Greenwich Mean Time (GMT) is the mean solar time at the Royal Greenwich Observatory in Greenwich near London, England, which by convention is at 0 degrees geographic longitude. Theoretically, noon Greenwich Mean Time is the moment when the Sun crosses the Greenwich meridian (and reaches its highest point in the sky in Greenwich).

To convert from GMT add the value shown in the table below for the local time zone. Convert to GMT by subtracting the value.

Time Zone	Offset	Daylight Savings
EST (New York)	-5 hours	EDT	-4 hours
CST (Chicago)	-6 hours	CDT	-5 hours
MST (Denver)	-7 hours	MDT	-6 hours
PST (Los Angeles)	-8 hours	PDT	-7 hours

For all of Greater China, GMT remains 7 hours before Beijing time all year around. Thus, 7 AM in Beijing is midnight in Greenwich mean time. While DST is in force for the US, the time in Beijing is exactly twelve hours ahead of New York time.

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