One country, one zone. India runs every clock from the 82.5°E meridian near Mirzapur, Uttar Pradesh, a line chosen in 1906 because it sat roughly central to the population centres of undivided India. The result: a single IANA identifier, Asia/Kolkata, for all 28 states and 8 union territories. No second zone exists. No legislative change is pending for 2026 or 2027.
What is Asia/Kolkata?
Asia/Kolkata is the only IANA time zone entry for India. It covers New Delhi, the national capital, and every other city. There is no Asia/Mumbai, Asia/Chennai, or Asia/Guwahati identifier. The single-zone policy is legally enforced under the Indian Standard Time Act and the Legal Metrology Act.
| Attribute | Value |
|---|---|
| IANA identifier | Asia/Kolkata |
| Time zone name | India Standard Time (IST) |
| UTC offset | UTC+5:30 |
| DST observed | None |
| Geographic coverage | All of India |
| Number of IANA zones for India | 1 |
Why is India UTC+5:30 with no DST?
India Standard Time stays fixed at UTC+5:30 every day of the year. The country has never adopted daylight saving time outside of British wartime rule (1942-1945). No DST bill is active in 2026 or 2027.
The half-hour offset puts India in a small group of nations using a :30 marker. Others include Iran, Afghanistan, and Myanmar.
Time differences from New Delhi (IST) on 15 January 2026:
| Location | Time difference |
|---|---|
| New York | 10.5 hours behind |
| London | 5.5 hours behind |
| Dubai | 1.5 hours behind |
| Singapore | 2.5 hours ahead |
| Tokyo | 3.5 hours ahead |
| Sydney | 5.5 hours ahead |
Time differences from New Delhi (IST) on 15 July 2026:
| Location | Time difference |
|---|---|
| New York | 9.5 hours behind |
| London | 4.5 hours behind |
| Dubai | 1.5 hours behind |
| Singapore | 2.5 hours ahead |
| Tokyo | 3.5 hours ahead |
| Sydney | 4.5 hours ahead |
The summer-to-winter gap in US and UK offsets reflects their own DST shifts. India's offset never moves.
Why was Asia/Calcutta renamed to Asia/Kolkata?
Before 2008, the IANA identifier was Asia/Calcutta. The database maintainers renamed it to Asia/Kolkata to match the city's official name change from Calcutta to Kolkata, formalised in 2001. The old identifier Asia/Calcutta remains in the IANA database as a link (alias) pointing to Asia/Kolkata. Systems using the old name still function but should be updated.
The reference longitude for IST, 82.5°E, passes through Mirzapur, Uttar Pradesh. British India adopted this single standard on 1 January 1906, replacing a patchwork of Madras Time (UTC+5:21:14), Calcutta Time (UTC+5:53:20), and Bombay Time (UTC+4:51).
Which states and territories fall under Asia/Kolkata?
All of them. India spans roughly 29 degrees of longitude, yet every territory uses the same zone. The solar time difference between the eastern and western extremes approaches two hours.
Tea gardens in Assam often unofficially operate on "Chaibagan Time" (UTC+6:30), one hour ahead of IST, to use daylight better. This is a local, non-statutory practice.
How does Asia/Kolkata compare to neighbouring zones?
| Country | IANA zone | UTC offset | Notes |
|---|---|---|---|
| India | Asia/Kolkata | UTC+5:30 | No DST |
| Sri Lanka | Asia/Colombo | UTC+5:30 | Same offset, separate legal standard |
| Nepal | Asia/Kathmandu | UTC+5:45 | 15 minutes ahead of IST |
| Pakistan | Asia/Karachi | UTC+5:00 | 30 minutes behind IST |
| Bangladesh | Asia/Dhaka | UTC+6:00 | 30 minutes ahead of IST |
| Bhutan | Asia/Thimphu | UTC+6:00 | 30 minutes ahead of IST |
Sri Lanka Standard Time shares the same UTC offset as IST but is independently maintained by Sri Lanka's time authority.
Using Asia/Kolkata in code and scheduling tools
Always use Asia/Kolkata when programming or scheduling. Avoid Asia/Calcutta. Avoid the bare abbreviation "IST", which is ambiguous: it also means Irish Standard Time (UTC+1, summer) and Israel Standard Time (UTC+2, winter). In international tools, "IST" alone causes misalignment.
For a deeper explanation of why India sticks to one zone despite its size, read the full breakdown of India's single time zone policy. To understand the historical time zones that preceded IST, see the history of Madras, Bombay, and Calcutta Time.