Date format

Let me start by saying that using mm-dd-yyyy is just plain wrong. No really it just doesn’t make any sense to me. Neither does it make any sense to most people world-over if you go my the date-format map up at

If one uses dd-mm-yyyy it makes sense because it’s in decreasing order of granularity (kind of LSB first). yyyy-mm-dd makes ever more sense because

  1. It’s in decreasing order of granularity
  2. Natural ordering in many ways like telephone numbers (country-code, area-code, local-code, number) or IP address
  3. String sorting automatically sorts by that date. E.g. I can easily have folders/files named in this order and DIR lists them nicely sorted out (yea I know I can sort by date/time as well).

d:\MyStuff\Personal\Pictures>dir 2010*
Volume in drive D is Data
Volume Serial Number is 3657-F386

Directory of d:\MyStuff\Personal\Pictures

06/17/2010  01:06 PM    <DIR>          2010_0501
06/17/2010  01:07 PM    <DIR>          2010_0504
06/17/2010  01:16 PM    <DIR>          2010_0508
06/17/2010  01:20 PM    <DIR>          2010_0509
06/17/2010  01:24 PM    <DIR>          2010_0515
06/17/2010  01:29 PM    <DIR>          2010_0517
06/17/2010  01:30 PM    <DIR>          2010_0523
06/17/2010  01:33 PM    <DIR>          2010_0528
06/17/2010  01:37 PM    <DIR>          2010_0529
06/17/2010  01:43 PM    <DIR>          2010_0605
06/17/2010  01:47 PM    <DIR>          2010_0606
06/21/2010  08:40 PM    <DIR>          2010_0616
06/28/2010  10:33 PM    <DIR>          2010_0619
               0 File(s)              0 bytes
              13 Dir(s)  55,925,829,632 bytes free

But I just cannot fathom why would anyone use mm/dd/yyyy. In what way is that intuitive?

Comments (7)

  1. Harsha says:

    Absolutely. It is someones mistake that is just over living despite causing so much of confusion.

    I guess YYYY-MM-DD makes more sense than DD-MM-YYYY, because when we combine date with time whole thing should mark the time in a uniform manner.

    Does  DD-MM-YYYY HH:MM:SS  make proper sense?

    Date in ascending format and time in descending format.

    Thus I feel it makes more sense with YYYY-MM-DD HH:MM:SS ~

  2. BarfieldMV says:

    I guess that having the date first as a number in a agenda request of on a invitation when you already know its this month/soon you don't have to read the rest of the date.

    This month the 12th is easier to read that


  3. It's no different from sorting names in many Western cultures: Given "Firstname Middlename Lastname" the Lastname is the primary sortkey, with Firstname as secondary and Middlename as tertiary.

  4. mm/dd/yyyy is intuitive if you read it in English aloud. 03/02/10 then becomes March 2nd, 2010. Obviously, it doesn't make any sense if you don't speak English.

    Same thing with dd/mm/yyyy. For most human that's more logical and intuitive than yyyy/mm/dd because in our day to day live we care about what happened in the past few and next days. We rarely need to know what we did at this very day one or more years ago. Hence, we put the most important piece first (the day).

    This has actually become a convention when looking at e-mails, comments, or any time dependent information. You often only see the time and know it's from today. Or it says Jul 16, and you know it's 07/16/2010, because whatever this date refers to happened also in July 2010. Only for pieces older than a year we see the full date.

  5. Chirstof even for people speaking english Inatively I hear them say the other way around. E.g. in US the independence day is referred to as 4th of July, so day comes first.

  6. Adrian says:

    In the end it depends what you would like to stress – is it the month, the day, the year of occurence or the order the events occured on the timeline. If it's the later then, as you stressed, the ISO 8610 date (…/ISO_8601) could be a better choice, especially because it allows to use the lexicographical sorting also with dates.

    Natural representation or ordering are vague terms whose meaning depend on context – and this includes standards or habitude, fact that could make it differ from country to country, as stressed also by the above comments, or even to smaller geographical or organizational scales.

  7. Ratnakar Dutt says:

    You are true. it's so much of confusion. especially for the people who with different clients or extended teams around the world.

    I personally prefer writing dd-MMM-yyy. 14-Oct-2011. It woun't be any confusion.

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