Time Zone Confusion?

May 1, 2018

Eastern Standard Time is the designation of the timezone of the eastern seaboard of the United States. It is the second time zone of the United StatesThe first timezone is Atlantic standard time followed by eastern, central, mountain, Pacific, Alaska, Hawaii-Aleutian, Samoa, and Chamorro and is retarded by 5 hours from Coordinated Universal Time (UTC), except as provided by 15 U.S.C. § 260a, which specifies that in the period commencing at 2 o’clock antemeridian on the second Sunday of March and ending at 2 o’clock antemeridian on the first Sunday of November, the standard time zones are advanced by one hour. So during that period“daylight saving time”, eastern standard time is defined as being retarded by four instead of five hours from UTC. 15 U.S.C. §§ 261-264.

Hence it is always correct to indicate time as being EST regardless of the daylight saving status since it is the offset that changes, not the designation.

The designation of EDT, or eastern daylight time is helpful when computing the difference in time between locations in different time zones. For example, the difference between UTC and EST may be 5 or 4 hours depending on the time of year. The difference between UTC and EDT will always be 4 hours, though EDT doesn’t exist outside of the daylight saving time period.