Link juice is a colloquial term in the SEO world that refers to the power or equity passed to a site via links from external or internal sources. This power is interpreted as a vote of recommendation toward your site and is one of the most important factors in determining your site’s search ranking (and PageRank).
There are many ways to earn links from the web through direct and indirect efforts. Direct effort refers to link building strategies, such as document sharing, guest posting, social media marketing, press release publishing and more (click here for some helpful guidelines or watch the video). The indirect effort is gained from presenting excellent content (like guides and infographics) on your site that causes readers to share it around the web, linking the pages naturally. The link equity that passes from these sites to your site is the link juice, and this link juice differs in its authority depending on the sites linking to you.
Suppose you have sites A and B. If all other ranking factors are constant and site A has one link while site B has no links, site A will rank higher in search results due to the link juice it receives from the external site linking to it. What happens if site B also gains one link? This depends on the amount of juice each link passes. Look at the diagram below. Site A receives links from four sites while B receives links from two sites. All the linking sites receive link juice from other sites too. Since A receives links from more sites, there is more link juice being transferred to A and consequently A is likely to rank higher than B in search results. Note: These results assume the sites linking to A and B have a similar authority.
Another factor to consider is that passing link juice happens in both directions. So, now let us say that the sites linking to site A all also link to other sites too (represented by the grey arrows in the diagram below), whereas the sites linking to site B exclusively link to B. In this case the percentage of link juice that B receives is higher than the percentage of link juice site A receives. This increases site B’s chance at ranking higher than site A.
It used to be the case that the nofollow attribute could be used to preserve the loss of link juice. This process was known as PageRank sculpting. This was done to manipulate link juice such that its flow was concentrated on certain pages of a site rather than spreading evenly over all the pages. Refer to the diagrams below for a representation of this concept.
In the first diagram, you will see that with dofollow links (links that are not nofollowed) the transfer of link juice is equally distributed to all the outgoing links from a website.
PageRank sculpting was possible when a webmaster added a nofollow attribute to one of the outgoing links, which meant that the link juice would not transfer to the page that is nofollowed but would be distributed to the other links. This is demonstrated in the diagram below.
This is no longer true. Now link juice is passed the “normal” way no matter whether you use a nofollow or not. You can see in the next diagram that the site distributes its link juice to all three sites equally, the difference is that the nofollowed link does not receive it.
Since this is the case, you may be worried about the dilution or leaking of link juice from your home page to nofollow links on your footer or sidebar. A good and widely used practice is to stop the flow of link juice to spam comments and links posted on blogs with a nofollow attribute. On the contrary, when it comes to internal links on a site, it is a good practice to allow a natural flow of link juice rather than controlling it with nofollow attributes. The link juice obtained and distributed within your site keeps your inner pages popular on the web as well as your home page. This collectively enhances the PageRank of your home page.