Daylight saving time in the United States
Time Zone Standard Time Daylight Saving Time TZ
Atlantic Time Zone AST ( UTC−04:00 ) ADT ( UTC−03:00 ) AST4ADT
Eastern Time Zone EST ( UTC−05:00 ) EDT ( UTC−04:00 ) EST5EDT
Central Time Zone CST ( UTC−06:00 ) CDT ( UTC−05:00 ) CST6CDT
Mountain Time Zone MST ( UTC−07:00 ) MDT ( UTC−06:00 ) MST7MDT
Pacific Time Zone PST ( UTC−08:00 ) PDT ( UTC−07:00 ) PST8PDT
Alaska Time Zone AKST ( UTC−09:00 ) AKDT ( UTC−08:00 ) AKST9AKDT
Hawaii-Aleutian Time Zone HST ( UTC−10:00 ) HDT ( UTC−09:00 ) Aleutian Islands only HST10HDT
Time zones
This article may require cleanup to meet Wikipedia 's quality standards . The specific problem is : Crude System-V style time-zone specifiers have fallen out of favor because they can not express more complicated rules , and they leave ambiguous the date and time of the switch , which is often the thing that changes most . As a result , most modern operating systems use the Olson timezone specifiers like America/New_York or US/Eastern rather than EST5EDT . Please help improve this article if you can . ( May 2019 ) ( Learn how and when to remove this template message )
Daylight saving time in the United States is the practice of setting the clock forward by one hour during the warmer part of the year, so that evenings have more daylight and mornings have less. Most areas of the United States and Canada observe daylight saving time (DST), the exceptions being Arizona (except for the Navajo, who do observe daylight saving time on tribal lands), Hawaii, and the overseas territories of American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the United States Virgin Islands. The Uniform Time Act of 1966 established the system of uniform Daylight Saving Time throughout the US. In the U.S., daylight saving time starts on the second Sunday in March and ends on the first Sunday in November, with the time changes taking place at 2:00 a.m. local time. With a mnemonic word play referring to seasons, clocks spring forward, fall back - that is, in springtime the clocks are moved forward from 2:00 a.m. to 3:00 a.m. and in fall they are moved back from 2:00 a.m. to 1:00 a.m. Daylight saving time lasts for a total of 34 weeks (238 days) every year, about 65% of the entire year. The following table lists recent past and near future starting and ending dates of daylight saving time in North America: