Some webmasters are under the impression that they can use nofollow tags on their websites in an effort to prevent pagerank from “leaking out” of their websites. When we know the facts and we look at this, we see that a website cannot benefit based on their usage of nofollow. Basically, your interlinked page’s pagerank won’t be changed whether you use nofollow on some links or not. Pagerank sculpting doesn’t work – and here’s why.
Around 2008 Google changed how PageRank flowed through pages and how nofollow was handled. Imagine a page with two links. If one link was nofollow, you would guess that the other link would get twice the pagerank. Wrong 😀 After Google’s change, the dofollow link would only get half the pagerank from that page. The other half would disappear. This all sounds very confusing, so let’s see a graphic.
As you can see, the links with nofollow don’t allow other links to carry more weight. (Ignore my PageRank values, they are for demonstration purposes and PageRank doesn’t flow exactly like this). The pagerank decay factor causes the “leftover pagerank” which didn’t flow out to “disappear” (or in Matt Cutts’ words, to “evaporate”). Google made this change to prevent pagerank sculpting on websites.