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

Yes. Because of daylight saving time the gap moves between −4h and −3h.

When is the best time to call Karachi from Berlin?

Between 09:00 and 14:00 in Berlin, which is 12:00 to 17:00 in Karachi.

Berlin is 3h behind Karachi. This gap is not fixed: daylight saving time moves it between −4h and −3h during the year.

Berlin

Germany

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Karachi

Pakistan

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A 9-to-5 day in each city overlaps for 5h. That is 09:00–14:00 in Berlin, which is 12:00–17:00 in Karachi.

City	Time zone	UTC offset
Berlin · Germany	Europe/Berlin	UTC+2
Karachi · Pakistan	Asia/Karachi	UTC+5

What is the time difference between Berlin and Karachi?: Berlin is 3h behind Karachi. This gap is not fixed: daylight saving time moves it between −4h and −3h during the year.
Does the time difference between Berlin and Karachi change during the year?: Yes. Because of daylight saving time the gap moves between −4h and −3h.
When is the best time to call Karachi from Berlin?: Between 09:00 and 14:00 in Berlin, which is 12:00 to 17:00 in Karachi.