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

No. The gap stays at 2h all year.

When is the best time to call Karachi from Bangkok?

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

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

Bangkok

Thailand

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Karachi

Pakistan

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

City	Time zone	UTC offset
Bangkok · Thailand	Asia/Bangkok	UTC+7
Karachi · Pakistan	Asia/Karachi	UTC+5

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