A timezone labelled CST — why do some people read US Central Time?

Question

Weirdo · Accepted Answer

CST is not a unique timezone id. North American Central Standard Time is UTC−6; UTC+8 is also written CST in Chinese usage. IANA wants Asia/Shanghai, Asia/Taipei, or America/Chicago — never three letters as the only key.

IANA’s tz page says alphabetic abbreviations should not be unique identifiers for UT offsets because they collide in practice. In English-speaking North America, CST is six hours behind UT; in China it is eight hours ahead. The theory file lists CST/CDT twice: Central [North America] and China. Same three letters, fourteen hours apart.

The stable identifiers are place names: America/Chicago (US Central, CST in winter / CDT in summer), Asia/Shanghai (China Standard Time, also abbreviated CST), and Asia/Taipei for Taiwan. Application writers are told outright that CST means one thing in China and another in North America; use a numeric offset such as −0600, or store the IANA name. A meeting invite or log that only says CST will be read in Chicago more often than you want.

A timezone labelled CST — why do some people read US Central Time?

Three letters, two places

Store Asia/Taipei, not CST