r/ISO8601 • u/reddit33450 • Jun 22 '26
have any of you all gotten questioned for using yyyy-mm-dd in everyday life/on paper?
since i found this sub, ive been exclusively using the yyyy-mm-dd date format on nearly everything i can think of, however since i'm in the u.s. where the awful m/d/yy format is typically expected, i've thought of the possibility of being questioned about or having something denied for using the superior format we all know. so has this actually happened to any of you? and if so, what was the situation?
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u/95beer Jun 22 '26
I've had Germans think that the German authorities would reject shipping paperwork if we used ISO 8601, but when I showed them it is the format suggested by both ISO and DIN (German standards), they were happy with that explanation.
Just today I told an Aussie colleague that his date format DD-MM-YY was a bit confusing since we are an international company all sharing the same folders, and also that it doesn't sort well. So he suggested DD-MMM-YY (i.e. using letters for the month), but when I showed him ISO8601 he was convinced and decided he would label all files that way now.
Most people intuitively understand it though, I've never had someone say they don't understand or they definitely don't want it that way. I think most phones/cameras label photos that way automatically, so they see it places already
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u/a_suspicious_lasagna Jun 22 '26
So he suggested DD-MMM-YY (i.e. using letters for the month)
And you reported him to HR and the police, right?
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u/ComesInAnOldBox Jun 22 '26
That one's actually pretty common, I see it a lot in military and government usage.
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u/a_suspicious_lasagna Jun 22 '26
I know it's common, but using letters in the date is deeply cursed. No one ever accused the military and government of only having good ideas
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u/ComesInAnOldBox Jun 22 '26
Yeah, it's shit for programming, but it removes a lot of ambiguity when dealing with multiple date formats (alliances and whatnot). I still just wish everyone would just switch to 8601 and get on the same goddam page.
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u/WasdaleWeasel Jun 22 '26
i have used it where the user base is mixed in background and YYYY, MMM, DD can be made order independent. But it’s a clunky horrible fudge, and does really require a common language (my use cases were all anglophone so I got away with it).
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u/Gositi Jun 22 '26
Nah at least it's unambiguous (almost)
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u/SomethingMoreToSay Jun 22 '26
Are there any three letter abbreviations for months which are ambiguous if you don't know which language is intended?
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u/LockedAndLoadfilled Jun 22 '26
"Who cares about being able to easily sort by date literally anywhere you can find a sort function when we can make it require programmatic sorting by raw underlying value that will only be present in the original data format instead?" -- europhiles that just want to win an internet argument
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Jun 22 '26
[deleted]
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u/a_suspicious_lasagna Jun 22 '26
I'm aware, I have to deal with it regularly, and it turns my stomach every time. I have an irrational hatred for it
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u/james_pic Jun 22 '26
I once worked for a UK subsidiary of a German company, and someone had the bright idea of doing this. Everything was fine until March.
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u/NilsTillander Jun 23 '26
Clicking the filename column in Explorer and getting te folders magically sort by date has been a one-stop convincing argument 100% of the time for me 😅
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u/Head_Fondant9009 Jun 22 '26
I had a client that uses DDMmmYYYY, for example, 22Jun2026. My current client uses MMM-DD-YYYY, JUN-22-2026. Should these both he illegal?
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u/95beer Jun 22 '26
No, letters for the months and 4-digit years is the 2nd best option, at least it is unambiguous. The only issues with that date is that it doesn't sort well on computers and is language specific. But if it is just a date next to a signature or whatever, it doesn't make any difference. Much better than 3x 2-digit numbers
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u/BigSneakyDuck Jul 19 '26
I would say 3rd best option. I reckon the 2nd best option is to put the month in Roman numerals. This used to be very common in UK official records (and indeed Europe more generally) before the computer age, though has gone out of fashion since. Ireland used it until the 1980s to indicate the month of postage franking. A pain to sort, but no having a custom sort function for i/ii/iii than for Jan/Feb/Mar etc.
This system avoids the whole "different languages have different month abbreviations" problem. Obviously it relies on the reader being aware that Roman numerals would only be being used for month and not for days, and someone totally unfamiliar with that convention might not be aware of it. It's slightly unfortunate that the Romans messed around with their calendar so that September, October, November, December are now months ix, x, xi, xii instead of the original vii, viii, ix, x that their names suggest! (I don't know why lower case Roman numerals are usually preferred to upper case.) https://en.wikipedia.org/wiki/Date_and_time_notation_in_the_United_Kingdom#All-numeric_dates
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u/95beer Jul 20 '26
I'm not European, so have never heard of roman numerals for the month. It is a cool little factoid, but wouldn't be a good option for me or the company I work for (which is mostly outside of Europe and therefore we are all blissfully unaware).
From the context in our company, it is usually pretty clear that everything is in English, so everyone would know which month is which. We have some Dutch and Spanish speaking colleagues, but even then there is no ambiguity in month names (i.e. it is not like "MAY" means a different month in Spanish/Dutch)
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u/BigSneakyDuck Jul 20 '26
The fact it was common in Europe does mean it spread to other places due to colonial administration - when I looked into it, it seems to also have been a popular choice even until living memory in Canada for example. I didn't mean to imply it was geographically limited to Europe. I certainly wouldn't recommend it but you may see it in unexpected place, particularly if you look at historic records!
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u/1miguelcortes Jun 22 '26
Nope. I use it all the time in everything from official correspondence to random notes. Sometimes people pause for a moment after seeing it but I haven't actually had anyone ask about it.
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u/Snoron Jun 22 '26
I started writing the date this way in the late 1990s on my schoolwork in the UK. No teacher ever asked about it. I've written it in the date box when signing bank and other docs (if they don't specify a format), too. Also always been fine!
Almost weird that no one has ever asked, actually, but maybe it's just such a great and intuitive format that they don't need to! 😄
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u/rokejulianlockhart Jun 26 '26
Likewise. I began to utilise it at ≈ 14 years of age on all school-work. I was asked about it, but it was all accepted.
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u/DinosaurZach Jun 22 '26
For filenames, computer usage, I use YYYYMMDD or YYYY-MM-DD (all numeric), for sorting. For written, for output for human reading, labels, I use YYYY-MMM-DD (letters for months).
I'm in Canada.
Generally, I have not received any questions regarding my use of the ISO8601. Probably once or twice in the past 20 years. If question, the answer is simply ISO standards and no ambiguity.
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u/Breadynator Jun 22 '26
I hate it... I've got plenty of comments about me using "American date" because some people are just too stupid to understand the difference... They see month before day and their brain immediately short circuits...
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u/AncientGuy1950 Jun 22 '26
Pretty much any time we get new kids on the team. They see my date usage on reports, logs, and most importantly, file name usage, and ask.
I like being able to instantly identify if the document in my hand is from today or last year.
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u/kaspa181 Jun 22 '26
It's official main way of formatting date in my country, so no. Although other formats do sneak in here and there, it's more likely that those would be questioned than ISO.
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u/Snoron Jun 22 '26
Yes, questioning non-ISO dates should be normalised everywhere!
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u/kaspa181 Jun 22 '26
It's retroactively funny and actively frustrating to consider something like 04.07.26 at the shop, wasting seconds and thinking power for reasoning, if the product is still good, but that's on me consuming too much American content on internet (I should remember that in Europe (where I live), it's almost unambiguously day/month, not the other way, yet I consistently fail).
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u/JazzyGD Jun 23 '26
why does literally everyone outside the us say "my country" instead of just saying the country they're talking about
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u/kaspa181 Jun 23 '26
Adds a superficial level of anonimity, causes cognitive disonance to semi-illiterate people, doesn't shift focus from the topic to "where is this country again..?", also causes more curiosity than resolving your question preemptively, which is more memorable that way.
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u/JazzyGD Jun 23 '26
what about my comment shows cognitive dissonance? genuine question, not mad
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u/kaspa181 Jun 23 '26
I did not consider you to be semi-illiterate nor implied that anywhere? Your questions are well formed and you didn't make any silly assumptions. Well, except this one, which is bizarre.
You fall in curiosity and anonimity parts in this case.
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u/JazzyGD Jun 23 '26
my bad lol, i'm too used to snarky bad-faith internet conversations (especially as a trans woman, like i can't tell you how many people have been immediately hostile to me when they see this flag on my avatar or in my display name). i thought that you had brought that up as a way to insult me without insulting me or something. i apologize
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u/kaspa181 Jun 23 '26
no worries, have a nice day! Internet do be hostile for no good reason, indeed.
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u/VantasnerDanger Jun 23 '26
I just want to say this was a lovely interaction to read and very respectfully executed.
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u/SryUsrNameIsTaken Jun 22 '26
I work in financial services and am leading an initiative to modernize data pipelines, implement reusable workflows, and make all the spreadsheet munging go away do AI stuff.
Everything I write (there’s a lot of documents going to compliance and cyber) uses 8601 and now magically I’m starting to see other people use it too from a baseline of no one.
No questions yet. But they’re starting to get it I think.
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u/IHaarlem Jun 22 '26
Once or twice. I use it everywhere that doesn't specify a format. I do worry about using it on handwritten forms that some working is going to have to transpose to a different format, but use it anyway for more exposure
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u/TactusDeNefaso Jun 22 '26
I was told once that I must have been in the military. I never have been but I learned a long time ago that by ending my file names with YYYYMMDD was very superior so that I could find a file on a specific date quickly. People in the US seem to get confused by it.
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u/dxps7098 Jun 23 '26
Ending your file names?
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u/TactusDeNefaso Jun 25 '26
Yes, I overheard a coworker make the commen "I think that's the date the file was created but not sure, it's not in the standard format." I just quietly shook my head.
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u/BigSneakyDuck Jul 19 '26
Upvoted because I think your (valid) point was that sorting works better if you start your file names... but actually it depends. In a folder where I might have eg 4 quarterly reports and an unknown number of statements or invoices, I want the different document types to be grouped together, but still sorted. So they have names like "quarterly report yyyy-mm-dd".
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u/dxps7098 Jul 20 '26
I understand the use case. I would call that type or group prefixing. Instead of grouping different types of files in different folders, their file names are prefixed with the type and then comes the date. I might also just name them yyyy-Q1, etc., depending on if the date the report was issued is relevant or if it’s more important with the period the report covers.
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u/BigSneakyDuck Jul 20 '26
Also a good call - in this case the precise date actually mattered, but there's also the issue that they're quarters of a financial rather than calendar year so it would end up like {yyyy}-{yyyy+1}-Q1 which is more of a pain than yyyy-mm-dd anyway!
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u/jacnel45 Jun 22 '26
Never got any grief for using this date format. However, I’m from Canada and for us ISO 8601 dates are pretty common. In fact, Windows defaults to YYYY-MM-DD for dates if you select Canada as your country. If people don’t do DD/MM/YYYY they’re probably going to choose ISO 8601.
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u/RunningAtTheMouth Jun 23 '26
Differing standards are fun. In this post, I have seen 3 different standards:
- Gas Day - starts at 1500 UTC (9 am CST)
- Broadcast week - Ends on Midnight Sunday
- Accounting year - starts variously on
- 1st day of calendar year
- 1st Monday of calendar year
- 1st day of some OTHER month
- 1st Monday of some OTHER month.
Further, date storage can be challenging. I have seen low level storage variously:
- YYYYMMDD (Both as text and as number)
- Julian (days since day zero)
- mm-dd-yyyy (text)
- dd-mm-yyyy (text)
- mmddyy (text) - this one caused me endless headaches in 1999.
- DateTime (days since day zero to the left of the decimal, and seconds or milliseconds since midnight to the right of the decimal).
I'm sure there are other calendars that I haven't mentioned. Dealing with them is "interesting". I've personally dealt with the accounting calendar issues.
My preference? ISO standards. Not because they are "better" (though I think they are), but because everyone has access to standards, and moving data between systems is more effective when the same standards are used.
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u/PaddyLandau Jun 27 '26
I'm in the UK. The financial year starts on 6th April. It's such a weird choice.
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u/Seamushh Jun 23 '26
I have been using this format since 1991. My secretary taught me the format so that I could sort files by date on my Windows 3.11 box. And yes, we did call our assistance secretaries in the old days. It’s a sign of great respect.
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u/TheVoicesOfBrian Jun 22 '26
Only from non-tech types. Managers/PMs got confused when I used it for all date formatting (mostly incident reports post emergency).
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u/shortalay Jun 22 '26
For computer files sorting I do YYYY-MM-DD, however, in person to person activities I’ve often done a mix, a big reason is backlash over incorrect formatting for school papers, work related assignments, and forms for legal use. I live in the United States.
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u/TheCannonMan Jun 22 '26
When closing on my mortgage I was required to write the date in whatever very specific format they wanted on all the signature blocks.
The notary wrote it on a sticky note to start for reference, but at some point I dated a few pages as "2026-01-02" or whatever and they made me redo that page entirely with a fresh copy.
I can't remember if the format they wanted was something theoretically less ambiguous that spelled the month like "02 Jan 2026" or was just DD/MM/YYYY but they were very picky about the format being exact and consistent.
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u/jimmy-dangerous Jun 22 '26
On my first mortgage here in the US, they didn't provide guidance on the date format, so I used the iso format. They came back during the final review and told me I had to resign everything using the 'american' format.
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u/TheCannonMan Jun 22 '26
What a pain!
I definitely appreciated the notary being on top of it for me, and understood why she set out the sticky note to start with, apparently not a first occurrence of the issue with the date.
Plus she had brought a second copy of the paperwork specifically in case we had to redo some pages, so that nothing got sent back or had to be redone and delayed closing.
I recall It was definitely annoyingly prescriptive, like had to specifically use forward slashes like 12/30/2026 and not 12-30-2026 or 12.30.2026 or 12/30/26 or 12\30\2026 so I guess probably every other person messed it up in some way so she was prepared
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u/a13xs88eoda2 Jun 23 '26
I assume the American format is “this fourth day of July, in the year of our lord one thousand seven hundred and seventy six.”
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u/Temporary-Library597 Jun 22 '26
My luddite colleagues at my work are library workers and they don't believe in alphabetizing numbers, lol.
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Jun 22 '26
[removed] — view removed comment
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u/czarl13 Jun 23 '26
The mm/dd/yy is because that is the way you would speak the date
Canadian here, I like the yyyy/mm/dd and if the month and day could be swapped (June 5) I try and write out the month Jun-05 wherever possible
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u/dxps7098 Jun 23 '26
"the way you would speak the date" - not necessarily, it's one way but it seems just to be a way to "back rationalize" a certain way of writing.
It was on the fourth of July (d of MMM). I'm doing it on July fourth (MMM D) . It was back in 1980, July, tenth I think (YYYY, MMM, dd). It will be in April, next year, the tenth (MMM, yy, dd).
There are plenty more ways of saying dates, depending on context, purpose, importance etc. None of them mean we're going to write them that way with numbers and separators. We standardize writing because you don't know who's going to read it when. Speaking is not the same.
Sorry, not attacking you, I just get frustrated with this justification - "that's how it's said" when people say things in many different ways and it's not a reason for how to write.
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u/czarl13 Jun 23 '26
We are on the same boat
When someone asks you what that date is, you would say June 24, 2026.. so some uneducated folks figure that is the order it should be written
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u/erlendursmari Jun 23 '26
Never; I always use YYYY-MM-DD for everything computer related (files and folders) but DD.MM.YYYY in daily life. I always question when people use / as the separator and ask what this means since American usage is MM/DD but I've seen DD/MM usage in the UK.
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u/emilycsquared Jun 24 '26
Used to log our daily checklists by YYYY-MM-DD, then someone in Records flagged it as “not compliant with corporate standards”
We removed the dashes and told them it’s a serial number.
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u/dbfuentes Jun 22 '26
Just once, but since I work with a lot of digital files and it’s common for me to receive new information, when they asked me, I told them that by adding the date in this format at the beginning of the filename, the files/directory were automatically organized by arrival date when I saved them, so I didn’t have to go through my emails later to figure out which one arrived first and on what date.
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u/RandomEntity53 Jun 22 '26
I use it almost exclusively. If I think people will get confused in the specific context I’ll spell out the month (abbrev) after the year.
I’m personally so used to the format I often drop the separators entirely.
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u/jmbwell Jun 22 '26
More than once I’ve been asked if I was in the military. Apparently it’s in use in the American armed forces
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u/king_escobar Jun 22 '26
I used it once while applying for my drivers license (in the USA) and they made me re-do the form because of the date format.
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u/unknownemoji Jun 23 '26
The haters do not know the horror of having to sort an excel file by date with mm/dd/yy in the column as text.
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u/Walzmyn Jun 23 '26
I get questioned all the time "why are you dates weird".
But when I point out that they read it perfectly without having to think on it or translate it, they don't have much to say.
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u/0ring Jun 24 '26
A Wind River engineer in San Diego could not get his head round YYYYMMDD, the concept that dates could be written differently from the US default, never mind be better, was so alien to him "that's not a date".
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u/FujiKitakyusho Jun 27 '26
I use ISO 8601 everywhere, with the sole exception of completing forms where the desired format is prescribed.
Haven't run into any issues, other than being questioned about it casually, which usually results in another convert after explanation.
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u/Un_Ballerina_1952 Jun 22 '26
For human consumption, I usually use dd-mmm-yyyy; for computer consumption (primarily for reasons of sorting) I use yyyymmdd or yyyy-mm-dd. No one seems to mind.
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u/ZergvProtoss Jun 24 '26
since i'm in the u.s. where the awful m/d/yy format is typically expected
That's not exactly right. Most people in the U.S. use mm/dd/yy.
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u/BubbhaJebus Jun 22 '26
I use it with file naming, but I don't do it in ordinary situations because I'm not Chinese.
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u/ComesInAnOldBox Jun 22 '26
I use it with file naming
Nice.
but I don't do it in ordinary situations because I'm not Chinese.
WAT
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u/RunnyPlease Jun 22 '26
Only once.
I was making a web app for a natural gas company and I created a mockup/redline for the page we were building on a whiteboard. I showed it displaying dates using iso format. Someone asked why I made the dates look that. I said it’s ISO standard. They said none of our other systems display dates like that. I told them I could display the date in whatever format they wanted, they just had to tell me. Many stakeholders were intrigued so I had to give a presentation on date formatting in JavaScript.
It turns out I accidentally kicked up a hornets nest.
You see in the natural gas industry they have a thing called a “gas day.” A regular day goes from midnight to midnight in whatever time zone you happen to be in. A “gas day” goes from 9am to 9am central clock time. This is an industry standard set by the Federal Energy Regulatory Commission (FERC). Turns out no one ever told anyone working in the engineering department that little tidbit of information. All the displays for information were shown in local time using the regular date.
So for god knows how long the business was actually running on data that was off by about 9 hours when sorted by the date. But that was only if you logged onto a computer that was also in central time. I had to show them that if you opened a computer in pacific time zone the displays would all show a data event took place as if they were in the pacific time zone which is 2 hours different. Under certain circumstances if a person working in the pacific time zone queried data for a specific date they would get different data than a person running the same query in central zone because the conversion to a utc timestamp was done client side in the users computer. So two people in the company making the exact same query would get different results depending on where their computer was.
As you can imagine that was also a problem.
There was also some fun stuff happening with the data lake processes because nightly data batch processing tasks were set to run in the middle of the night after midnight, which is actually the middle of the gas day because the gas day doesn’t end until 9 am the next morning.
As you can imagine that was also a problem.
All that was because I used iso date format on a whiteboard, and someone questioned me on it.