The continental United States (the 48 contiguous states) is divided into 4 time zones.

• Eastern Standard Time, 5 hours behind Greenwich Mean Time (GMT). Example city: New York
• Central Standard Time, 6 hours behind GMT. Example city: Chicago
• Mountain Standard Time, 7 hours behind GMT. Example city: Denver
• Pacific Standard Time, 8 hours behind GMT. Example city: Los Angeles
• Alaska and Hawaii have their own time zones: Alaska Standard Time (AKST) and Hawaii Standard Time (HST) ) respectively.

Current time in the four US time zones (covering the 48 contiguous states), Daylight Saving Time (DST) automatically calculated

Daylight Saving Time begins for most of the United States at 2 a.m. on the second Sunday of March. Time reverts to standard time at 2 a.m. on the first Sunday of November.

Daylight Saving Time, for the U.S. and its territories, is NOT observed in Hawaii, American Samoa, Guam, Puerto Rico, the Virgin Islands and the state of Arizona (not the Navajo Indian Reservation, which does observe DST). Navajo Nation participates in the Daylight Saving Time policy, due to its large size and location in three states.

GMT/UTC offset, state by state

Official Reference: UNITED STATES CODE, TITLE 15 - COMMERCE AND TRADE, CHAPTER 6 - WEIGHTS AND MEASURES AND STANDARD TIME, SUBCHAPTER IX - STANDARD TIME

Useful tools for multiple time zones