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tldr: "dunno"
I find it mildly infuriating when an article is titled in a way you think you'll find an answer, and it is actually some rambling ending up saying we don't know...
This is because questions on hacker news are usually rhetorical.. This title is actually right on point, if there was an answer in the article it should have been: Why Americans write the month before the day.
The real reason is that I guess less people would be clicking on "We don't know why Americans write the month before the day".
If there's one area where the rest of the world can learn from China, it's this: yyyy-mm-dd.
Yeah, it's weird that people try to justify being completely backwards by pointing at someone who's half-backwards. YYYY-MM-DD is the only way that makes any real sense.
Anyone who has ever organized a file system by date knows that yyyy-mm-dd is the only way to go.
Until I read this article, I never realised where the term "endianness" came from:

"...computer scientists got their inspiration for the term 'endianness' from Jonathan Swift's 1726 epic Gulliver’s Travels. In the fictional kingdom of Lilliput people have to open their soft-boiled eggs at the small end (it's a royal decree). While in Blefuscu, eggs are cracked from the other end. Lilliputians are small-endians while Blefuscudians are big-endians."

When I'm arranging my photographs in folders, I prefer yyyy-mm-dd. That way it stays in chronological order.

However for casual reference, when year is not needed, I find dd-mm more intuitive. I guess it has something to do with reading from left to right... at a glance, it's just easier to comprehend.

I've always found mm-dd a bit odd to use.

It's an international standard: https://en.wikipedia.org/wiki/ISO_8601
There are two ways to send dates across the wire as text between different systems:

1) ISO 8601

2) A world of hurt

Source: experience. Not using the standard invites things to break, but only on a some machines, and only on or after the 13th of the month. Of course the data for the first few days of the month will be present, just wrong.

And sadly there are still things that insist on using the second option. RFC 2822 used in MIME (historical oddity because it pre-dates ISO 8601), UNIX timestamps as either seconds or milliseconds (at work we have one instance where numbers > 32 bit are serialized as a hex string in JSON, which includes such a millisecond-UNIX-epoch timestamp), etc.

Slightly related insanity: Using localtime (i.e. not UTC) for log timestamps. And then having fun once a year dissecting the one hour that has twice as many messages.

It's annoys me that the time format with colons means I cannot use it for file names. What do you use instead?
Some other innocuous separator character such as underscore, or none, just fixed lengths for the numeric fields. But always, yyyy mm dd order.
Underscores work well, which results in "2013-12-16 10_22_57Z". I can still somfortably read it, at least.

Hyphen-minus would lead to too easy confusion with the date part. Fixed-width fields can be hard to read.

I just use HHMM at the end (or HHMMSS if you need that precision).

Ex: 2013-12-16_1741.txt and the like.

> When I'm arranging my photographs in folders, I prefer yyyy-mm-dd. That way it stays in chronological order.

It is kind of interesting to think about that from a usability perspective, because the "stays in chronological order" refers to how most file system browsers default to sorting things by name. If it was a concious decision to sort by name, then the description would be something more like, "when I am sorting my folders by name, I'd rather sort by date, so I put the date in the name."

Folders do tend to have Date Created metadata, so in theory you could "sort folders by created date" rather than by name, but where that data is stored and how that data changes as the files are moved around is pretty opaque, so it makes lots of sense to not rely on it.

Date created might not match the metadata date for the content. For example, you might download a bank statement for november, in december.
When I'm copying/modifying/mirroring folders across platforms, the date in metadata can get messed up. However, a name like "2013-02-22 Trip to Tahoe" is what I find most useful. Each folder has a mnemonic & I can search/browse my pictures chronologically when I'm feeling nostalgic :)
Sometimes the natural-seeming title of a document includes a date, but it isn't the creation date (simple example, scanning a letter or invoice). Would you suggest frobbing the metadata?
The advantage of using yyyy-mm-dd, beside the fact it is a standard, is that it is unambiguous. When I read a date like 12-11-2013, I don't know if we're talking about the 12th of november as we French correctly write it, or about the 11th of december as those bloody arrogant US American incorrectly do.

But 2013-11-12 is non-ambiguous since (I guess) nobody uses a yyyy-dd-mm format.

I always wondered why Americans wouldn't read $23,428.32 as "twenty-three thousand dollars thirty-two cents and four hundred and twenty-eight dollars"
More interesting is how people read $1,534

Is it one thousand, five hundred and thirty four dollars?

Or fifteen hundred and thirty four dollars?

Or even one and a half thousand and thirty four dollars?

All of these forms are used in some countries/languages.

The article doesn’t actually answer the question. The month-day-year date format was commonly used in the UK until the 1920s or so, simply because it matches a common order of spoken dates: December (the) sixteenth, 2013. Presumably, Americans just retained the older form while Britain moved on; a similar thing happened with the rhotic General American accent.

(No, I don’t have a citation on hand.)

Although if you or anyone else could come up with a citation, I'd love to read it.
Sounds like a possible reason and explanation. Thx.
> simply because it matches a common order of spoken dates

I'm a native British English speaker and I would say "16th of December" more often than "December 16th".

did you fall through a crack in time from the 1920's?
Same here: "11th January" sounds British to my ears, "January 11th" sounds American.
I thought it was because, to an American at least, the month was most important, then where you are in the month, then the obvious part (the year).
I always thought the common order was: 16th of December, 2013.

You can also argue that it has been that way for a long time. For example, the English King James' Version of the Bible uses dates in the same dd-mm maner (not always including the year), like here:

> "Also on the tenth day of this seventh month there shall be a day of atonement"

Both religious texts and common language influence each other, so I'd say it's safe to assume that some people imitated it in spoken word. I don't know how the other format (December the 13th) may have come about, but my first guess (and that's just a guess) would be that it may have been a good replacement in texts - it sounds good and formal without sounding too religious. Also, as the secularism pushed to move away from the dominance of religious institutions, it might have been an incentive to look for other forms of expressions? Okay, that was a lot of speculation there and I'm probably wrong, sorry! ;-)

I have assumed it was a literation of the way it's often spoken: "January 1st 1980" vs "the first of January 1980"

Article should really have had a discussion of the possible reasons though

It occured to me that having the month before the day is the most practical solution because the most important piece in a date is the month as years change only every 365 days or so, and a day gains meaning only when associated with a month. In other words, the month, being the most salient piece comes first.
Get your logic out of here. We're hating on America.
I disagree that the most important information is the month — it really depends on context.

Most dates I work with are near the present day. Scheduling something next week, referring to last week. Very rarely do I exceed the current month unless I am near a month boundary. The current month is nearly always known information.

In this case, the day is the first piece of information I look for (and almost always when I want to know today's date, all I am really asking for is "what day of the month are we on today?").

I couldn't have said it better myself. I moved to Australia a while back, and I find trying to scan dates on Australian sites infuriating, especially for apartment listings.

11/02/13 12/03/13 15/02/13 14/03/13

So disappointing when you realize the apartment isn't available until next month.

That seems a bit contrived. Whether the month is most salient depends on the context.

And (as a European) I'm constantly amazed by how weird and confusing it is to put the middle-level information up front. If there were different separators (e.g. if today were 12,16/2013) I think I'd struggle less.

What about timestamps from that logic ? I think there, hour is the most important datum, then month, then day, as you state it. Minutes come after that. Year is not that relevant, and seconds are very secondary. So, my comment is written at 11-12-16:59-2013:10 GMT+1. Not very readable for sure, but much more practical ;)
I think that it is as simple as how people say and write dates in full. In the USA people say July fourth most of the time, but in the UK people say the first of May more often. And the year is often not necessary in spoken communication. Especially in daily business where most talk is about short term deadlines "I promised Fred we would deliver by the 4th of June".

Probably if you dig deep enough you will find that some printer of calendars (maybe even preceding Ben Franklin) just happened to print with the month first on every page and that was enough of a tipping point.

> In the USA people say July fourth most of the time

Most of the USians with whom I work say 'Fourth of July'! But then proceed to write it 'backwards'.

Yes, but most wouldn't say 2nd of July or 3rd of July. I feel it is said that way because of the holiday status.
'Fourth of July' is pretty much the exclusive form for the Independence Day of the U.S. and is an exceptional case. It is preceded by 'July third' and followed by 'July fifth'. Even other significant dates usually don't get special treatment, e.g. 'September Eleventh' or 'December Seventh'.
Same reason we say the hour before the minute?
And minute before second? :)
Same reason we say the hour before the minute?

Only if you put the seconds in the middle.

I do know it is easier to validate input data in real-time.

Once you have the month you know how many days the day will be maximum with the exception of leap years when you need to know the year as well. If you enter day then month you could enter a valid day like 31 and then if you enter 11 for November you then have an invalid date.

Either way it is somewhat perplexing and now we have better data entry with the month in words as a drop down in many walks of apps which negate this possible nightmare of 10/11/13 being 10th of Novemeber 2013 or 11th of October 2013. I'm sure many of you have nightmare stories over this date format without even going into the nighmare known as TimeZones.

A: They say "December sixteenth", rather than "the sixteenth of December", so they write it that way.

It's still about as wrong as you can get though.

My favorite part of the article is that the author failed to realize that 'Gullivers Travels' is a satire.
I see from the article that people in the middle east write dd-mm-yyyy But they read right to left. So does that mean that they really write yyyy-mm-dd (like all sensible people should, I might add :-) but read it right to left or that they write dd-mm-yyyy and read it left to right?
This is why I just write everything in ISO_8601. My fellow Americans (excluding my CS colleagues) might think it's a little odd, but there's no room for confusion.
I do the same in Germany and get a few odd looks as well. Strangely though, ISO 8601 was the only official date format here between 1995 and 2001. After that the old DD.MM.YYYY format was allowed again "if the context is unambiguous". I still get questions on why I fill out dates in forms in the sane format, though.
Also, why do they not adopt the metric system of units? (A need to differentiate from the plebs in the rest of the world, perhaps?)
If you order dates within the same year, mm/dd makes more sense than dd/mm. That can be a reason for the American date format. In any case, yyyy/mm/dd makes the most sense.
This page has some pretty good ideas: http://www.reddit.com/r/AskHistorians/comments/1t02dv/why_do...

It probably has something to do with early typesetting where it was much easier to change the number without changing the month if the type was set left to right. This was true for both england and america with the advent of printing but seemed to stick in America possibly due to habit without having a manuscript tradition to fall back on.

Not only does China use the best date format but they also only have one time zone for the whole country and DON't practice DST (summer time). If only the whole world could adopt this policy it would solve a lot of headaches.