I do understand that citations should be as precise as possible (including e.g. edition of a book or a page number), so that ideally, the reader can find the information exactly as I found it when writing.

I also understand that the problem with citing webpages is that they can change. But how does including the date when I accessed the page help anything? The reader still won't be able to read the same version I did (unless the page includes history, which is very rare). And comparing the accessed date with the current date isn't very helpful either: some webpages change multiple times per day, some aren't modified for years.

Or is the accessed date useful for some other purpose?


5 Answers 5


I am not aware of any published accounts of how style rules are developed. If you really want to know why a particular rule was developed, you need to ask them directly. That said, there are a number of different styles for dealing with electronic materials and these styles are changing:

  • MLA: You always need the date of access for electronic resources.
  • APA: You rarely use the date of retrieval, although in previous versions (APA 5) you always did
  • CMS: You never need the date of access/retrieval. I am not sure if you ever did in earlier versions.
  • 4
    This answer really doesn't address the OP's underlying question. It essentially says: "i don't know, ask someone else..."
    – Paul
    Dec 5, 2014 at 4:04
  • 4
    @Paul my point was 3 of the big players in terms of style guides recommend different things and at least one of them recently change its view. To me this means there is no definitive answer.
    – StrongBad
    Dec 5, 2014 at 8:39

A URL does not refer to content, it is only an address. Since you are making a claim about what was written at that address, you must associate a date with it, or it is meaningless.

If you do such a thing, you should also save the content, in case it is not recoverable and you want to refer to it again or support it further.

  • 1
    So you're saying it's important to uniquely identify what I was reading and it doesn't matter whether anyone else will be able to read it too?
    – svick
    Jan 4, 2013 at 18:35
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    Not that access doesn't matter, just that uniqueness does. Jan 4, 2013 at 18:39
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    +1 It is really about identification. So sure, there are cases when the date is not necessary, DOI is one such for example (it's moreorless just a web address, but its contents should be stable in time).
    – yo'
    Dec 4, 2014 at 22:20
  • The content you get can depend on other factors than just the date. URLs often produce different content depending on your IP address, your user-agent, and cookies. It is even possible for a page to be written in different languages and automatically have it delivered in the language, which the user chose in their browser.
    – kasperd
    Dec 6, 2014 at 22:41
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    @kasperd While that is certainly true, there is a limit to what is reasonable for an author to check. The types of sites which publish facts which are relevant to academic expositions would rarely contain this type of dynamic content generation, though if that changed, the rules would absolutely have to adapt, too. If you are citing primary sources on very volatile sites (say, Tumblr or 4chan), probably you need to take more precautions to ensure that the original source can be recovered.
    – tripleee
    Jan 28, 2022 at 12:21

If you know the URL and date, you may be able to use The Internet Archives (a.k.a. the Wayback Machine) to see the page, if it didn't change too frequently.


Most URL cited are institutional sources, the kind of guys that can provide reliable information*. If a reader finds that your claim does not coincide with the information they can find at the moment, they can contact the administrators of the page and ask. Certainly, it is easier to get the correct copy if you have an specific date.

In Bioinformatics it is common to use web servers to run some programs (example). In this cases, the dates are important for replicability, even when citing the program version, because the specific software versions it depends on may not be public (say, before March 15th, AwesomePredictor.com had installed BLAST+ 2.1, and after then they installed v2.2).

  • One could cite less formal sites to support side points like "this and that have been in the focus of popular culture", but these are ephemeral by nature.

I found an answer directly from a style guide. According to the APA Blog (6th edition),

[W]e usually don’t ask, “When did you consult that source?” One exception to this rule would be for material that is subject to frequent change, such as Wikipedia entries. Because this information is designed to be constantly updated, it’s important to let readers know when you retrieved it.

You can check the revision history of Wikipedia (though usually a poor academic source) but it isn't the only site that has a public record like that. Stack Exchange sites do too, as do many software documentation sites (through GitHub). Still other sites have private revision histories that an admin has access to. (For example, WordPress sites.)

Another answer brought up archival sites like archive.org. If the page wasn't updated, but the URL no longer works, then most likely you will only need to check one entry to find the information: the first. (You may also be able to search the internet instead to see if the page moved by using the other details, namely title and author.) But with a frequently updated source, it's possible that the cited information only appeared in a single revision of the page. Without knowing which, you'd have to check every snapshot (excluding those after the citation was published). And with an external archival site, the page could have changed between snapshots, so it's a good idea to save the page yourself if you're citing it. However, the comments on the APA article indicate that they believe archival sources to be secondary sources, so the URL of the original is what should go in the citation list.

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