Does the time difference between Berlin and Chicago change during the year?

Yes. Because of daylight saving time the gap moves between +6h and +7h.

When is the best time to call Chicago from Berlin?

Between 16:00 and 17:00 in Berlin, which is 09:00 to 10:00 in Chicago.

Berlin is 7h ahead of Chicago. This gap is not fixed: daylight saving time moves it between +6h and +7h during the year.

Berlin

Germany

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Chicago

United States

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A 9-to-5 day in each city overlaps for 1h. That is 16:00–17:00 in Berlin, which is 09:00–10:00 in Chicago.

City	Time zone	UTC offset
Berlin · Germany	Europe/Berlin	UTC+2
Chicago · United States	America/Chicago	UTC−5

What is the time difference between Berlin and Chicago?: Berlin is 7h ahead of Chicago. This gap is not fixed: daylight saving time moves it between +6h and +7h during the year.
Does the time difference between Berlin and Chicago change during the year?: Yes. Because of daylight saving time the gap moves between +6h and +7h.
When is the best time to call Chicago from Berlin?: Between 16:00 and 17:00 in Berlin, which is 09:00 to 10:00 in Chicago.