Time in Vietnam

Reunified Vietnam follows Indochina Time (ICT), which is seven hours ahead of UTC, ICT is used all year round as Vietnam does not observe daylight saving time. Vietnam shares the same time zone with Thailand, Cambodia, Christmas Island, Laos, and Western Indonesia.

Vietnam referenced ISO 8601 under in 1998 and then created its own standard TCVN 6398-1:1998.^[1]

History

After Phủ Liễn Observatory was built, French Indochina announced all states (consisting of north-Vietnamese
Guangzhouwan) were part of 104°17′17″E longitude east of Paris meridian 2°20′14″E, or 106°37′30″E from Greenwich Mean Time
from 00:00, 1 July 1906 onward.

In 1911,
UTC±00:00 (the solar time of Greenwich) as its official time, and used it until 1940 (with UTC+01:00
used during the summers from 1916 to 1940), forcing French Indochina observed UTC+07:00 from 00:00, 1 May 1911.

Following change in time zone of Vichy authorities, French Indochina was integrated to UTC+08:00 skipping 60 minutes at 23:00, 31 December 1942.
The Empire of Japan occupied Vichy French Indochina fully. Indochinese regions thereafter followed Tokyo time zone (UTC+09:00), skipping 60 minutes at 23:00, 14 March 1945.
By
Democratic Republic of Vietnam took control, announcing UTC+07:00 as official time zone on 2 September 1945. Whilst, the then under-attack regions of Vietnam, Laos and Cambodia adopted UTC+08:00 and non-attacked regions (at the time and even after the 1954 Geneva Conference) adopted UTC+07:00 from April 1
, 1947: Laos (part of Indochina) from 15 April 1954, Hanoi from October 1954, Haiphong from May 1955.

Under control of State of Vietnam, South Vietnam adopted UTC+07:00 from 00:00, 1 July 1955.
South Vietnam time zone was changed to UTC+08:00 from 23:00, 31 December 1959, passing 60 minutes.
North Vietnam confirmed official UTC+07:00 from 1 January 1968.
Following the
Saigon
(and other southern parts) delaying 60 minutes on 13 June 1975.

Period in use	Time offset from GMT	Notes
Prior to 1 July 1906	UTC+07:06:40	Local mean time
1 July 1906 – 30 April 1911	UTC+07:06:30	106°37'30"E French Time
1 May 1911 – 30 December 1942	UTC+07:00	Standard Time Zone
31 December 1942 – 13 March 1945	UTC+08:00	Standard Time Zone
14 March 1945 – 1 September 1945	UTC+09:00	Tokyo Standard Time
2 September 1945 – Activation of Geneva Accords	UTC+07:00	Standard Time Zone

Period in use	Time offset from GMT	Notes
2 September 1945 – 31 March 1947	UTC+07:00	Hanoi Time Zone
1 April 1947 – Activation of Geneva Accords After the activation	No Standard Time UTC+07:00 for zone under peace UTC+08:00 for zone under attacking
1 January 1968 – 12 June 1975	UTC+07:00	Hanoi Time Zone

Period in use	Time offset from GMT	Notes
Activation of Geneva Accords – 30 June 1955	UTC+08:00	Saigon Standard Time
1 July 1955 – 31 December 1959	UTC+07:00	Saigon Standard Time
1 January 1960 – 12 June 1975	UTC+08:00	Saigon Standard Time

Period in use	Time offset from GMT	Notes
13 June 1975 – now	UTC+07:00	Standard Time Zone

Trần Tiến Bình (2005), Lịch Việt Nam thế kỷ XX-XXI (1901–2100), Nhà xuất bản Văn hoá Thông tin, Hanoi.

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