Hooray for Eastern Standard Time!

Well, I'm back from vacation and thanks to this morning's time change (at least in the US), very glad to be back into Eastern Standard Time! Warning: Timezone misunderstandings are a huge pet peeve of mine. Ask my friends. :) 

This is the easy part of the year -- the half of the year where no matter how little someone understands timezones, they can blithely state that the meeting is at "2pm EST" or that they work "8-5 EST" and actually be right! During Daylight Saving Time (essentially, April -> October in the US), lots of people I interact with still refer to Eastern Standard Time, totally oblivious to the fact that they are referencing a different timezone than they're currently in.

So, here's the short version -- a pocket guide, if you will:

  • Greenwich Mean Time (GMT/UTC) is a fixed timezone. It never changes.
  • Eastern Standard Time (EST) is also a fixed timezone. It is (always) GMT-5:00.
  • Eastern Daylight Time (EDT) is also a fixed timezone. It is (always) GMT-4:00.

In (most of) the US, we simply jump back and forth an hour twice each year -- we switch into a different timezone. EST is always 5 hours behind GMT. EDT is always 4 hours behind GMT.

And here's the important thing: If you say the meeting is at 2pm EST... during July.... in Charlotte, NC... do you mean that we should show up at 3pm EDT? Should I just assume you don't understand timezones when I put the meeting into my Outlook calendar with a 2pm EDT start time? Computers understand timezones, of course!

See these links for additional information:

https://wwp.greenwichmeantime.com/time-zone/rules/usa.htm

https://wwp.greenwichmeantime.com/info/daylightsaving.htm

https://www.boulder.nist.gov/timefreq/general/misc.htm#Anchor-32566

https://webexhibits.org/daylightsaving/

(this post dedicated to Michael, Scott and Jodi - who get to listen to me rant on this topic at least twice each year). :)

Updated Jan 17, 2005 – I’ve written a utility that’ll tell you how your machine’s timezone settings are configured. This won’t tell you which timezone you’re in (that’d be a neat trick!), but it’ll tell you which timezone your machine is currently configured for plus all the DST stuff. Get it here.