Chicago and London Time Zone Comparison
The distance between Chicago and London is felt not just in kilometers, but in time zones too. Chicago and London sit on different continents, in noticeably different time zones, and at least one of them observes daylight saving time.
Chicago is always 6 hours behind London, with no seasonal change, since neither city's daylight saving rules shift this relationship.
With a moderate gap like this, it's worth checking the suggested call window above before scheduling a meeting between Chicago and London.