There is no overlap between 09:00–18:00 working days in these two places.
How many hours is CST behind IST?
As abbreviations, IST is always 11.5 hours ahead of CST: CST is UTC−6 and IST is UTC+5:30. To convert, add 11.5 hours.
When the CST to IST time difference changes
For most of the year IST is 10.5 hours ahead of CST. From 1 November to 31 December 2026, IST is 11.5 hours ahead of CST 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
IST vs CST
Length
1 November 2026 to 31 December 2026
11.5 hours ahead
61 days
1 January 2027 to 13 March 2027
11.5 hours ahead
72 days
14 March 2027 to 6 November 2027
10.5 hours ahead
238 days
7 November 2027 to 31 December 2027
11.5 hours ahead
55 days
Calling hours for CST and IST
When IST is 10.5 hours ahead of CST: no shared 09:00 to 17:00 hours; try 07:00 in CST (17:30 in IST).
When IST is 11.5 hours ahead of CST: no shared 09:00 to 17:00 hours; try 07:00 in CST (18:30 in IST).
Frequently asked questions about CST and IST time
How many hours ahead is IST of CST?
IST (UTC+5:30) is 11.5 hours ahead of CST (UTC−6).
Does the time difference between CST and IST change?
Yes. It is usually 10.5 hours ahead, but changes when one side moves its clocks: 11.5 hours ahead from 1 November to 31 December 2026; 11.5 hours ahead from 1 January to 13 March 2027.