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

No. The gap stays at 2h all year.

When is the best time to call Karachi from Istanbul?

Between 09:00 and 15:00 in Istanbul, which is 11:00 to 17:00 in Karachi.

Istanbul is 2h behind Karachi. This gap is the same all year — neither city shifts its clocks relative to the other.

Istanbul

Türkiye

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Karachi

Pakistan

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A 9-to-5 day in each city overlaps for 6h. That is 09:00–15:00 in Istanbul, which is 11:00–17:00 in Karachi.

City	Time zone	UTC offset
Istanbul · Türkiye	Europe/Istanbul	UTC+3
Karachi · Pakistan	Asia/Karachi	UTC+5

What is the time difference between Istanbul and Karachi?: Istanbul is 2h behind Karachi. This gap is the same all year — neither city shifts its clocks relative to the other.
Does the time difference between Istanbul and Karachi change during the year?: No. The gap stays at 2h all year.
When is the best time to call Karachi from Istanbul?: Between 09:00 and 15:00 in Istanbul, which is 11:00 to 17:00 in Karachi.