Which zone this page means. GMT and UTC are the same offset but not the same thing: GMT is a time zone, UTC is a time standard. The United Kingdom is on GMT in winter and BST (UTC+1) in summer. CST means US Central Standard Time (UTC-6) and also China Standard Time (UTC+8) — fourteen hours apart. This page means the US zone. For the Chinese zone see China Standard Time.
GMT is ahead of CST by 5 hours today
On 19 August 2026, Greenwich Mean Time is on GMT at UTC+00:00 and Central Standard Time (US) is on CDT at UTC-05:00. The gap between them is 5 hours, with CST behind. So 9:00 am in GMT is 4:00 am in CST, and 5:00 pm in GMT is 12:00 pm in CST. Going the other way, see CST to GMT.
The gap is not constant, and that is the part that catches people out
Central Standard Time (US) is currently observing daylight saving and changes next on 1 November 2026. Greenwich Mean Time does not observe daylight saving, so the gap moves only when Central Standard Time (US) changes its clocks — twice a year, by one hour.
When you can actually both be at work
Taking a working day as 9:00 am to 5:00 pm local at each end, there are 3 overlapping hours in a normal day. In GMT that window runs from 2:00 pm to 5:00 pm, which is 9:00 am to 12:00 pm in CST. Anything outside it needs one side to start early or finish late.
Zone rules are set by legislation and change, sometimes at short notice. This page is built against tzdata 2026a, last reviewed 2026-08-18. Quarterly. Zone rules change by legislation, sometimes at short notice. Version and review date are shown on every zone page. The converter above reads your browser's own copy of the zone database, so if a rule has changed since this page was built the live answer follows the new rule.
Every convention used above — whether the start date counts, how month ends are clamped, which holidays close an office — is written out on the methodology page, including the daylight-saving rules behind the 5-hour gap above.