How many time zones does the US have?

The US has six time zones across the 50 states: Eastern (UTC-5), Central (UTC-6), Mountain (UTC-7), Pacific (UTC-8), Alaska (UTC-9), and Hawaii-Aleutian (UTC-10). US territories add several more, including Atlantic (UTC-4) for Puerto Rico and the US Virgin Islands, Chamorro (UTC+10) for Guam, and Samoa Standard Time (UTC-11) for American Samoa.

Why does Arizona not observe daylight saving time?

Arizona opted out of DST in 1968 because the extra evening daylight would extend the hottest part of the day, increasing air-conditioning costs and making outdoor activity uncomfortable. The Navajo Nation within Arizona does observe DST, while the Hopi Reservation within the Navajo Nation does not, creating a nested patchwork.

What law governs US time zones?

The Uniform Time Act of 1966 established the system of standardized time zones and DST rules across the United States. It allows states to exempt themselves from DST by state legislation but does not permit them to observe DST year-round without federal approval.

US Time Zones Explained

May 28, 2026

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Frequently Asked Questions

How many time zones does the US have?: The US has six time zones across the 50 states: Eastern (UTC-5), Central (UTC-6), Mountain (UTC-7), Pacific (UTC-8), Alaska (UTC-9), and Hawaii-Aleutian (UTC-10). US territories add several more, including Atlantic (UTC-4) for Puerto Rico and the US Virgin Islands, Chamorro (UTC+10) for Guam, and Samoa Standard Time (UTC-11) for American Samoa.
Why does Arizona not observe daylight saving time?: Arizona opted out of DST in 1968 because the extra evening daylight would extend the hottest part of the day, increasing air-conditioning costs and making outdoor activity uncomfortable. The Navajo Nation within Arizona does observe DST, while the Hopi Reservation within the Navajo Nation does not, creating a nested patchwork.
What law governs US time zones?: The Uniform Time Act of 1966 established the system of standardized time zones and DST rules across the United States. It allows states to exempt themselves from DST by state legislation but does not permit them to observe DST year-round without federal approval.