Highlighted rows fall within 09:00–18:00 in both places: 4 shared working hours.
How many hours is IST ahead of BST?
As abbreviations, BST is always 4.5 hours behind of IST: IST is UTC+5:30 and BST is UTC+1. To convert, subtract 4.5 hours.
When the IST to BST time difference changes
For most of the year BST is 4.5 hours behind of IST. From 25 October to 31 December 2026, BST is 5.5 hours behind of IST instead, because the two places change their clocks on different dates. Meetings booked by the usual gap land an hour off in those weeks.
Dates
BST vs IST
Length
29 March 2026 to 24 October 2026
4.5 hours behind
210 days
25 October 2026 to 31 December 2026
5.5 hours behind
68 days
1 January 2027 to 27 March 2027
5.5 hours behind
86 days
28 March 2027 to 30 October 2027
4.5 hours behind
217 days
31 October 2027 to 31 December 2027
5.5 hours behind
62 days
Calling hours for IST and BST
When BST is 4.5 hours behind of IST: 3 shared office hours, 14:00 to 17:00 in IST (09:30 to 12:30 in BST).
When BST is 5.5 hours behind of IST: 2 shared office hours, 15:00 to 17:00 in IST (09:30 to 11:30 in BST).
Frequently asked questions about IST and BST time
How many hours ahead is BST of IST?
BST (UTC+1) is 4.5 hours behind of IST (UTC+5:30).
Does the time difference between IST and BST change?
Yes. It is usually 4.5 hours behind, but changes when one side moves its clocks: 5.5 hours behind from 25 October to 31 December 2026; 5.5 hours behind from 1 January to 27 March 2027.