Which zone this page means. IST means India Standard Time (UTC+5:30), Irish Standard Time (UTC+1) and Israel Standard Time (UTC+2). This page means the Indian zone, which is one of the few on a half-hour offset. 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.
IST is ahead of BST by 4.5 hours today
On 19 August 2026, India Standard Time is on IST at UTC+05:30 and British Summer Time is on BST at UTC+01:00. The gap between them is 4.5 hours, with BST behind. So 9:00 am in IST is 4:00 am in BST, and 5:00 pm in IST is 12:00 pm in BST. Going the other way, see BST to IST.
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. India Standard Time does not observe daylight saving, so the gap moves only when British Summer Time 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 IST that window runs from 2:00 pm to 5:00 pm, which is 9:00 am to 12:00 pm in BST. 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 4.5-hour gap above.