Time zone · Americas
HDT
Hawaii-Aleutian Daylight Time
Hawaii-Aleutian Daylight Time (HDT) shifts the remote Aleutian Islands an hour out of step with Hawaii, meaning your workday starts already mid-morning for much of North America while the rest of the U.S. is just waking up.
Saturday, May 30, 2026
Current offset
UTC-09:00
Daylight · HDT
Daylight saving
Active
Reverts 1 Nov 2026
IANA zones
1
1 observe DST, 0 don't
DST offset
—
No summer variant
About HDT
Standard time, with a summer shift.
Hawaii-Aleutian Daylight Time (HDT) shifts the remote Aleutian Islands an hour out of step with Hawaii, meaning your workday starts already mid-morning for much of North America while the rest of the U.S. is just waking up.
IANA zones · the technical identifiers
The zone that resolve to HDT.
For software, always store the IANA identifier — never the abbreviation alone. The database keeps these zones distinct because their rules can, and historically did, diverge.
Where HDT is used
One country.
Same offset · UTC-09:00
Other zones at UTC-09:00 right now.
These named zones share HDT's offset today. When daylight saving rules differ, they drift apart for part of the year.
Frequently asked questions
Common questions about HDT, daylight saving, and how to handle it in software. Can't find what you need? Email [email protected].
- How is HDT different from standard Hawaii time?
- Hawaii stays on UTC−10 year-round, but the Aleutian part of this zone an hour closer to the International Date Line springs forward to UTC−9 during daylight time, splitting the two far-flung U.S. island communities save for a few months each year.
- Where in the U.S. actually uses HDT?
- Practically only the western Aleutian Islands around Adak, Alaska, observe HDT—making it the America/Adak time reference and one of the smallest-populated U.S. time communities.
- Why only one time zone?
- The Aleutians stretch so far west that aligning them with Alaska’s other mainland zones would put churches and schools waking in winter around 3 a.m. in darkness; anchoring them a day-ahead from Honolulu keeps civil time closely tied to solar noon.
- Do other Alaskan zones follow HDT too?
- No—Anchorage and the rest of Alaska sit a full hour ahead on Alaska Daylight Time during the summer, so the Aleutians effectively start the workday nearly simultaneously with places near the Ural Mountains.
- What’s unique about the Aleutians’ geography?
- Crossing into Adak means stepping near the edge of the western hemisphere; Adak is actually further west than Hawaii, yet keeps a date-based political tie to the United States and swings its clocks so society doesn’t freeze while the sun never sets.
- Is HDT observed year-round anywhere?
- No—the Aleutians revert to Hawaii-Aleutian Standard Time (UTC−10) every November, so HDT exists for roughly the same March-to-November span much of the mainland U.S. experiences.
- How old is this time arrangement?
- The Aleutians inherited the Hawaii half of their label after World War II reorganizations, carrying forward a daylight-saving tweak that has kept daylight roughly civil-helpful for the islands since then.
- What’s fun about Adak specifically?
- Adak recently made news in distance-running and weather-watching circles; scheduling a zoom call at noon HDT aligns with Parisians’ morning commute, neatly disguising Adak as a European ghost-town.
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