London is 6 hours ahead of Chicago most of the year, and 5 hours from mid-March to late March and from late October to early November.
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Quick reference
| LONDON | CHICAGO · MOST OF THE YEAR | CHICAGO · MID-MAR–LATE MAR, LATE OCT–EARLY NOV |
|---|---|---|
| 9:00 am | 3:00 am | 4:00 am |
| 12:00 pm | 6:00 am | 7:00 am |
| 3:00 pm | 9:00 am | 10:00 am |
| 6:00 pm | 12:00 pm | 1:00 pm |
| 9:00 pm | 3:00 pm | 4:00 pm |
Questions
6 hours most of the year, and 5 hours from mid-March to late March and from late October to early November, when London and Chicago change their clocks on different dates.
3am most of the year, and 4am from mid-March to late March and from late October to early November.
Yes, both, on different dates. London moves to BST (UTC+1) in late March and back to GMT (UTC+0) in late October; Chicago moves to CDT (UTC-5) in mid-March and back to CST (UTC-6) in early November.