SEO/link-juice implications of 'www.' links versus links without 'www.'

Question

I remember reading ages ago that it's a good idea to choose either www.example.com or domainexamplecom as your main URL and then set the other one as a 301 redirect to point to your domain?

The reason provided was:

1. Some people may link to www.example.com
2. Other links may point to example.com

In order to not lose 'SEO link juice', the individual recommended setting up a 301 redirect from one to the other.

Has this changed? Is it true? I would have guessed that Google (and other search engines) would be smart enough to whack some code in their algorithm to understand that in most cases www.example.com = example.com?

Answer 1

Yes it is true and no it hasn't changed. You should set a redirect from one to the other, or use the canonical tag to reference the canonical URL. (on this page they use an example of a URL with and without www).

As you mention Google is pretty smart and is usually quite good at figuring this out, but I often still see Google indexing both versions of URLs (with and without www prefix) when they are clearly the same page.

So you shouldn't leave it to chance and you should always make it clear which are your canonical URLs.

Answer 2

The main reason to redirect no-www to www (or the contrary) is to avoid duplicate content issues and not to avoid losing link juice. If you don't apply a 301 redirect, Google is going to index both versions of your website and will identify duplicate content (bad for SEO for sure).

Moreover, you can choose 301 redirect instead of rel="canonical" to avoid to lose link juice but just few of webmasters or users will be wrong on putting your URL on their websites.