India has one time zone for the whole country. It is called India Standard Time, or IST, and runs at UTC+5:30. India does not change its clocks for daylight saving.
One country, one clock
According to timeanddate.com, India has only one time zone, and there are no daylight saving clock changes.
That means an office in Delhi and an office in Chennai run on the same time, all year.
How India’s time was set
The path to one clock took some time.
- In 1905, a meridian near Mirzapur, at 82°33′E, was chosen as the national standard.
- UTC+5:30 has been used as local standard time since 1906.
- India Standard Time was declared the official time in 1947.
- Calcutta Time stayed in use until 1948, and Bombay Time until 1955.
Why one clock is not simple
India is almost 3,000 kilometres wide and spans nearly 30 degrees of longitude. According to timeanddate.com, if India set its time zones by mean solar time, it would have three. With one clock, the Sun rises almost 90 minutes earlier in far-east Dong than in Guar Mota in the west.
India has not always had one clock. In 1884, two zones were in use, Calcutta Time and Bombay Time, just over an hour apart.
In 2018, India’s CSIR-National Physical Laboratory and National Measurement Institute proposed two zones. They were IST-I (UTC+5:30) and IST-II (UTC+6:30) in the northeast. timeanddate.com says this has yet to be legally formalized.
The tea garden clock in Assam
One informal exception exists. In Assam, tea gardens use Tea Garden Time, an unofficial zone one hour ahead of IST, at UTC+6:30. British tea companies introduced it to make better use of daylight for working hours. timeanddate.com says it is still used.
Other places with half-hour zones
A few places set clocks 30 or 45 minutes off the usual whole-hour zones. According to timeanddate.com:
- Sri Lanka uses UTC+5:30, the same as India.
- Nepal uses UTC+5:45.
- Afghanistan uses UTC+4:30.
- Myanmar uses UTC+6:30.
- The Northern Territory in Australia uses UTC+9:30.
