History

• In the U.S. and Canada, time zones were first established on November 18, 1883, as a means of standardizing railroad arrivals and departures. Early versions of the time zones we know today, including Eastern Standard and Pacific Standard, were created with the Standard Time Act of 1918.
  
  

Geography

• Eastern and Pacific time zones differ first in their geography. In the United States, the Eastern time zone encompasses the entire eastern seaboard and mid-eastern states like Michigan, Ohio and Indiana, as well as eastern sections of both Kentucky and Tennessee. The Pacific time zone comprises the three westernmost states, California, Oregon and Washington, as well as Nevada.
  
  

Time Differences

• There is a standardized three-hour time difference between Eastern and Pacific time zones. Eastern time is calculated by subtracting 5 hours from Universal Time, Coordinated (UTC), while Pacific time is calculated by subtracting 8 hours from UTC.
  
  

Daylight Saving Time

• Both Eastern and Pacific time zones are subject to daylight saving time, becoming the Eastern Daylight and Pacific Daylight zones for eight months of the year. During this period, the Eastern Daylight time is UTC minus 4 hours, while Pacific Daylight is UTC minus 7.
  
  

Arizona

• The state of Arizona is one of only two states that does not recognize daylight saving time and so, for eight months out of the year, Arizona's time is in sync with the Pacific time zone at UTC minus 7.