Daylight Saving Time is a huge mess

Daylight Saving Time (DST) is a huge mess. For example, what is the time difference between Paris and Houston? It’s seven hours today. Yesterday it was six. A couple weeks ago it was seven.

Countries observe DST at different times or not at all. Even within one country it can be complicated. For example, the US generally observes DST. But Arizona, Puerto Rico, Hawaii, U.S. Virgin Islands, and American Samoa do not. And even within Arizona, the Navajo Nation does observe DST.

I wish everyone would take a few minutes to learn about universal time, UTC. It is essentially the time in Greenwich, England except it ignores DST. Learn how your time relates to UTC and use UTC when communicating with people who don’t share your time system. This allows, for example, a group to announce the time of a conference call in UTC and let everyone convert that to their local time. This is so much simpler than “your time”, “her time”, “his time” etc.

It’s also convenient to let people know how your time zone relates to UTC. For example, Houston time is UTC-6, i.e. six hours behind UTC. When someone asks in an email what my time zone is, maybe so they could call me during normal business hours, I may say Central Time, UTC-6. (Or in the summer, UTC-5.)

[The abbreviation UTC is an odd compromise. The French wanted to use the abbreviation TUC (temps universel coordonné) and the English wanted to use CUT (coordinated universal time). The compromise was UTC, which doesn’t actually abbreviate anything.]

Update: I’m not suggesting that people set their watches to UTC. Time zones are necessary. And if part of the world wants to have DST and another part doesn’t, vive la différence. I’m only suggesting that people use UTC when communicating with others outside their time zone.

Related post: Software engineering and alarm clocks

76 thoughts on “Daylight Saving Time is a huge mess

  1. UTC! I’ve always wondered what to do with the “second time zone” setting on my wristwatch. Now it’s UTC. Thanks for the tip.

    AB: Since there are no rules for abbreviations (Mrs, BBQ, PA, etc), we’ll just muddle along with UTC.

  2. Agree – and in my experience it creates a lot of extra work for IT staff all over the world, for no real gain. Many software products require updating to later releases to get fixes to time zone databases. These out-of-band updates are very unwelcome to IT staff, because of the need for testing each release in staging areas, and is made worse by cascading dependencies between product versions. Truly an unnessary mess.

  3. You are right!

    I will say about Russia.

    Several months ago our president cancelled DST in Russia, because incoviniences due to time changing were higher than energy savings. Nevertherless, two weeks ago computers and mobile phones adjusted clocks one hour ahead. This was predictable, so we manually adjusted clocks back.

    But what was wery strange is that one week ago some computers and mobile phones adjusted time one hour back without warning! In result, we was late to a doctor.

    Only people with simple wall clocks were able to go through this revolt of the machines!

    P.S. You should also mention leap seconds. They are not known ahead in time, so we can not precisely calculate time difference between dates in future.

  4. Corrections to my comment: computers in Russia adjusted time one hour back at October 31st, as usual (inspite of DSC cancellation), then at November 4th, Microsoft updated timezone tables for Russia, and, surprisingly, time was adjusted again 1 hour back.

  5. @Anton

    Russia did not cancel DST. Instead they (you) just never returned to “normal” time.

  6. [The abbreviation UTC is an odd compromise. The French wanted to use the abbreviation TUC (temps universel coordonné) and the English wanted to use CUT (coordinated universal time). The compromise was UTC, which doesn’t actually abbreviate anything.]

    Is this right? I thought the odd letter order was to maintain continuity with UT0, UT1, etc. [].

  7. Is this different from GMT? And if so, is that designation no longer in common use? Alas for the legacy of the Astronomer Royal…

  8. Seattleite: GMT and UTC are essentially the same thing. There are subtle differences that most people can safely ignore.

  9. > Russia did not cancel DST. Instead they (you) just never returned to “normal” time.

    In Putin’s Russia, time changes you!

  10. One should note that Unix machines always keep their hardware running on UTC and then adjust from there if necessary; this is why you don’t have to worry about adjusting the clock on a Unix, you just adjust the time zone files if there is a problem. In my experience Unix tzdata files are usually updated within hours of a public announcement about changes in time zones.

  11. How is using UTC offsets any different from just saying Central Time? You still have to take DST into consideration – “Central Time, UTC-6. (Or in the summer, UTC-5.)”.

    How does saying UTC-6/5 depending on DST offset make it easier? To me it looks like this just adds more math to the equation, while earlier you just had to figure out what Central time is now.

  12. Ram: The difference is that I’m responsible for keeping up with my own time zone’s peculiarities. I tell people I’m UTC-6 when I am, and UTC-5 when I am. I don’t expect Europeans, for example, to keep track of when the US changes its clocks. And if they do the same, I don’t have to keep track of their time changes either.

  13. @rfk «In Putin’s Russia, time changes you!»

    No, this was our president Medvedev who cancelled time change in Russia. Medvedev is famous by many small changes he made (like reforming militia to police, moving some goverment services to the Internet and so on). These reforms look funny given that the country is in trouble, and time changing is not the thing he should worry about.

  14. [with corrected links]

    Nice post!

    A very practical solution I’ve found is to use the Event Time Announcer provided by

    As an event organizer, it allows you to convey clear schedule information to the participants. Here is an example. For an event on Saturday, 12 November 2011, 12:00 New York time, it produces the following table giving the corresponding time in different places. It then becomes a simple look-up task for the participants.

  15. I was recently in a bar and I saw a countdown clock to the number of minutes until the next hockey game. I commented to my drinking partner that I would never have the guts to create such a device. Due to crossing several DST changes the risks of a sign error bug would be just too high for a device that I could not patch later.

    So for me DST changed something as simple as a timer into an engineering marvel.

  16. Describing “what my time zone is” is a lot of work if you’re talking about an event that recurs: you need to describe the rules for when you change UTC offsets, and what offsets you have before and after the changes. Ideally, we could just exchange time + location, and software could use the Olson tz database plus the map data at to figure out what time was intended.

  17. Re your edit: Are timezones necessary? If I go to work at 10pm and come home at 6am, and that’s dawn to dusk, who cares? Let’s just do all UTC, always.

  18. And the most important question of all: why do people in Greenwich get to be in charge? Didn’t the British Empire collapse a very long time ago?

  19. I’m reminded of Swatch time.

    First, it’s decimal time in “beats”, not seconds and minutes. That’s the part I least liked. The part I kinda liked is how there was one planetary time. If the time is 358 in Bern, it’s 358 in Delhi, Perth, Vegas, wherever. Then there’d be a local convention as to when start-of-business, lunchtime, etc., were.

    I mention Bern because, as “Swatch” comes from “Swiss Watch”, it was centered on Bern time.

    It strikes me that Pacific islanders getting up one day and going to bed the next day would be weird, but a regular daily bout of cognitive dissonance fits in the mind better than one that occurs twice a year on a freely-moving date.

  20. I used to have a Timex Iron Man watch with two time zones, and when I would travel, I would move to the one I had set to UTC and remember the offset, so I could always press a button and know what time it is at home.

  21. I’m surprised no one’s mentioned the fractional hours present in some time zones. That’s got to be even worse to keep track of from a human, and potentially software, standpoint. The culprits (current, I think):

    Maquesas Islands, French Polynesia — UTC -09:30
    Venezuela — UTC -4:30
    Newfoundland (and sotuheastern Labrador), Canada — UTC -3:30 / -2:30
    Iran — UTC +3:30 / +4:30
    Afghanistan — UTC +4:30
    India — UTC +5:30
    Sri Lanka — UTC +5:30
    Nepal — UTC +5:45 (!)
    Cocos (Keeling) Islands, Australia — UTC +06:30
    Myanmar — UTC +06:30
    Northern Territory, Australia — UTC +09:30
    Lord Howe Island, Australia — UTC +10:30 / +11:00 (!!!)
    Broken Hill, New South Wales, Australia — UTC +10:30
    South Australia, Australia — UTC +10:30 / +09:30
    Norfolk Island, Australia — UTC +11:30
    Chatham Islands, New Zealand — UTC +12:45/ +13:45 (!)

    I seem to recall in the not-so-distant past that Newfoundland was the only place with a time zone with an offset which was not in whole hours.

    I was delighted to find a wristwatch for $57 which sets the time based on radio signals, and it always handles DST in the Central time zone in the US perfectly.

  22. Oh yeah — and in the US, in Indiana, the decision of whether to follow daylight saving time or not was until recently left up to local government. Fun fun fun as you change your watch driving around Indiana, I’d imagine.

    A good friend who grew up there swears that the reason it was left up to local government choice was the outcry from farmers who insisted their crops couldn’t take an extra hour of daylight in the summers. Of course, I suspect he never let facts get in the way of a good story.

    On the other hand, the actual history is truly a tale of legislative magnificence:

  23. I live in Indiana. Used to have long discussions with support in Chicago over when to schedule upgrades, but beyond that, there wasn’t normally a problem. Counties near Chicago moved their time with Chicago. Counties near Cincinnati moved their time with Cincinnati, and the rest of the state didn’t, until Mitch Daniels moved us to follow the rest of the nation in folly. I don’t think it ever really affected me that much.

  24. I wasn’t thinking that the time zone affiliation would be a problem as much as the selective observance of daylight saving time. That probably wasn’t as problematic as it sounds, but I could imagine two adjacent counties with the same time in winter but differing by an hour in summer. Probably it is not realisitc but I also imagined driving across Indiana in summer and having the local time change everytime a county line was crossed.

    Dave, do you happen to live in Anderson? My buddy grew up there, and has a *bunch* of colorful tales to tell.

  25. I believe China has one time zone for the whole country! This makes sense in some ways I guess.

  26. If daylight savings time is the next best thing to sliced bread, then why doesnt UTC and/or Greenwich Mean time move their time also (kidding of course, what a nightmare that would be). However, if the UTC reference changed, then wouldn’t everyone else have to do nothing? Side note: Our dog is used to be fed dinner at 6:00PM. Try to tell a hungry dog that its REALLY only 5:00PM. She peed on the kitchen floor as she is used to be let out at 6:00AM. Her bladder didn’t know to hold it one hour longer for the REAL 6:00AM. Thanks Mitch Daniels.

  27. I work for an American company and all of their meetings are scheduled in EDT / EST. This is very frustrating as I live in GMT / BST. I cannot persuade them to used GMT-x / GMT-x as everyone ought to know their GMT offset. Having said that, I can never remember whether BST (British Summer Time) = GMT+1 or GMT-1.

    To complicate things further, the UK government is looking at using BST all year round or introducing double daylight saving time. What is wrong with just using your local time zone (e.g. GMT in my case) and working 8 a.m. to 5 p.m. some months and 9 a.m. to 6 p.m. other months? Much simpler than changing dozens of timepieces.

  28. You almost made it. You were doing fine until you wrote “in the summer”. As someone who routinely works with folks in Australia where the time difference varies between 14 and 16 hours from Cambridge (MA) you must learn to say “in my summer”.

    There isn’t a “the” summer in that situation.

  29. :-)

    Ultimate Triangle Clocks
    Ultimate Ticking Clocks
    Universally Turning Cogs

    I am on GMT Get Less Time, what i really want is Get More Time

  30. @Geoff – Yes, perfect. Of course, I live in England…

    @Ram – I’m struggling to comprehend quite such parochial thinking. How many places have a “Central Time”? And how exactly do I find out what your version of Central Time is just now?

    @John Venier – I used to live in South Australia. I recall back in the early 90s using several pieces of software (which exactly escape me for the moment) that did not acknowledge the existence of fractional timezones at all.

  31. Couldn’t agree more! Hospital charting systems are a real PITA at DST boundaries… imagine charting fall back; is it 1am 2am 2am 3am… hmm… Or 1am 2am 3am with 2am actually spanning 2 physical hours…. how many hours in the day are there at the spring forward boundary? 1am 3am 4am My brain hurts just thinking about it.

  32. I actually love DST, although there are some bad implementation details like inconsistencies within the US and between the US and Europe. It is a lot easier to change clocks, especially these days with the Olson database, than to convince most businesses, schools and other institutions to change their schedules. Maybe your employer is enlightened enough to change an 8-4 schedule to 9-5 during the summer. But what if your child’s school doesn’t do the same? Or decided only to move things 30 minutes, or to phase the change in over a 2 month period? Or starts the unofficial DST a few weeks before or after? It would create an (even bigger) mess.

    DST solves a big coordination problem. Almost everyone does manage to change their schedules at the same time, within a country and we all benefit. If there is a minority, such as farmers, for whom DST is inconvenient, then the cost for them of changing their schedules is much lower than it would be for everyone else to do it, even if we didn’t have to mess with clocks.

  33. Most international companies have been using UTC for a couple of decades. It’s domineering US companies or US companies without international operations that impose local time.

  34. In Greenwich it is GMT (Greenwich Mean Time) in winter, but BST (British Summer Time) (GMT+1:00) in the summer.
    Some UK politicians want us to switch to DST (Double summer time or GMT+2:00) in the summer and BST (GMT+1:00) in the winter.
    So Greenwich will no longer use GMT or as some people call it UTC.
    The only reason for this is to make us (The UK) more like the rest of Europe.
    In reality it means we will go to work in the dark, have more road accidents (Children walking to school in the dark) and trying to go to sleep when it’s still light.

  35. Don’t forget the mess it causes with computers. Some OSs do a better job than others keeping up with DST changes. If you have legacy UNIX systems it can really be a pain.

  36. The reason the British get to name time (GMT) is because we invented the first co-ordinated time and navigation system based in Greenwich London.
    You cannot navigate a ship on maps alone, you need to know what time it is as well, and this has to be the same for everyone, hence the establishment of the standard time at greenwich to which all ships clocks were set and is on longditude 0.
    Being first is always important!

  37. Not to mention trying to deal with financial market data. EST is the time most US markets are marked in. But then DST shows up and now you have to shift your market data times around if you’re not in the EST timezone or not on DST for the US. And if you’re dealing with UK markets, or AUS markets…, what time did the market open? Hell, I don’t know, last hour, next hour. Bah! Get rid of all timezones and just have a single time for the entire planet. We just do stuff at different times from longitude to longitude. I get up at 15:00 UTC and go to sleep at 6:00 UTC. Brits get up at 7:00 and got to bed at 22:00. There, done, no more nonsense.

Comments are closed.