Convert GMT (Greenwich Mean Time) to HST (Hawaii Standard Time)

Best time to schedule a meeting

Standard 9–5 working hours do not overlap at all between GMT and HST. Someone has to take an early or late call — or use asynchronous communication instead.

GMT to HST conversion table

About GMT

Greenwich Mean Time (GMT) is UTC+0. It is used in the UK and Ireland in winter, Portugal, Iceland and much of West Africa.

The trap with GMT is that the United Kingdom is not on it for most of the year. From late March to late October the UK runs BST, UTC+1, so a meeting agreed "10am GMT" with a London colleague in July is an hour out unless both parties meant the abbreviation literally. Broadcasters and airlines avoid the ambiguity by saying UTC. GMT itself is fixed at UTC+0 and does not shift; it is the UK's clocks that move away from it and back.

About HST

Hawaii Standard Time (HST) is UTC−10. It is used in Hawaii, which does not observe daylight saving at all.

Hawaii–Aleutian Standard Time is UTC−10 and Hawaii does not observe daylight saving. That makes it the North American zone whose relationship to everywhere else changes twice a year without it doing anything: Hawaii is two hours behind Los Angeles in winter and three in summer. It is also far enough west that the working day barely overlaps with the US east coast at all.

Does this gap change with the seasons?

This gap is seasonal. The abbreviations themselves are fixed offsets, but the region on GMT switches to BST (UTC+1) from late March to late October. So the 10-hour figure on this page is correct for the part of the year when both places are actually on these abbreviations, and changes by an hour outside it.

HST does not shift, so the whole change comes from one side. A recurring meeting fixed in HST will appear to move by an hour for everyone on the other side, twice a year, without anyone changing anything.

This is the reason scheduling systems store an IANA zone such as Region/City rather than an offset or an abbreviation: the zone knows its own rules and the offset does not.

Frequently asked questions