IST — India Standard Time

India Standard Time (IST) is five and a half hours ahead of Coordinated Universal Time, making it one of the few major time zones with a half-hour offset. IST is used across the entire Republic of India, which spans roughly 30 degrees of longitude from Gujarat in the west to Arunachal Pradesh in the east. The time is calculated based on the longitude 82.5 degrees east, which passes near the city of Mirzapur in Uttar Pradesh.

Despite India's enormous geographic width, the country maintains a single time zone. This has been a subject of ongoing debate, as sunrise and sunset times vary by nearly two hours between the country's eastern and western extremes. Proposals to create a separate time zone for northeastern India have been discussed but never implemented, partly due to concerns about complicating railway schedules and national coordination. India's population of over 1.4 billion people makes IST one of the most widely used time zones in the world by population.

India Standard Time does not observe daylight saving time. DST was briefly used during the Sino-Indian War in 1962 and the Indo-Pakistani Wars of 1965 and 1971 to reduce civilian energy consumption, but it has not been used since. The half-hour offset from neighboring time zones, combined with the country's tropical to subtropical latitude, means that daylight hours do not vary as dramatically as in higher-latitude countries.