America/Chicago

TZ identifier and aliases

America/Chicago is the canonical identifier for US Central Time. Legacy names still pointing at the same rules include US/Central and the POSIX-style CST6CDT, along with a cluster of Indiana and North Dakota county-specific links (America/Indiana/Knox, America/North_Dakota/Center, and others) that historically tracked their own DST decisions before settling on Central Time's rule. All are deprecated in favor of America/Chicago — use the canonical name in new code.

UTC offset and DST rule

Central Time is -06:00 (CST) on standard time and -05:00 (CDT) during daylight saving, following the same nationwide US rule as every other DST-observing US zone: starting the second Sunday in March and ending the first Sunday in November (March 8 and November 1 in 2026). For the rest of the year it sits six hours behind UTC.

Using it in cron, CI and Postgres

Set TZ=America/Chicago for a process that should schedule by Central local time. Postgres handles it natively — SET TIME ZONE 'America/Chicago'; or via the timezone setting — applying the DST rule correctly for any timestamp rather than a fixed offset that goes stale twice a year. Where a scheduler supports it (Vixie-cron and similar), a CRON_TZ=America/Chicago line at the top of a crontab schedules by local time directly; GitHub Actions' schedule: trigger has no such option and always runs in UTC, so a recurring job pinned to a Central-time hour needs its UTC offset recomputed by hand across each DST boundary. Avoid scheduling anything in the 2:00–3:00am local window: that hour doesn't exist on the March transition day, so a matching cron expression silently skips it, and it occurs twice on the November transition, so a naive scheduler can double-fire.

History and quirks

Central Time was one of the four zones the US railroads adopted in 1883 and Congress formalized with the Standard Time Act of 1918. Its internal consistency took much longer than the coastal zones': parts of Indiana and North Dakota within this zone kept their own patchwork DST decisions well into the 2000s, which is why America/Chicago's alias list still carries county-level historical entries even though every one of them now follows identical rules. The zone spans an unusually wide range of longitude — from Chicago out to the Texas Panhandle and western Nebraska, well short of El Paso, which sits far enough west that it instead keeps Mountain Time (America/Denver) — and that western edge periodically debates switching to Mountain Time to better match sunrise/sunset with the business day, a recurring but unresolved discussion in state and county politics rather than an actual tz database change.

Offsets and DST transitions on this page are computed from the IANA time zone database bundled with your browser; the rules described above were verified against tzdata 2026b when this page was published.