For example, my friend's anniversary is on 3rd August (03/08/2016-dd/mm/yyyy). If I interchange the Month and Day digit and write 08/03/2016 meaning 8th March, is there any special word for this kind of date in English? Like 'Reverse Date' or something. Ignoring the dates after 12th.

Editing: I am not confused about date formats here. Think it like, If I want to wish my friend on 8th of March (instead of 3rd August), what should I say him? Like: 'Happy Reversed Anniversary'!?

  • 3
    @Lawrence, no, I wrote it intentionally.
    – Ankur
    Mar 8, 2017 at 10:46
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    @tchrist There goes the Fourth of July. :)
    – Lawrence
    Mar 8, 2017 at 14:40
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    @tchrist Thank you kindly. I hope the graduation went well, but I'll have to offer my apologies as unfortunately the invitation was held up in the post. My compliments on the excellent formatting of your dates.
    – Lawrence
    Mar 8, 2017 at 15:18
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    As a fan of portmanteaus, I think you should wish them a Happy Anni-Reversary.
    – cloudfeet
    Mar 8, 2017 at 16:04
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    I recommend switching the expression of the dates in the question from dd/mm/yyyy format to yyyy-mm-dd ISO date format, to make it clearer that US format has nothing to do with the question, and that the result of this process is not intrinsically in US or any other format. Mar 8, 2017 at 17:40

5 Answers 5


While it's difficult to prove a negative, having grown up speaking English and being fairly well-read, I feel safe saying:

No, there is no commonly used word for this that would immediately be understood by the majority of people.

  • @Josh OP isn't asking about the name of the format
    – Rob K
    Mar 8, 2017 at 15:50
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    @Josh, see his edit. He's asking if there is a term in English for when a date represented as mm/dd/yy is also a valid date if interpreted as dd/mm/yy.
    – Rob K
    Mar 8, 2017 at 15:55
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    @Josh He's not asking about the name of the date format, he's asking about the name of a joke/intentional misuse of date formats
    – Izkata
    Mar 8, 2017 at 16:10
  • @Josh: US date format does not appear in the question. All dates are explicitly in dd/mm/yyyy format. Date formats are not relevant. Mar 8, 2017 at 17:29
  • @Azor-Ahai: No it's not: "If I interchange the Month and Day digit and write 08/03/2016 (dd/mm/yyyy)". Mar 8, 2017 at 21:28

Middle-endian date format appears to be the technical term, more commonly known as the US date format, see also Ngram:

  • Despite the variety of date formats used around world, the US is the only country to use the mm/dd/yy format.

  • This condition is diagnosed as middle-endianness. Seriously. It comes from computer science where bytes are arranged according to their size. If the order has larger ones at the front, it's known as big-endian and so too are dates formatted with the years first (see the likes of China and Mongolia in the map).

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    This is quite useful @Josh, but date format is not my confusion :)
    – Ankur
    Mar 8, 2017 at 10:53
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    @Ankur Well, you could say "Happy Middle-Endian Birthday".
    – Andrew Leach
    Mar 8, 2017 at 10:55
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    Fascinating map!
    – Dan
    Mar 8, 2017 at 14:24
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    @Josh: The question is asking whether there's a word for the new date obtained by switching the day and month numbers of an old date (not the new representation of a date obtained by switching the positions of the day and month numbers in the old representation of a date). Mar 8, 2017 at 17:42
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    This is a good answer to a different question, and would be upvoted if that were the question.
    – DCShannon
    Mar 8, 2017 at 17:46

A possibility would be to call it a "transposed" birthday.

  • 1
    Not a bad idea, but as it stands this isn't a good answer. It would be much improved by a definition of "transposed" and a reference/link for where you got that definition from.
    – AndyT
    Mar 8, 2017 at 17:15
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    Transposed date is the typical term I use and hear when dealing with data entry systems and the people that use them. It's a bit ambiguous though, because besides month/day transpositions, there are also day transpositions (1/21/2017 vs. 1/12/2017). Without more specific language though, if I just heard "transposed date" I would be assumed to be month/day. Mar 8, 2017 at 18:33
  • Accepted @Kevin's answer as 'transposed' can create ambiguity, but +1 for now, I'm wishing him 'Happy transposed Anniversary' :)
    – Ankur
    Mar 9, 2017 at 10:32
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    @Ankur Although your question has nothing to do with date formats, seeing as month and day do get transposed on crossing the Big Pond between the UK and US, and seeing as there is no real word for what you want, how about calling it a "transponded" birthday?
    – bof
    Mar 9, 2017 at 11:53

As a tongue-in-cheek in joke, I'd call this a:

UK Birthday - if you're normally using mm/dd/yyyy and transposing it to dd/mm/yyyy.

U.S. Birthday - if you're normally using dd/mm/yyyy and transposing it to mm/dd/yyyy.

These aren't widely used or 'correct' by any reasonable way, but in a joking sense I think a friend or colleague would get what you're doing in context. "It's your U.S. Birthday today!"

  • Or even "Happy American Anniversary" ;-)
    – Rycochet
    Mar 9, 2017 at 12:04

As has been mentioned in other answers, there's no universally understood word that I can think of (native US English speaker).

However, colloquially and in business, I've seen the dd/mm/yyyy format referred to as the "European Format"/"European Date Format".

So, you could perhaps congratulate and say "Happy European Anniversary!"

(Here's at least one use of "European Format" in practice.)

(Also, it's a little more special for those folks who got married/started dating/whatever in the first 12 days of the month. If you were married July 13, you don't get a "European Anniversary" in the US format since 13/07/20xx never comes up. )

  • 2
    OP is the other way around - dd/mm/yyyy standard, and looking for an alternative name - the mm/dd/yyyy format is almost exclusive to the USA - en.wikipedia.org/wiki/Date_format_by_country
    – Rycochet
    Mar 9, 2017 at 12:03
  • @Rycochet - D'oh, then yeah I'd go with "USA Birthday" or "USA Format".
    – BruceWayne
    Mar 9, 2017 at 15:02

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