Guam and the Northern Mariana Islands: The US Time Zone Furthest Ahead

Guam and the Northern Mariana Islands use Chamorro Standard Time, fixed at UTC+10 year-round with no daylight saving. This makes it the only US time zone with a positive UTC offset — every other US zone is behind UTC, not ahead of it.

Guam runs roughly 14 to 15 hours ahead of the US East Coast and about 17 to 18 hours ahead of the US West Coast, with the exact gap depending on whether the mainland is currently on standard or daylight time. In practical terms, this typically means Guam is already well into the next calendar day while the mainland is still finishing the day before.

For anyone scheduling a call between Guam and the mainland, it's often easier to think in terms of 'tomorrow morning in Guam is tonight on the mainland' than to track the exact hour difference, since the date change accounts for most of the practical confusion.

Guam and the Northern Mariana Islands sit near the equator, where day length barely changes across the year, making daylight saving unnecessary for the same reason it's skipped in Hawaii and Puerto Rico.

Because Chamorro Time is so far removed from every other US zone, Guam and the Northern Mariana Islands rarely factor into mainland-focused scheduling tools at all, and are usually treated as a special case requiring an explicit, separate time check rather than folded into a broader nationwide calculation.

Guam's position just west of the International Date Line also gives it a symbolic distinction: as US territory, it's among the first places in the world, and the first point on US soil, to begin each new calendar day — a fact often noted in coverage of New Year's celebrations, since Guam rings in the new year many hours before the mainland.

Guam and the Northern Mariana Islands also fall under the same Uniform Time Act framework that lets Hawaii and Arizona opt out of daylight saving, though in this case the exemption was never seriously in question given how little the islands' day length varies across the year.