Which zone this page means. BST means British Summer Time (UTC+1) and also Bangladesh Standard Time (UTC+6). This page means the British zone, which applies from the last Sunday in March to the last Sunday in October; the rest of the year the United Kingdom is on GMT. 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.
BST is ahead of GMT by 1 hours today
On 19 August 2026, British Summer Time is on BST at UTC+01:00 and Greenwich Mean Time is on GMT at UTC+00:00. The gap between them is 1 hours, with GMT behind. So 9:00 am in BST is 8:00 am in GMT, and 5:00 pm in BST is 4:00 pm in GMT. Going the other way, see GMT to BST.
The gap is not constant, and that is the part that catches people out
British Summer Time is currently observing daylight saving and changes next on 25 October 2026, when clocks go back an hour. Greenwich Mean Time does not observe daylight saving at all, so the whole of the seasonal change comes from the BST side: the gap moves by an hour twice a year even though nothing changes in Greenwich Mean Time.
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 7 overlapping hours in a normal day. In BST that window runs from 10:00 am to 5:00 pm, which is 9:00 am to 4:00 pm in GMT. 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 1-hour gap above.