India's time zone is UTC/GMT (Coordinated Universal Time/Greenwich Mean Time) +5.5 hours. It's referred to as Indian Standard Time (IST).
What's unusual is that there is only one time zone across the whole of India. The time zone is calculated according to the longitude of 82.5° E. at Shankargarh Fort in Mirzapur (in the Allahabad district of Uttar Pradesh), which was picked as the central meridian for India. It's also important to note is that Daylight Saving Time doesn't operate in India.
Time Differences Between Various Countries.
In general, without taking into account Daylight Saving Time, the time in India is 12.5 hours ahead of the west coast of the USA (Los Angeles, San Fransisco, San Diego), 9.5 hours ahead of the east coast of the USA (New York, Florida), 5.5 hours ahead of the UK, and 4.5 hours behind Australia (Melbourne, Sydney, Brisbane).
History of India's Time Zone
Time zones were officially established in India in 1884, during British rule. Two time zones were used -- Bombay Time and Calcutta Time -- due to the importance of these cities as commercial and economic centers. In addition, Madras Time (set up by astronomer John Goldingham in 1802) was followed by many railway companies.
IST was introduced on January 1,1906. However, Bombay Time and Calcutta Time continued to be maintained as separate time zones until 1955 and 1948 respectfully, after India's Independence.
Although India currently doesn't observe Daylight Saving Time, it did briefly exist during the Sino-Indian War in 1962 and the India-Pakistan Wars in 1965 and 1971, in order to reduce civilian energy consumption.
Issues with India's Time Zone
India is a large country. At its widest point, it stretches for 2,933 kilometers (1,822 miles) from Arunachal Pradesh in the east to Gujarat in the west, and covers almost 30 degrees of longitude. According to convention, each time zone in the world is spaced by 15 degrees longitude. Hence, India could have two time zones.
However, the government chooses to keep a single time zone across the whole country (similar to China), despite various requests and proposals to change it. This means that the sun rises and sets almost two hours earlier on India's eastern border than in the Rann of Kutch in the far west.
In many places in India, the sun rises and sets much earlier than official working hours. Sunrise is as early as 4 a.m. and sunset by 4 p.m. in northeast India, resulting in a loss of daylight hours and productivity. In particular, this creates a major issue for tea growers in Assam.
To combat this, Assam's tea gardens follow a separate time zone known as Tea Garden Time or Bagantime, which is one hour ahead of IST. Laborers generally work in the tea gardens from 9 a.m. (IST 8 a.m.) to 5 p.m. (IST 4 p.m.). This system was introduced during British rule, keeping in mind the early sunrise in this part of India.
The Assam government wants to introduce the separate time zone across the whole state and the other northeast Indian states. A campaign was started in 2014 but it's yet to be approved by the Central Government of India. The government is keen to retain one time zone to prevent confusion and safety issues (such as in regards to railway operations and flights).
The issue of India's time zone came up again in 2018, with the publication of a paper by scientists from the Council of Scientific & Industrial Research-National Physical Laboratory in the October 2018 edition of Current Science. The paper argues for a separate time zone of UTC+6.5 hours for the states of Assam, Meghalaya, Nagaland, Arunanchal Pradesh, Manipur, Mizoram, Tripura, and the Andaman and Nicobar Islands.
Another study by a research scholar at Cornell University, published in January 2019, estimates that India's single time zone causes it to incur annual human capital costs of about $4.1 billion (nearly 29,000 crore rupees) or 0.2% of nominal Gross Domestic Product.