India is 4.5 or 5.5 hours ahead of the United Kingdom, depending on the season. The United Kingdom follows Greenwich Mean Time, or GMT, in the winter and British Summer Time, or BST, during daylight savings time. India follows India Standard Time, or IST, the entire year.
IST is UTC +5:30 throughout the year, since India does not observe daylight savings time. BST offsets Coordinated Universal Time, or UTC, by adding an hour at the start of daylight savings time, which begins on the last Sunday of March and ends the last Sunday of October.
According to Time and Date, GMT came into use in Great Britain to standardize clocks for the railroads. Most railroads began using GMT by 1847. Public clocks started using GMT during the mid-19th century, and the legal system in Britain started using GMT in 1880.
In 1884 India had two major time zones: Bombay Time and Calcutta Time. The standardized IST came into existence in 1905. Bombay Time, 39 minutes behind IST, continued in use until 1955.