What is the common practice with regards to differentiating between UTC and GMT?

Question

I finally found out the difference between UTC and GMT by making the effort to look it up on Wikipedia today. Technically speaking it appears that GMT != UTC because you do not know if it is UTC or UT1 being referred to. However practically, people use the terms interchangeably to indicate the same timezone.

A while ago, I suggested that we change the user interface of one of my companies apps to display UTC instead of GMT.

Just to be sure that our database was not calculating the potential seconds difference between GMT and UTC, I ran the below query and verified that they both are just acting as aliases for the same timezone.

select now() AT TIME ZONE 'GMT', now() AT TIME ZONE 'UTC';
          timezone          |          timezone          
----------------------------+----------------------------
 2009-02-11 08:46:11.643032 | 2009-02-11 08:46:11.643032
(1 row)

What do you think? Do enough users out there understand UTC? Is it better to use the older but more common term? Or should I just do a UTC/GMT?

Answer 1

Normal humans don't need to worry about the few seconds difference between GMT and UTC. The difference only matters to astronomers and time nerds.

I have seen very little software that bothers to make the distinction. Most software ends up using the labels "GMT" and "UTC" interchangeably. Typically it just means "clock time after removing the local time zone offset in exact hours (or half/quarter hours)."

Answer 2

Personally, I think of the term UTC before I think of GMT.

Answer 3

I think of GMT before UTC, but I am also living at GMT (+/-0)

Answer 4

In most cases, nobody will be concerned about the sub-second technical difference between GMT and UTC.

However, writing that the time is expressed in UTC instead of GMT avoids one source of confusion: Greenwich (and the UK in general) is currently GMT+01:00 because of the daylight saving time (DST).

GMT+01:00 does not mean 1 hour ahead of the time in the UK as one could mistakenly think. Because of the DST, GMT+01:00 is currently the exact time in England. Stating it as UTC+01:00 helps to avoid this confusion.