The Short Answer
Hawaii is in the Hawaii-Aleutian Standard Time (HST) zone, which is UTC-10. That's it. No daylight saving time, no exceptions on the main islands. If you're calling someone in Honolulu from New York in the summer, it's a 12-hour difference. In the winter, it's still 12 hours because nobody in Hawaii changes their clock. The zone itself covers more ground than most people realize. It runs from the westernmost tip of Alaska's Aleutian Islands clear across the Pacific to Hawaii. The Aleutians that fall west of 169°30′W observe Alaska Time with daylight saving, while everything else in the zone stays on HST year-round. I learned this the hard way when I was coordinating a live stream between a producer in Anchorage and a crew in Hilo. The Anchorage team had just flipped to AKDT, so they thought the call time was 7 PM HST. It wasn't. It was 6 PM HST. We missed the first thirty seconds of the segment. Here's the thing nobody emphasizes enough: Hawaii does not observe daylight saving time, and that single fact causes more scheduling errors than any other quirk in the zone. When the rest of the US swings to EDT or PDT, the gap between Hawaii and the mainland shifts. New York goes from 3 hours behind to 4 hours behind. Los Angeles goes from 2 hours behind to 3. If you're building a booking system or a broadcast schedule and you hardcode a fixed offset from Pacific Time, you will be wrong half the year.
I worked on a project once where we built a recurring event system for a chain of coffee shops with locations in Honolulu, Los Angeles, and Chicago. The backend stored everything in UTC and used simple integer offsets. For six months it worked fine. Then October hit, California switched to PST, and suddenly the Honolulu launch times were drifting an hour later each week relative to the LA team's calendar. We had to patch the system to explicitly reference the IANA tz database entry for Pacific/Honolulu instead of treating HST as a static UTC-10 value. The IANA entry is still UTC-10, but the reason we switched wasn't about the current offset — it was about making sure the code would never accidentally try to apply DST rules to Hawaii. A lot of libraries default to "apply DST if the region is in a DST-observing zone," and Hawaii trips that logic up because the zone name contains "Aleutian," which does observe DST.
How the Offset Works in Practice
UTC-10 means when it's noon in Greenwich, it's 2 AM the same day in Honolulu. When it's 9 AM in Los Angeles during standard time, it's 7 AM in Hawaii. During California daylight saving, that becomes 8 AM Hawaii time for a 9 AM LA time. The math is straightforward but the transitions are easy to mess up if you're doing it mentally under pressure. The Aleutian Islands split is another detail that matters if you're dealing with anything spanning Alaska and Hawaii. The islands west of 169°30′W — Attu and some of the Near Islands — actually sit in the HST zone geographically but observe Alaska Time with DST. So Attu is UTC-9 standard and UTC-8 during DST, while Honolulu is always UTC-10. That means for roughly seven months of the year, Attu and Honolulu are only one hour apart instead of two. I've seen flight schedules get confused by this. Airlines sometimes list the Attu-Honolulu route with a one-hour difference in summer and a two-hour difference in winter without making it obvious in the booking interface.
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Edge Cases That Will Bite You
Here's a specific scenario I ran into: scheduling a weekly standup between Honolulu and Tokyo. Tokyo is UTC+9, Hawaii is UTC-10, so the difference is 19 hours. A 9 AM Monday standup in Honolulu is 4 PM Tuesday in Tokyo. Easy enough. But when the US starts observing DST in March, people in other time zones assume Hawaii shifts too. They schedule the call for 9 AM Hawaii time, meaning 2 PM Tokyo time, and show up at 4 PM Tokyo time expecting it to be "Hawaii morning." I had to put a running note in the calendar invite for two years straight: "Hawaii does not change clocks. This time stays the same year-round." Another one that comes up constantly: date line crossings for multi-island operations. Hawaii is on the eastern side of the international date line, but the Aleutian Islands stretch west of it. If you're managing logistics across both, you'll occasionally have a situation where your "same day" shipment departs from Honolulu and arrives in Attu on what the Attu crew records as the next calendar day, even though only a few hours have passed. It's a timezone artifact, not a real time difference, but it breaks inventory systems that assume geographic proximity means calendar synchronicity.
What This Means for Scheduling and Software
If you're building anything that touches Hawaii time, use the IANA identifier Pacific/Honolulu. Do not use a fixed UTC-10 offset in your database unless you've explicitly documented that it will never need to account for historical changes. Hawaii has been on UTC-10 since 1947, so the risk is low, but the zone name still carries DST rules for the Aleutian portion, and mixing them up in code is a real problem. For manual scheduling, the easiest mental model is: Hawaii is always 10 hours behind UTC, and it's always 2 hours behind Pacific Time regardless of the season. That second rule is the one people forget. Pacific Time flips between UTC-8 and UTC-7, but Hawaii stays locked, so the delta between them flips too. If you need a reference tool, most operating systems handle this correctly out of the box now. Windows, macOS, and Linux all pull from the same IANA database. The issue almost never comes from the OS — it comes from application code that makes assumptions about what a time zone name implies. A well-configured calendar app will show the correct times automatically. A custom-built scheduling tool is where you'll find the bugs.
