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

No. The gap stays at 1h all year.

When is the best time to call Beijing from Bangkok?

Between 09:00 and 16:00 in Bangkok, which is 10:00 to 17:00 in Beijing.

Bangkok is 1h behind Beijing. This gap is the same all year — neither city shifts its clocks relative to the other.

Bangkok

Thailand

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Beijing

China

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

City	Time zone	UTC offset
Bangkok · Thailand	Asia/Bangkok	UTC+7
Beijing · China	Asia/Shanghai	UTC+8

What is the time difference between Bangkok and Beijing?: Bangkok is 1h behind Beijing. This gap is the same all year — neither city shifts its clocks relative to the other.
Does the time difference between Bangkok and Beijing change during the year?: No. The gap stays at 1h all year.
When is the best time to call Beijing from Bangkok?: Between 09:00 and 16:00 in Bangkok, which is 10:00 to 17:00 in Beijing.