time difference between India and those countries can change twice a year even though India’s own offset never changes.
Why this trips people up
- A meeting time converted correctly in January may be an hour off by July if the other country has since started or ended DST.
- Calendar invites created without an explicit time zone can display differently to recipients in different zones.
- “GMT” and “UTC” are often used interchangeably in casual speech but are not always precisely identical.
Practical tip
For any recurring international meeting or deadline, it’s safer to reconfirm the local time close to the date rather than assuming a fixed offset calculated months earlier still holds.