Time zones can be confusing. You can thank our ancestors and poor policy for most of the headaches we have when it comes to time zones. The below aims to clear up some confusion about time zones and aid in the understanding of how time zones affect dates and times.
A time zone really refers to a place. When you are talking about when something occurred, it is also important to talk about where it occurred. An event happens in time and in space. Time zones are divisions of the Earth's surface into distinct regions, each of which observes a standardized time offset from Coordinated Universal Time (UTC) or Greenwich Mean Time (GMT). The primary purpose of time zones is to account for the Earth's rotation, which causes different parts of the world to experience daylight and nighttime at different times. Time zones are used for coordination, international communication, tracking daylight and work hours, and accurate timekeeping.
Most of the contiguous United States uses four large time zones. Eastern, Central, Mountain and Pacific. Alaska and Hawaii use their own zones. There several smaller parts of the US that use their own rules.
Due to several issues with the four familiar zones, they are not officially recognized in the time zone database which is used by most computer programs and operating systems. America/New_York, America/Chicago, America/Denver and America/Los_Angeles are some of the timezones used by computers. There are hundreds of time zones around the world.
By itself, ‘UTC’ stands for Coordinated Universal Time and is a time standard by which the world regulates clocks and time. It was standardized and adopted around the globe in the 1960s. When most people say UTC time, they are referring to the time zone that the UTC standard is based off of, sometimes written as UTC+00:00. Many time zones can be written with an hour and minute offset from UTC. UTC-07:00 is Mountain Standard Time. The UTC+00:00 time zone is the same as the Greenwich Mean Time (GMT) time zone. Greenwich, England, is a district located in the southeastern part of London and has played a significant role in the measurement and tracking of time throughout history. The Royal Observatory and the Prime Meridian are in Greenwich where GMT was developed; hence the name Greenwich Mean Time. Zulu time is the name the US army gave GMT and is often denoted with a Z, e.g. '2027-09-20T20:29:39.078Z'. Zulu, GMT and UTC time almost always refer to the same zone and are often used interchangeably. Almost all computers store and use UTC time internally. This provides standardization, global compatibility and consistency.
Some regions within time zones also observe daylight saving time or British summer time, where clocks are adjusted forward in the Spring and back in the Fall. Daylight saving is not a time zone. Daylight saving is intended to make better use of daylight during certain seasons possibly resulting in energy conservation and improved productivity. The Eastern, Central, Mountain and Pacific time zones observe daylight saving. Arizona, Hawaii, Alaska, some U.S. territories, and parts of Indiana do not observe daylight saving time.
Jan 4, 2026 5:05 am EST
The above date says EST meaning eastern standard time. The important part of EST or EDT (Eastern Daylight Time) is just the eastern time zone part and not the daylight or standard part. Daylight Saving Time (DST) in most of the United States starts on the second Sunday in March and ends on the first Sunday in November. Because January 4 is not during daylight savings, we know January 4 is during the standard time part of the year. The ‘ST’ or ‘DT’ in time zone names is only used as a convenience so humans are aware of whether or not January 4 is within the part of the year that observes daylight saving or not.
EST is 5 hours behind Coordinated Universal Time (UTC-5). Jan 4, 2026 10:05 am UTC is the equivalent representation in the UTC+00:00 time zone
Pacific Standard Time (PST): the time zone that is 8 hours behind Coordinated Universal Time (UTC-8). It is the standard time zone for the western part of the United States and Canada
Local time: refers to the current time zone you are in.
Time zones are a standardized way to account for the Earth's rotation, allowing people around the world to coordinate activities, communicate internationally, and maintain consistent schedules. They play a crucial role in modern life, ensuring that time is kept in an orderly and predictable manner across different geographic regions.