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

Yes. Because of daylight saving time the gap moves between −2h and −1h.

When is the best time to call Istanbul from Berlin?

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

Berlin is 1h behind Istanbul. This gap is not fixed: daylight saving time moves it between −2h and −1h during the year.

Berlin

Germany

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Istanbul

Türkiye

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A 9-to-5 day in each city overlaps for 7h. That is 09:00–16:00 in Berlin, which is 10:00–17:00 in Istanbul.

City	Time zone	UTC offset
Berlin · Germany	Europe/Berlin	UTC+2
Istanbul · Türkiye	Europe/Istanbul	UTC+3

What is the time difference between Berlin and Istanbul?: Berlin is 1h behind Istanbul. This gap is not fixed: daylight saving time moves it between −2h and −1h during the year.
Does the time difference between Berlin and Istanbul change during the year?: Yes. Because of daylight saving time the gap moves between −2h and −1h.
When is the best time to call Istanbul from Berlin?: Between 09:00 and 16:00 in Berlin, which is 10:00 to 17:00 in Istanbul.