This article will guide you through the main reasons why pages get listed on this index, and most importantly, how to get them out. If you have an existing site, there is a high probability that you may have pages in the supplemental index, so use this as a reference, and make sure you follow the steps outlined here.

First of all, for those of you new to this topic.
What is the Supplemental Index? Here is the short answer… Google has actually 2 indexes, on call the “Main Index” and a secondary one known as “Supplemental”. One way to verify that you are looking at a supplemental result is that you can see “Supplemental Result” in green text on the bottom line of any given Google listing.

Why do pages move from main to supplemental?
There are many obvious, and some not too obvious reasons for this, but Duplicate Content and Non-Updated are the two main ones. A “too dynamic” url, in other words, with too many variables, or a page that is to deep in the site’s structure also accounts for this. A word of advice on linking: If you are doing excessive reciprocal links, link buying/selling or linking to spammy neighborhoods… stop! Google algorithms has very low trust in the inbound and outbound links of those sites.

Solutions to get out of the supplemental index.
Now that you know what this index is and why you don’t your pages in it, I will go over ways you can get them out, and back to were they belong, the main index. I will group them in pairs as they are co-related:
1. Duplicate Content and Content Quality. All your meta tags should be unique. All pages have common elements like navigation, footer, etc. Make sure your page have enough unique content to offset these elements, and that you are providing quality with as well.
2. Dynamic URLs and Site Structure. Keep all URLs as “static” as possible. Why passing 3-4 variables if there is a simpler way? And every page should be 2-3 clicks away from the home page, as far as the site structure. Please refer to Google Best SEO Practices – Part 4.
3. Your Internal Linking and Profile. Your sitemap, which is very important component of your internal linking, should include links to all the pages on your site, and it should be linked (normally in the footer) from every page. And your site’s overall link profile directly impacts the level of trust Google gives it, and since this affects the PageTrust, less trust often translates into more supplemental pages.

Again, like I said before, make it easy on Google, and they will make it easy on you

By Dedicated SEO Consultant: Jose Nunez