Three abbreviations, two offsets
The Eastern zone of the United States has two offsets from UTC. In winter it runs on Eastern Standard Time, EST, which is UTC−5. From the second Sunday in March to the first Sunday in November federal law advances the clocks one hour, and the zone runs on Eastern Daylight Time, EDT, which is UTC−4. ET, Eastern Time, is the name of the zone itself. It does not say which offset applies; the date does. In 2026 daylight time runs from March 8 to November 1, so a time written in ET means EDT on any day in between and EST on the rest.
That is why ET is the safe choice for anything that recurs or that people read without checking the calendar: "Support hours are 9:00 a.m. to 5:00 p.m. ET" is right in every month. "9:00 a.m. EST" is right only from November to March. The same pattern holds for the other zones: CT, MT and PT each stand for a standard and a daylight abbreviation.
The US zones
| Zone | Standard | Daylight | Write | Cities | IANA name |
|---|---|---|---|---|---|
| Eastern | EST (UTC−5) | EDT (UTC−4) | ET | New York, Miami, Atlanta | America/New_York |
| Central | CST (UTC−6) | CDT (UTC−5) | CT | Chicago, Dallas, Houston | America/Chicago |
| Mountain | MST (UTC−7) | MDT (UTC−6) | MT | Denver, Salt Lake City | America/Denver |
| Arizona (Mountain, no DST) | MST (UTC−7) | none | MST | Phoenix | America/Phoenix |
| Pacific | PST (UTC−8) | PDT (UTC−7) | PT | Los Angeles, Seattle | America/Los_Angeles |
| Alaska | AKST (UTC−9) | AKDT (UTC−8) | AKT | Anchorage | America/Anchorage |
| Hawaii (no DST) | HST (UTC−10) | none | HST | Honolulu | Pacific/Honolulu |
Hawaii and most of Arizona do not change their clocks, so their abbreviation is the same all year and there is no generic form to worry about. Arizona shares the Mountain zone, which means Phoenix matches Denver in winter and Los Angeles in summer. The Navajo Nation inside Arizona does observe daylight time. American Samoa, Guam, Puerto Rico and the Virgin Islands stay on standard time as well. The daylight saving time 2026 guide has the dates for every country that changes its clocks, and UTC and time zones explained covers what the offsets mean.
The same moment in every zone
A call at 2:00 p.m. Eastern lands at these local times, computed from the offsets above. The gaps between the US zones do not change with the season, because they all switch on the same day, except Arizona and Hawaii, which are one hour closer to the rest of the country in summer.
| Zone | Summer (EDT, UTC−4) | Winter (EST, UTC−5) |
|---|---|---|
| Eastern | 2:00 p.m. EDT | 2:00 p.m. EST |
| Central | 1:00 p.m. CDT | 1:00 p.m. CST |
| Mountain | 12:00 p.m. MDT | 12:00 p.m. MST |
| Arizona (Mountain, no DST) | 11:00 a.m. MST | 12:00 p.m. MST |
| Pacific | 11:00 a.m. PDT | 11:00 a.m. PST |
| Alaska | 10:00 a.m. AKDT | 10:00 a.m. AKST |
| Hawaii (no DST) | 8:00 a.m. HST | 9:00 a.m. HST |
The time zone converter does this for any date and any pair of cities, and it applies the daylight rules of both places, which matters when one of them is outside the US and switches on a different day.
When to write ET, EST or EDT
- ET for anything that spans the year: business hours, a weekly meeting, a published schedule, a support page, a contract. The reader applies the offset for the date.
- EDT or EST for a single moment where you want to leave no doubt which offset applies: a deadline on a particular day, a log entry, a timestamp in a report. Then the abbreviation must match the date. From March 8 to November 1, 2026 it is EDT; the rest of the year EST.
- A numeric offset for anything a machine or a reader abroad will process: 2:00 p.m. ET (UTC−4). The IANA time zone database recommends numeric offsets precisely because abbreviations are ambiguous.
The mistake that shows up most often is "EST" used as if it were the name of the zone. In July the Eastern zone is on EDT, so "3:00 p.m. EST" on a July date names a time that is an hour later than 3:00 p.m. in New York. Most readers quietly correct it. A calendar app or a converter does not: it takes EST as UTC−5 and shows the wrong hour.
An invite that survives the clock change
A meeting time written as text has to carry three things: the date, the local time, and the zone. The zone should be a name, not a fixed offset, because a fixed offset is only right for part of the year. A line that works:
The date fixes which offset ET means; the UTC offset in parentheses lets anyone check it; the second city and the UTC time spare the reader a conversion. For a recurring meeting, drop the offset and keep the zone name, since the offset will change in November while the ET time stays the same. The meeting planner lays several cities side by side for a given date and shows which hours fall inside working time for everyone, which is the quickest way to pick the slot before you write it down.
Two cases need extra care. First, a meeting between a US city and one abroad in the weeks when only one side has switched: the US changes on the second Sunday in March and the first Sunday in November, and other countries change on other dates or not at all, so the usual gap is off by an hour for a while. Second, a recurring meeting set up in a fixed offset rather than a zone, which drifts by an hour for half the year. Setting the meeting in the zone of the organizer avoids both.
America/New_York and the IANA names
Software does not store "ET". It stores an identifier from the IANA time zone database, which has the form area/location: a continent or ocean, then a city, as in America/New_York, America/Chicago, America/Denver, America/Los_Angeles, America/Phoenix for Arizona, America/Anchorage and Pacific/Honolulu. The database deliberately uses cities rather than countries, so that the names survive a change of a country's name or borders. Each entry carries the whole history of offsets and clock changes for that location, which is how a phone shows the right hour for a date in any month, past or future. When a form, an API or a configuration file asks for a time zone, this is the name to give it. The time zone converter works from these names as well.
Abbreviations that mean two things
Abbreviations are not unique. The IANA documentation lists several that collide across countries and recommends numeric offsets instead:
| Abbreviation | Can mean |
|---|---|
| CST | Central Standard Time in North America, and China Standard Time |
| IST | India, Ireland (Irish Standard Time) or Israel |
| BST | British Summer Time, and the historical Bering Standard Time |
"10:00 a.m. CST" sent to a supplier in Shanghai and a colleague in Chicago names two moments fourteen hours apart. Where a reader might be outside the US, add the offset or a city: "10:00 a.m. CT (Chicago, UTC−5)".
Checklist
- Recurring or year-round: ET, CT, MT, PT.
- One specific moment: EDT or EST matching the date, or ET with the UTC offset in parentheses.
- Readers abroad or software: add the numeric UTC offset or the IANA name.
- Arizona and Hawaii: no daylight time, so MST and HST all year.
- Before you send: check the date against March 8 and November 1, 2026, and run the time through the time zone converter.
Frequently asked questions
What is the difference between EST, EDT and ET?
EST is Eastern Standard Time, UTC−5, in effect from November to March. EDT is Eastern Daylight Time, UTC−4, in effect from the second Sunday in March to the first Sunday in November. ET is the Eastern time zone without saying which of the two applies, and it is the right choice whenever the date decides the offset.
Is it wrong to write EST in summer?
Yes, strictly speaking. From the second Sunday in March to the first Sunday in November the Eastern zone runs on EDT, UTC−4. Writing 2:00 p.m. EST in July names a time that is one hour off from the clocks in New York. Readers usually guess what you meant, but a time zone converter or a calendar app takes EST literally.
Which US states do not observe daylight saving time?
Hawaii and most of Arizona stay on standard time all year, as do American Samoa, Guam, Puerto Rico and the Virgin Islands. The Navajo Nation inside Arizona does change its clocks. Federal law lets a state exempt itself as long as the whole state, or the whole part of it in one zone, stays on standard time.
When does daylight saving time start and end in the US?
At 2:00 a.m. local time on the second Sunday in March and at 2:00 a.m. on the first Sunday in November. In 2026 that is March 8 and November 1. The rule is in 15 USC 260a, and standard time is advanced one hour for that period.
What is America/New_York?
The name of the Eastern zone in the IANA time zone database, which operating systems, phones and most software use to convert times. Names have the form area/location, with a continent or ocean and a city, so that the name stays valid when a country or its borders change. The database knows every past and future clock change for the location, so a time stored with this name converts correctly in any month.
Sources
- 15 U.S. Code § 260a, Advancement of time or changeover dates (standard time advanced one hour from 2 a.m. on the second Sunday of March to 2 a.m. on the first Sunday of November; a state may exempt itself by law)
- NIST, Daylight Saving Time (2026 dates March 8 and November 1; not observed in Hawaii, American Samoa, Guam, Puerto Rico, the Virgin Islands and Arizona, except the Navajo Nation)
- NIST and USNO, time.gov (the standard time abbreviations and UTC offsets of the US zones: EST −5, CST −6, MST −7, PST −8, AKST −9, HST −10, Arizona on MST)
- IANA Time Zone Database, Theory and pragmatics (names in the form AREA/LOCATION such as America/New_York, tied to cities rather than countries; abbreviations are ambiguous, CST in China and North America, IST in India, Ireland or Israel; numeric offsets recommended)