Guides
The IANA database, the two-pass conversion, how daylight saving gaps and overlaps are resolved, and exactly what is excluded. Daylight saving changes
Every clock change this year, zone by zone, with the real switch dates and local switch times — and which zones never change at all. IST time difference explained
How far ahead or behind India is from every zone and city, in both seasons, with the exact UTC offsets. Working across the India–US gap
Why a 9–6 Indian day and a 9–5 US day barely touch, where the overlap actually is, and what to do when there is none. The Gulf working week
Saudi Arabia, Qatar and Kuwait run Sunday to Thursday. Against India that is four shared working days, not five. India Standard Time in detail
One zone, UTC+5:30, no daylight saving since 1945 — and why the half-hour offset makes conversions land on :30.
India Standard Time in one paragraph
India Standard Time is UTC+5:30, identified in the IANA time zone database as
Asia/Kolkata. It covers the entire country without exception and has not observed
daylight saving since 1945. That makes IST unusually simple in isolation and unusually awkward in
conversion: the half-hour offset means an Indian hour straddles two clock hours almost everywhere
else, and because India never moves, every seasonal change in the gap comes from the other side.
The three mistakes that produce wrong answers
Converting without a date. Most zones shift by an hour for part of the year, and the switch dates differ by country. A conversion quoted without a date is only right for part of the year. See this year's switch dates.
Treating EST and EDT as interchangeable. They are the two halves of US Eastern Time, an hour apart. The same applies to CST/CDT, MST/MDT and PST/PDT. The EST page resolves whichever is actually in force.
Assuming a shared working week. Saudi Arabia, Qatar, Egypt and Bangladesh run Sunday to Thursday; Nepal runs Sunday to Friday; Iran runs Saturday to Wednesday. Against India's Monday to Friday, some of these share only three or four working days a week.
Frequently asked questions
Why is IST half an hour off from most time zones?
India Standard Time is anchored to the 82.5°E meridian, which sits at UTC+5:30 rather than a whole hour. That is why conversions from IST usually land on :30 rather than :00, and why one Indian hour maps onto two clock hours nearly everywhere else. A handful of other places do the same — Iran at UTC+3:30, Nepal at UTC+5:45, parts of Australia at UTC+9:30.
Does India have more than one time zone?
No. A single zone covers the whole country, from Gujarat to Arunachal Pradesh — roughly 30 degrees of longitude. There is a long-running argument for a second zone in the north-east, where the sun rises around two hours earlier, but none has been adopted.
What is the difference between IST, GMT and UTC?
UTC is the modern reference standard; GMT is the older term for the same UTC+0:00 offset and is still used for civil time in the UK in winter. India is 5 hours 30 minutes ahead of both, always — none of the three observes daylight saving. The UK, however, moves to British Summer Time from late March to late October, which narrows the gap from India to 4 hours 30 minutes.
Why does the gap between India and the US change twice a year?
Because the US changes its clocks and India does not. US Eastern Time is UTC−5:00 in winter and UTC−4:00 in summer, so the gap from India is 10 hours 30 minutes for part of the year and 9 hours 30 minutes for the rest. Europe switches on different dates again, which means the India–US and India–Europe gaps move independently for about two weeks each spring and autumn.
What is a date rollover?
When a conversion crosses midnight. Morning in India is the previous evening across the Americas, and Indian evening is already the next morning in Australia and New Zealand. Every table on this site marks the affected rows with +1 day or −1 day, because booking a meeting on the wrong date is the most common practical error in cross-timezone scheduling.