Ahrefs URL Rating (UR) is a metric that shows how strong a backlink profile of a target URL is on a scale from 1 to 100. Please note that this scale is not linear — meaning it’s easier to grow your page score from UR 20 to UR 30 than from UR 70 to UR 80.
Generally speaking, each page passes its rating score to all the pages that it links to. Note that only do-follow backlinks are taken into account.
Imagine that a given page has 10 do-follow external links and its URL rating is 100. This page will pass a part of its UR, equally divided between all 10 pages it links to.
So the more external links there are on the referring page, the less “link juice” will be passed to every page it links to.
Still, it’s an oversimplified version of how our algorithms calculate the UR metric as they take lots of other factors into consideration.
To sum this up, the more high quality backlinks a given URL has, the higher its UR score is. Remember that some backlinks pass more of “link juice” than others. (You can read more about what makes a backlink high quality here.)
It’s also worth noting that our algorithms are able to spot and cut off the so-called "linking loops" — the practice of exchanging rating scores again and again on a loop between two websites.
As our backlinks database gets updated every 15 minutes, the UR scores are also updated to include the latest changes.
However, it doesn't mean that each individual UR score will be updated every 15 minutes: in some cases, our system needs a bit more time to adjust rating changes in the database.
People often think that Ahrefs URL Rating is similar to Google PageRank, but these two metrics are not exactly the same. Indeed, we have started out with a PageRank-like formula, but since then, we’ve changed our UR algorithms a few times to create a metric that would have the highest possible correlation with Google rankings.
More details here: Ahrefs’ SEO metrics explained.