[Clue: he was born three weeks ago, on 23 September 2014.]

Originally, as I understand it, the word birthday meant the day of one's birth. It was a one-off event.

I don't want to quarrel with the idea of extending this to cover anniversaries of one's birth. I'm comfortable saying that I've had forty birthdays, or thereabouts.

I'm not sure how far back the concept of celebrating the anniversary of one's birth goes, but it at least pre-dates Moses (Genesis 40:20), and therefore long pre-dates the English word birthday. This isn't a question about how that custom arose, but about the way we use the English word birthday and whether it makes sense. Does it refer to the day of one's birth, or an anniversary, or both?

Convention seems to dictate that my son's first birthday is when he's a year old; his second birthday will be when he's made it through another year; and so on. Now this is odd: if his first birthday is in a year's time, what's become of the day of his birth? Is this now considered not to be a birthday at all? I'd have expected him to become a year old on his second birthday, and so on.

In summary, the language drift seems to have gone like this:

  1. notion of birthday = the day of one's birth;
  2. notion of birthday extended to include anniversaries;
  3. notion of birthday now restricted to exclude the day of one's birth.

Is this a bit weird, or what? Has it just happened so that the cardinals (four years old) line up with the ordinals (fourth birthday)?

Is it because birthday is now shorthand for anniversary of one's birth?

Am I missing something?

  • Comments are not for extended discussion; this conversation has been moved to chat.
    – Andrew Leach
    Commented Oct 9, 2014 at 21:34
  • When answering, please bear in mind that this is English.SE. Different cultures may be different, but only English-speaking cultures and their use of birthday is relevant here.
    – Andrew Leach
    Commented Oct 9, 2014 at 21:38

7 Answers 7


I can't speak to the history of the usage, but basically, yes, "birthday" means the anniversary of your birth, not the original day of the event. People rarely refer to the day someone was born as his "birthday". Rather, we call that "the day he was born". If you want to know the date someone was born, including the year, you don't ask, "When was your birthday?", you ask, "When were you born?" If you asked someone, "When was your birthday?", they would be much more likely to answer "Last Thursday" or "That was way back in March" than "1963". When someone who is designing a form wants to know the day and year you were born, they don't label the space "Birthday", they label it "Date of birth".

Given that, it makes sense to call the day one year after a person was born his "first birthday", a year later is his "second birthday", etc. Just like we say that one year after you are married is your "first anniversary", etc.

As I say, I don't know the history. I don't know if English speakers ever called the day that someone was born his "birthday". Whether it started out that way and the meaning has shifted, or whether "birthday" has always meant the anniversary of one's birth, I don't know. According to http://etymonline.com/index.php?allowed_in_frame=0&search=birthday&searchmode=none, we get the word from an Old English word that referred to an anniversary, not the original event. So maybe that means it was always an anniversary.

  • 18
    +1 - So prevalent that in many documents, birthdate is marked as date of birth, shortened to D.O.B. When questioned (in an official capacity, the question is simply, "Date of birth?" No doubt because if asked "Birthday?" people just say "January 1st" (or whatever). Commented Oct 6, 2014 at 15:02
  • 7
    The common sense method to on forms that use birthday is to check whether there is a field for year or not. If they ask for a year, they're obviously looking for your date of birth (since an anniversary occurs every year). With no other context, birthday to me is the anniversary, not the original.
    – Gob Ties
    Commented Oct 6, 2014 at 15:28
  • 5
    BTW If you used "birthday" to mean the original event, it's not clear what a "second birthday" would mean. Unless you believe in re-incarnation. Well, I suppose there is John 3:4.
    – Jay
    Commented Oct 6, 2014 at 16:25
  • 10
    Isn't there a joke to that effect as well? Something like: Q: "What is your birthday?" A: "June 6" Q: "What year?" A: "Every year." Commented Oct 6, 2014 at 17:10
  • 4
    @DavidMulder The problem with those two examples are that they are muddled with UI/UX considerations. To whit: you are not just presented with "Birthday:" and a blank, you are presented with three fields, for day, month, and year, making the implied request for DOB clearer; and yet, year is optional. They don't expect to get DOB there, they expect to get either birthday or DOB, and they'll accept either. They are overloading the meaning of the form for UX reasons, adding a confounding variable that make them much less useful as examples about a purely linguistic point. Commented Oct 8, 2014 at 6:37

Your son's first birthday will be 23 September 2015.

23 September 2014 was his zeroth birthday. Like C arrays, laws of thermodynamics, and the days of March, birthdays are zero-indexed.

  • 9
    I don't think this is how ordinals work. Your C Arrays link, for instance, says this: "The first element of the array above is point[0]." Note the language: it's zero-indexed, but the first one is number zero. If this really is analogous, then my son might have had birthday zero a couple of weeks ago, but this would have been his first birthday, number 0. Commented Oct 6, 2014 at 18:47
  • 4
    Nonetheless, if you say "first birthday", most listeners will assume your son has been alive for 365 (or perhaps 366) days, and if you say "zeroth birthday", people will know what is meant.
    – tobyink
    Commented Oct 6, 2014 at 19:44
  • 2
    Sure, I realise this is how the words are generally used (though I have a feeling people would understand, but also look at me funny, if I said "zeroth birthday"). Commented Oct 6, 2014 at 20:36
  • 1
    @tobyink: The purpose of a birthday is not so much to mark a moment in time as to mark the passage of the preceding year. The first birthday marks the end of the first year. This is a different situation from C array indices, which mark the location of the start of array elements. The first array element sits between index 0 and index 1; the next element between index 1 and index 2, etc.
    – supercat
    Commented Oct 6, 2014 at 22:32
  • @supercat: Off-topic, but in computing, there is a difference between element and subarray. 0-th (first in colloquial speech) element is exactly at index 0; the subarray containing the first element is between 0 and 1. It is the difference between fenceposts and fences between them: the 0-th fencepost is at fencepost #0, but the 0-th fence is between fencepost #0 and fencepost #1.
    – Amadan
    Commented Oct 8, 2014 at 2:35

I stumbled upon that some time ago while coding, after all naming convention is very important to proper software architecture :) My conclusion was, birthday = anniversary, birthdate = date of birth.

You can understand this if you are familiar with the concept of abstraction - what is a day if not a date without a year (Independence Day, Labour Day, etc)? and what is a date if not a day with an explicit year? (Independence Day 1975, Labour Day 1975, etc)


A date specifies a day for a specific year

A day specifies a date independent of year


Birthdate = 22/06/1962

Birthday = 22/06

It makes sense to use birthdate for the day your son was born and birthday for that day in whichever year - which coincide with the celebrations (including the birthdate).

Very nice question :)

  • 2
    came to post this. Commented Oct 7, 2014 at 21:33

There is no reason to think that birthday is shortened from anything. There are several phrases with day which mean "anniversary" or "commemoration" - name day, saint's day, Independence Day. Birth day (as a phrase) fits in to this pattern.

The first meaning given for birthday in the OED is "the day on which anyone is born" (with transferred and figurative meanings), and it is not marked as obsolete. But the latest example given is from 1858.

The second meaning is the familiar one of "The anniversary or annual observance of the day of birth of any one", with the first example around the year 1000, and the first securely dated example from 1382.

So in answer to the question, I don't think there's anything odd about the numbering: the usual meaning of word is the anniversary.

  • That is correct. But do note that the OED article was published in 1887. So the fact that the latest example is from 1858 does not really tell us anything about whether it is obsolete or not.
    – fdb
    Commented Oct 6, 2014 at 23:00

"Birthday" is really a shortened form of "anniversary of the day of birth", so the day you are born is not an anniversary of that event. We do use the phrase "birth day" to mean the day of your actual birth.

To add to the confusion, occasionally "birthday" does mean both your birthday and the year of your birth -- on official forms for example -- but you have to allow the context to determine.

A thing to remember is that etymology does not equal meaning. On the contrary, derived words often take on a whole new set of meanings and implications by themselves. For example, the etymology of "pineapple" is plain, however, the resemblance between that fruit and a pine cone or an apple is very limited.

Similarly, the verb "understand" also has a fairly plain and obvious etymology, but the word has a whole world of meanings beyond the original figurative derivation.

In terms of "birthday", etymonline has this to say:

Birthday late 14c., from Old English byrddæg, "anniversary celebration of someone's birth" (at first usually a king or saint); see birth (n.) + day. Meaning "day on which one is born" is from 1570s. Birthnight is attested from 1620s.

I think the reference to the use of religious saints' birthdays is particularly relevant, since presumably they are dead by the time we celebrate their saintliness.

And on the matter of the birth day of your son, congratulations! There is no greater moment that seeing him take his first breath, and you are about to embark on one of the great journeys in life, full of joys, fears, surprises, difficulties, and every human emotion imaginable. I am sure your life is about to become much fuller, and much busier.

I offer you my best wishes on this special occasion of your life.


The anniversary of your son's birth date is your son's birthday. The date of birth of your son, or birth date, is on 23 September 2014.


An example of "birthday" being used to refer to the day of birth is when people say something like: "I was wearing my birthday suit.", meaning they were naked.

That term doesn't seem nearly as clever now as it did before I read this thread.

  • 2
    +1, very nice example. (I'm just glad your profile pic is an abstract icon rather than a photo.) Commented Oct 7, 2014 at 12:50

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