Links pointing to your site will never expire in the eyes of Google, but may become less valuable over time.
You can read more about this over on this post at Search Engine Roundtable.
As we’ve talked about on here quite a bit, getting links to point to your site is a major ranking factor to Google. In general, the more sites that link to yours, the higher you’ll rank.
But what happens when you get a link, and that link still exists three years from now? Does it still count just as much? Maybe.
A user asked this to Google’s John Mueller, and here was his response:
“What does happen though is that, especially if you’re talking about a large website that’s growing regularly, then the pages that links are on over time they get like even deeper and deeper within this website.
So for example, if you have a link from CNN and it’s in an article that’s linked on the homepage, then that’s something that’s really important for us. On the other hand, if this article is maybe a year or two later, is somewhere in the archive at CNN, then that article itself is not something that we would find that important anymore.”
This was a great example with CNN, but is likely true of the majority of the links you get. They’re on the front page of a site due to a new story, but slowly drift into the archives over time. As they head toward the archives, they hold less weight on that site and therefore the link is of less value to you.
This is why it’s important to always be looking for new linking opportunities. If you can build up a good number of archived links, but also have fresh ones coming in, that’s a good clean mix that should really do well for you.