Asia/Kolkata

Time zone identifier: Asia/Kolkata

Current civil offset: +05:30 (IST)

Current DST state: Observing Standard Time

First standard time adoption: Adopted on 1854-06-27

Local Mean Time (LMT): +05:53:28 based on geographic meridian

Total recorded transitions: 7 transitions across 5 distinct offsets

Associated countries: IN

Aliases (Link targets): Asia/Calcutta

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Historical Offset Step Chart (1880 to Present)

+4:00 +5:00 +6:00 +7:00 +8:00 1880 1900 1920 1940 1960 1980 2000 2020

Text summary: Asia/Kolkata shifted between 5 distinct offsets from 1854-06-27 through the modern era.

Complete Transition History (7 Transitions)

UTC Instant Local Wall Time Shift Abbreviation DST Effect
1854-06-27T18:06:32Z 1854-06-27 23:59:52 +05:53:28 → +05:53:20 HMT No overlap
1869-12-31T18:06:40Z 1869-12-31 23:27:50 +05:53:20 → +05:21:10 MMT No overlap
1905-12-31T18:38:50Z 1906-01-01 00:08:50 +05:21:10 → +05:30 IST No gap
1941-09-30T18:30:00Z 1941-10-01 01:00:00 +05:30 → +06:30 +0630 Yes gap
1942-05-14T17:30:00Z 1942-05-14 23:00:00 +06:30 → +05:30 IST No overlap
1942-08-31T18:30:00Z 1942-09-01 01:00:00 +05:30 → +06:30 +0630 Yes gap
1945-10-14T17:30:00Z 1945-10-14 23:00:00 +06:30 → +05:30 IST No overlap

Notes from the Maintainers

Source: asia (Lines 1248 to 1308)
India

British astronomer Henry Park Hollis disliked India Standard Time's offset:
"A new time system has been proposed for India, Further India, and Burmah.
The scheme suggested is that the times of the meridians 5½ and 6½ hours
east of Greenwich should be adopted in these territories.  No reason is
given why hourly meridians five hours and six hours east should not be
chosen; a plan which would bring the time of India into harmony with
that of almost the whole of the civilised world."
Hollis HP. Universal Time, Longitudes, and Geodesy. Mon Not R Astron Soc.
1905-02-10;65(4):405-6. https://doi.org/10.1093/mnras/65.4.382

From Ian P. Beacock, in "A brief history of (modern) time", The Atlantic
https://www.theatlantic.com/technology/archive/2015/12/the-creation-of-modern-time/421419/
(2015-12-22):
In January 1906, several thousand cotton-mill workers rioted on the
outskirts of Bombay....  They were protesting the proposed abolition of
local time in favor of Indian Standard Time....  Journalists called this
dispute the "Battle of the Clocks."  It lasted nearly half a century.

From Paul Eggert (2017-04-20):
Good luck trying to nail down old timekeeping records in India.
"... in the nineteenth century ... Madras Observatory took its magnetic
measurements on Göttingen time, its meteorological measurements on Madras
(local) time, dropped its time ball on Greenwich (ocean navigator's) time,
and distributed civil (local time)." -- Bartky IR. Selling the true time:
19th-century timekeeping in america. Stanford U Press (2000), 247 note 19.
"A more potent cause of resistance to the general adoption of the present
standard time lies in the fact that it is Madras time.  The citizen of
Bombay, proud of being 'primus in Indis' and of Calcutta, equally proud of
his city being the Capital of India, and - for a part of the year - the Seat
of the Supreme Government, alike look down on Madras, and refuse to change
the time they are using, for that of what they regard as a benighted
Presidency; while Madras, having for long given the standard time to the
rest of India, would resist the adoption of any other Indian standard in its
place." -- Oldham RD. On Time in India: a suggestion for its improvement.
Proceedings of the Asiatic Society of Bengal (April 1899), 49-55.

"In 1870 ... Madras time - 'now used by the telegraph and regulated from the
only government observatory' - was suggested as a standard railway time,
first to be adopted on the Great Indian Peninsular Railway (GIPR)....
Calcutta, Bombay, and Karachi, were to be allowed to continue with their
local time for civil purposes." - Prasad R. Tracks of Change: Railways and
Everyday Life in Colonial India. Cambridge University Press (2016), 145.

Reed S, Low F. The Indian Year Book 1936-37. Bennett, Coleman, pp 27-8.
https://archive.org/details/in.ernet.dli.2015.282212
This lists +052110 as Madras local time used in railways, and says that on
1906-01-01 railways and telegraphs in India switched to +0530.  Some
municipalities retained their former time, and the time in Calcutta
continued to depend on whether you were at the railway station or at
government offices.  Government time was at +055320 (according to Shanks) or
at +0554 (according to the Indian Year Book).  Railway time is more
appropriate for our purposes, as it was better documented, it is what we do
elsewhere (e.g., Europe/London before 1880), and after 1906 it was
consistent in the region now identified by Asia/Kolkata.  So, use railway
time for 1870-1941.  Shanks is our only (and dubious) source for the
1941-1945 data.

Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]

Attributed Statements:

Paul Eggert (2017-04-20):

Good luck trying to nail down old timekeeping records in India. "... in the nineteenth century ... Madras Observatory took its magnetic measurements on Göttingen time, its meteorological measurements on Madras (local) time, dropped its time ball on Greenwich (ocean navigator's) time, and distributed civil (local time)." -- Bartky IR. Selling the true time: 19th-century timekeeping in america. Stanford U Press (2000), 247 note 19. "A more potent cause of resistance to the general adoption of the present standard time lies in the fact that it is Madras time. The citizen of Bombay, proud of being 'primus in Indis' and of Calcutta, equally proud of his city being the Capital of India, and - for a part of the year - the Seat of the Supreme Government, alike look down on Madras, and refuse to change the time they are using, for that of what they regard as a benighted Presidency; while Madras, having for long given the standard time to the rest of India, would resist the adoption of any other Indian standard in its place." -- Oldham RD. On Time in India: a suggestion for its improvement. Proceedings of the Asiatic Society of Bengal (April 1899), 49-55. "In 1870 ... Madras time - 'now used by the telegraph and regulated from the only government observatory' - was suggested as a standard railway time, first to be adopted on the Great Indian Peninsular Railway (GIPR).... Calcutta, Bombay, and Karachi, were to be allowed to continue with their local time for civil purposes." - Prasad R. Tracks of Change: Railways and Everyday Life in Colonial India. Cambridge University Press (2016), 145. Reed S, Low F. The Indian Year Book 1936-37. Bennett, Coleman, pp 27-8. https://archive.org/details/in.ernet.dli.2015.282212 This lists +052110 as Madras local time used in railways, and says that on 1906-01-01 railways and telegraphs in India switched to +0530. Some municipalities retained their former time, and the time in Calcutta continued to depend on whether you were at the railway station or at government offices. Government time was at +055320 (according to Shanks) or at +0554 (according to the Indian Year Book). Railway time is more appropriate for our purposes, as it was better documented, it is what we do elsewhere (e.g., Europe/London before 1880), and after 1906 it was consistent in the region now identified by Asia/Kolkata. So, use railway time for 1870-1941. Shanks is our only (and dubious) source for the 1941-1945 data. Zone NAME STDOFF RULES FORMAT [UNTIL]

Years on Record

Methodology Note: The 1970 Rule

tzdb guarantees accuracy for timestamps from 1970 onwards. Transitions prior to 1970 represent best-effort historical reconstructions.