HDT — Hawaii-Aleutian Daylight Time
See what HDT means, how it relates to HST during daylight saving time, and compare or convert it with other time zones.
How to Convert HDT to Other Time Zones
Open the HDT converter page: Go to https://www.xconvert.com/time-converter/hdt-time-zone to load the visual comparison grid with Hawaii-Aleutian Daylight Time (HDT) as the reference row. This page is useful when you need to line up time in Alaska’s Aleutian communities with offices in North America or Asia, such as planning a fisheries logistics call, airline operations check-in, or a remote support handoff.
Add comparison cities with + Add City: Click “+ Add City” and add places such as Anchorage, Honolulu, and Los Angeles to compare HDT against nearby and mainland business hubs. This is especially practical for shipping, government coordination, and aviation because the Aleutian region often needs to align with Alaska-based administration, Hawaii-based Pacific schedules, and U.S. West Coast operations.
Drag across the grid to select a meeting window: Use Select mode, then drag across the HDT row to highlight a range such as 9:00 AM to 11:00 AM HDT; the purple selection will show the matching local times in every added row. For example, 9:00 AM HDT is 10:00 AM AKDT in Anchorage, 8:00 AM HST in Honolulu, and 12:00 PM PDT in Los Angeles, which quickly shows whether a same-day operational call works across Pacific and Alaska time zones.
Export or share the selected time: After selecting the range, use the export options for ICS download, Google Calendar, Gmail, Copy to clipboard, or Share link. That is useful when sending a confirmed time block to a distributed team, such as a marine supply vendor, airport operations contact, or mainland client, so each recipient sees the event in their own local time automatically.
About Hawaii-Aleutian Daylight Time (HDT)
Hawaii-Aleutian Daylight Time (HDT) is the daylight saving version of the Hawaii-Aleutian time zone, and its exact offset is UTC−09:00. That means HDT is 9 hours behind Coordinated Universal Time, 1 hour ahead of HST (UTC−10:00), and 1 hour behind Alaska Daylight Time (AKDT, UTC−08:00) during the months when daylight saving time is active in the Aleutian portion of Alaska.
HDT is used in the Aleutian Islands portion of Alaska west of 169°30′ west longitude, not in the state of Hawaii. In practice, this includes communities such as Adak, one of the best-known inhabited places in this zone, while Hawaii remains on HST year-round and does not observe daylight saving time. The distinction matters for travel planning, federal scheduling, and military or weather coordination in the North Pacific because “Hawaii-Aleutian” refers to a broader time-zone family, but only the Alaska portion switches into HDT.
The standard-time counterpart of HDT is HST, Hawaii-Aleutian Standard Time, which runs at UTC−10:00. When daylight saving time begins in the Aleutian region, clocks move forward by one hour from HST to HDT, so a local time like 8:00 AM HST becomes 9:00 AM HDT. This seasonal shift changes overlap windows with Honolulu, Anchorage, Seattle, and Tokyo, which can affect cargo timing, weather briefings, and remote communications.
Several other abbreviations share the same UTC−09:00 offset at various times or in different regions: AKST, GAMT, and V. Even though these abbreviations can match HDT numerically, they are not interchangeable in all contexts because each refers to a different geographic or military time designation, so it is important to confirm both the abbreviation and the location when scheduling.
HDT and Daylight Saving Time
HDT exists only during the daylight saving portion of the year in Alaska’s western Aleutian Islands. The zone switches from HST (UTC−10:00) to HDT (UTC−09:00) in spring, then returns from HDT back to HST in autumn. This means local clocks move forward 1 hour at the start of daylight saving time and back 1 hour at the end.
For 2026, the Aleutian region observing this rule changes to HDT on Sunday, March 8, 2026, at 2:00 AM local time, when clocks advance to 3:00 AM. It changes back to HST on Sunday, November 1, 2026, at 2:00 AM local daylight time, when clocks fall back to 1:00 AM. These are the same transition pattern dates used across most U.S. daylight saving jurisdictions, but they do not apply to Hawaii, which stays on HST all year.
This seasonal change has practical scheduling consequences. During HDT, the Aleutian region is 2 hours behind U.S. Pacific Daylight Time, so 9:00 AM HDT equals 11:00 AM PDT; after the return to HST, the gap with Pacific Standard Time remains 2 hours, but the relationship to places on year-round standard time, such as Honolulu, changes because Adak becomes 1 hour ahead of Hawaii during HDT and equal to Hawaii during HST. If you are booking flights, coordinating Coast Guard or fisheries operations, or setting recurring calls, checking the date is essential because the same local clock time can map differently before and after the March and November transitions.
Frequently Asked Questions
What does HDT stand for?
HDT stands for Hawaii-Aleutian Daylight Time. It is the daylight saving version of the Hawaii-Aleutian time zone and uses the exact offset UTC−09:00, meaning it is 9 hours behind UTC during the part of the year when daylight saving time is observed in the relevant Aleutian region.
Is HDT the same as HST?
No, HDT and HST are not the same. HDT is UTC−09:00, while HST is UTC−10:00, so HDT is 1 hour ahead of HST. HST is the standard-time version of the zone, and Hawaii stays on HST year-round, while parts of Alaska’s Aleutian Islands shift to HDT seasonally.
Which cities use HDT?
The best-known populated place associated with HDT is Adak, Alaska, in the Aleutian Islands west of 169°30′ W longitude. There are no principal cities in Hawaii that use HDT, because Hawaii does not observe daylight saving time. In everyday use, HDT is tied to the western Aleutian part of Alaska rather than to major mainland urban centers.
What is the UTC offset for HDT?
The UTC offset for HDT is UTC−09:00. This means when it is 12:00 PM (noon) UTC, it is 3:00 AM HDT. Compared with nearby U.S. zones in summer, HDT is 1 hour behind AKDT, 2 hours behind PDT, and 1 hour ahead of HST.
When does HDT change to HST?
HDT changes back to HST at the end of daylight saving time in autumn. In 2026, that happens on Sunday, November 1, 2026, at 2:00 AM local daylight time, when clocks move back one hour to 1:00 AM HST. This is important for overnight operations, travel itineraries, and recurring meetings because the hour from 1:00 AM to 2:00 AM occurs twice on that date.
When does HST change to HDT?
The switch from HST to HDT happens in spring when daylight saving time begins in the Aleutian region. In 2026, the change occurs on Sunday, March 8, 2026, at 2:00 AM, when clocks move forward to 3:00 AM. Any meeting or transport schedule between 2:00 AM and 2:59 AM on that date is skipped locally because that hour does not occur.
Is HDT used in Hawaii?
No, HDT is not used in Hawaii. Hawaii remains on Hawaii-Aleutian Standard Time (HST, UTC−10:00) throughout the entire year and does not observe daylight saving time. The “Hawaii-Aleutian” name can be confusing, but the daylight-saving form applies only to the Aleutian part of Alaska that follows the U.S. DST schedule.
What is the difference between HDT and AKST?
HDT and AKST can both be written with the same numeric offset of UTC−09:00, but they refer to different zone labels and seasonal contexts. AKST is Alaska Standard Time, typically used for most of Alaska in winter, while HDT is the daylight-saving time used in the western Aleutian area. If you are scheduling across Alaska, using the city name along with the abbreviation helps avoid confusion.
How far is HDT behind UTC and major U.S. time zones?
HDT is 9 hours behind UTC. It is typically 1 hour behind AKDT, 2 hours behind PDT, 3 hours behind MDT, 4 hours behind CDT, and 5 hours behind EDT during the U.S. daylight saving season. For a concrete example, when it is 9:00 AM HDT, it is 11:00 AM in Los Angeles, 12:00 PM in Denver, 1:00 PM in Chicago, and 2:00 PM in New York.