The United States uses nine standard time zones when its territories are included: Atlantic, Eastern, Central, Mountain, Pacific, Alaska, Hawaii-Aleutian, Samoa, and Chamorro. The 50 states themselves span six of them, from Eastern Time on the East Coast to Hawaii-Aleutian Time in Hawaii.
Most of the country observes daylight saving time in spring, summer, and fall, and time zone boundaries are regulated by the U.S. Department of Transportation.