Puerto Rico, Guam, American Samoa, and the other US territories are often left out of "how time zones work in the US" explanations entirely — but they're officially part of the same federal time zone system as the 50 states, and none of them observe Daylight Saving Time.
The territories and their time zones
- Puerto Rico and the US Virgin Islands use Atlantic Time (UTC-4) — no DST, year-round.
- American Samoa uses Samoa Time (UTC-11) — no DST, year-round.
- Guam and the Northern Mariana Islands use Chamorro Time (UTC+10) — no DST, year-round. Notably, this puts them on the other side of the International Date Line from the mainland US, ahead of UTC rather than behind it.
That's five populated territories, spanning three distinct time zones — none of which change their clocks twice a year, unlike most of the 50 states.
Why none of them observe DST
The pattern lines up with the same logic that keeps Hawaii off DST: Puerto Rico, the Virgin Islands, Guam, the Northern Mariana Islands, and American Samoa are all close enough to the tropics that day length barely shifts across the year. Shifting the clock forward an hour in summer only makes sense where there's a meaningful seasonal swing in daylight to redistribute — near the equator, there isn't one worth bothering with.
Guam: "where America's day begins"
Guam's position is worth calling out specifically, since it's the most counterintuitive one. Sitting at UTC+10, Guam is far enough east across the date line that it experiences each new calendar date before anywhere else under US jurisdiction — genuinely earlier than the mainland, not later, despite feeling geographically "far west" on a flat map. Guam's tourism board has used "where America's day begins" as a slogan for exactly this reason.
The flip side is American Samoa, at UTC-11 — one of the last places on Earth to reach any given calendar date. At certain times of day, it's entirely possible for Guam and American Samoa to be on different calendar dates simultaneously, despite both being US territories.
What this means for scheduling
If you're coordinating with contacts in Puerto Rico, Guam, or American Samoa, two things matter more than they would for a call within the mainland:
- None of these territories shift with the mainland's Daylight Saving Time changes — which produces a genuinely counterintuitive result for Puerto Rico specifically. Since Atlantic Time (UTC-4) never changes, Puerto Rico is one hour ahead of New York during the winter (when New York is on Eastern Standard Time, UTC-5), but the exact same time as New York for the rest of the year (once New York springs forward to Eastern Daylight Time, also UTC-4). The relationship isn't fixed — it depends entirely on which side of the mainland's clock change you're checking from.
- Guam and the Northern Marianas are far enough west (numerically "east" of UTC) that they're often closer in calendar date to Asia-Pacific business hours than to the US mainland's.
The time zone converter handles all of this automatically by location, including the territories that most general time zone guides leave out.
Frequently asked questions
Do any US territories observe Daylight Saving Time?
No. None of the five populated territories changes its clocks. Puerto Rico and the US Virgin Islands stay on Atlantic Time year-round, American Samoa stays on Samoa Time, and Guam and the Northern Mariana Islands stay on Chamorro Time. All of them sit on standard time all year.
What time zone is Puerto Rico in, and does it change?
Puerto Rico is on Atlantic Time, UTC−4, all year with no Daylight Saving. That means it runs an hour ahead of New York during the winter, then matches New York exactly for the rest of the year once New York springs forward — the gap opens and closes without Puerto Rico touching its clocks.
Why don't the territories change their clocks?
Partly law and partly latitude. The territories were never brought under the federal DST mandate that the Uniform Time Act of 1966 applies to the states, and most of them sit close enough to the tropics that the seasonal swing in daylight is small enough not to be worth redistributing.
Why is Guam called “where America's day begins”?
Because Guam sits west of the International Date Line at UTC+10, putting it a calendar day ahead of the mainland, so it reaches each new date before anywhere else under US jurisdiction. In practice it also means Guam's working hours line up with Asia-Pacific business hours rather than the mainland's.