EST vs EDT
When each label is correct, how long each season lasts and what changes at the switch.
Basics · Abbreviations
Eastern Time abbreviations
ET names the zone, EST (UTC−5) its winter time and EDT (UTC−4) its summer time. The other labels you will meet, from EWT and EPT to HNE, Romeo and America/New_York, describe the same clocks from another era, language or system.
- In use right now
- EST or EDT
- Generic label
- ET
- IANA zone
- America/New_York
- French (Canada)
- HNE / HAE
What do ET, EST and EDT stand for?
| Label | Stands for | Offset | Where it belongs |
|---|---|---|---|
| ET | Eastern Time | UTC−5 or UTC−4 | Anything not tied to one date |
| EST | Eastern Standard Time | UTC−5 | Dates from the first Sunday in November to the second Sunday in March |
| EDT | Eastern Daylight Time | UTC−4 | Dates from the second Sunday in March to the first Sunday in November |
| EWT | Eastern War Time | UTC−4 | February 9, 1942 – August 14, 1945 |
| EPT | Eastern Peace Time | UTC−4 | August 14 – September 30, 1945 |
| EPT | Eastern Prevailing Time | whichever is in force | US electricity markets and energy contracts |
| HE · HNE · HAE | heure de l'Est · heure normale · heure avancée de l'Est | either · UTC−5 · UTC−4 | French-language text in Canada |
| R · Q | Romeo · Quebec | UTC−5 · UTC−4 | Military time zone letters |
America/New_York | IANA zone ID | rules, not an offset | Software, calendars, databases |
EST5EDT | POSIX-style zone name | UTC−5 / UTC−4 | Legacy Unix settings |
Only the first three are in everyday use. EST and EDT are season-specific, while ET never is; the rule for choosing between them is laid out in EST vs EDT, and each one gets its own page, EST and EDT. The current label also shows on the live Eastern Time clock.
What were Eastern War Time and Eastern Peace Time?
From 2:00 AM on February 9, 1942, the United States kept its clocks one hour ahead all year as a wartime measure, and in the East the advanced time was called Eastern War Time. When Japan's surrender was announced on the evening of August 14, 1945, at 7:00 PM EWT (23:00 UTC), the same clocks were relabelled Eastern Peace Time, and radio announcers began giving the time as "Eastern Peace Time". EPT lasted only until September 30, 1945, when clocks fell back to EST.
Both labels survive in the tz database, so Unix tools still print a July 1943 timestamp for America/New_York as EWT and a September 1945 one as EPT. Today EPT usually means something else: Eastern Prevailing Time, a term from US electricity markets. PJM, the grid operator for the Mid-Atlantic region and beyond, labels its schedules and hourly data in EPT, and energy contracts define it as EST or EDT, whichever is in effect. In other words, EPT is the power industry's ET.
What do America/New_York, America/Toronto and EST5EDT mean?
Software does not run on abbreviations; it uses zone identifiers from the IANA time zone database, named after a representative city. America/New_York covers most of the US Eastern zone and America/Toronto covers the Eastern parts of Ontario and Quebec, with America/Montreal and America/Nassau kept as aliases of it. Detroit, Indianapolis, Louisville and Iqaluit have IDs of their own because their clocks had different histories, even though they follow the same rules today.
Older Unix systems also accept EST5EDT, a POSIX-style name that applies US federal rules and assumes standard time existed forever, and plain EST, a fixed UTC−5 zone with no daylight saving, the trap described on the EST page. Microsoft Windows uses a third vocabulary: its zone ID "Eastern Standard Time" means the whole Eastern zone, daylight saving included, and maps to America/New_York.
The short labels you see on screen are generated from the zone ID and your language setting. In US English America/New_York appears as EST or EDT and in Canadian French as HNE or HAE, while British English and German settings fall back to "GMT-5" or "GMT-4". How offsets are written and stored is covered in the UTC offset guide.
How is Eastern Time abbreviated in French?
In Quebec and in French-language federal texts, Eastern Time is l'heure de l'Est (HE). Standard time is l'heure normale de l'Est (HNE) and daylight time is l'heure avancée de l'Est (HAE): "advanced" time, the same word the US federal rules use when standard time "shall be advanced 1 hour". The Office québécois de la langue française advises adding the abbreviation after a clock time only when the context needs that precision, and French typography writes the hour with an h, so 9:30 AM EDT becomes 9 h 30 HAE. The Montreal page shows the live time in Canada's largest French-speaking city.
What do R, Q and "8/7c" mean?
Military time zones use a letter for each whole-hour offset, so a time can be tagged with a single character: Z (Zulu) is UTC, R (Romeo) is UTC−5 and Q (Quebec) is UTC−4. Because each letter is a fixed offset, EST is R and EDT is Q: 9:00 AM EDT is 0900Q, or 1300Z. Much military and aviation traffic avoids the question by using Z throughout; the notation is explained in the military time guide.
Television has its own shorthand. "8/7c" means a programme airs at 8:00 PM Eastern and 7:00 PM Central on the same national feed. The West Coast usually gets a delayed feed at 8:00 PM Pacific, and Mountain-zone times vary by network, so viewers there should check local listings.
Which time zone abbreviations are ambiguous?
Abbreviations are not unique, and several collide with North American ones:
- CST: Central Standard Time (UTC−6), China Standard Time (UTC+8), 14 hours apart, and the label the tz database uses for Cuba's standard time.
- IST: India Standard Time (UTC+5:30), Irish Standard Time (Ireland's summer time, UTC+1) or Israel Standard Time (UTC+2).
- BST: British Summer Time (UTC+1) or Bangladesh Standard Time (UTC+6).
- AST: Atlantic Standard Time (UTC−4) or Arabia Standard Time (UTC+3).
For an international audience, pair the label with an offset, as in 9:00 AM ET (UTC−4), or give the time in UTC. The glossary defines UTC, GMT and the other terms used here.
Which Eastern Time abbreviation should you use?
AP style, followed by most US newsrooms, capitalises the full names, Eastern Standard Time and Eastern Daylight Time, and lowercases the short form: Eastern time, the Eastern time zone. It accepts EST or EDT on first reference only when attached to a clock reading, as in "noon EST" or "9 a.m. EDT". Beyond the newsroom, match the label to the reader:
- Invitations and schedules that span seasons: ET, as in "Mondays, 10:00 AM ET".
- International readers: ET plus the offset, or UTC.
- French-language Canada: HNE or HAE, or simply HE.
- Code, calendars and APIs:
America/New_YorkorAmerica/Toronto, never "EST". - Military and aviation: Z, or R and Q.
- Energy contracts: EPT, with hour-ending numbering.
Frequently asked questions
What does “EST/EDT” with a slash mean?
It means whichever of the two applies, which is exactly what ET means. It is common on forms and in software menus. For a single dated event, write the one actually in force.
Is AEST the same as EST?
No. AEST is Australian Eastern Standard Time, UTC+10, used in Brisbane all year and in Sydney and Melbourne outside their summer. It is 15 hours ahead of EST. The tz database labelled Australia's eastern zone EST until 2014, which still trips up old software.
Is EET related to Eastern Time?
No. EET is Eastern European Time, UTC+2 (EEST, UTC+3, in summer), used in places such as Greece, Finland and Ukraine. It is 7 hours ahead of EST.
What does HE mean in an EPT schedule?
Hour ending. Power markets number the hours of the day 1 to 24 by the clock time at which they end, so HE1 is 12:00 to 1:00 AM EPT and HE24 is 11:00 PM to midnight. The day EDT begins has only 23 hourly intervals and the day it ends has 25.
Explore
Military time
24-hour notation and the full set of zone letters from A to Z.
Glossary
Short definitions of UTC, GMT, local mean time, IANA zones and more.
Time in Montreal
Live time in the city where Eastern Time is written HNE and HAE.