Thailand follows UTC+7, which is seven hours ahead of Greenwich Mean Time and Coordinated Universal Time. The local mean time in Bangkok was originally GMT+06:42:04. Thailand used this local mean time until 1920, when it changed to Indochina Time, GMT+07:00.
|Period in use
||Time offset from GMT
||Name of time (unofficial)
|1 January 1880 - 31 March 1920
||Bangkok Mean Time
|1 April 1920 – present
||Indochina Time (ICT)
Standardisation of time in Thailand
Thailand declared that people would move their clocks ahead by 17 minutes, 56 seconds to match the time in use in Southeast Asia (UTC+06:42:04 hrs and UTC+07:00:00 ahead of Greenwich Mean Time) on 31 March 1920. The time was switched on 1 April 1920 at 06:00 (old time) to 06:17:56 (new time).
On 1 January 1990, the Thai cabinet appointed the Royal Thai Navy as the official timekeeper for Thailand. Thai Standard Time is derived from five atomic clocks maintained by the Royal Thai Navy.