Indian Standard Time (IST) is the time zone for India. It is 5 hours and 30 minutes ahead of GMT/UTC. The entire country shares the same time. Although using one time universally has its advantages, the drawback is that in places in the far east, the sun rises very early and sets very early, while in the west it rises late and sets late.

The Indian Standard Time is calculated from the Allahabad observatory. Allahabad has 82.5°E longitude which corresponds to an exact 5 hours and 30 minutes difference between India and Greenwich, the reference point for GMT.

India's time zones were established in 1884. However at that time there were two standard time zones, Bombay Time and Calcutta Time. The IST came into effect in 1905. However, Bombay still persisted with its own time zone, 39 minutes behind IST, until 1955.

There is no daylight saving time in India.