In general, subdomains are not ranked separately from their domains. The only major exception to this is the case of blogs or personal pages that are hosted on a recognized blog/host site. For example, blogs on blogspot.com or livejournal.com will usually have their own Traffic Ranks, provided we have sufficient data for them.
We do show a breakdown of visitors by subdomain in the "Where do visitors go on X" section of a site’s Site Overview page.
Not all subdomains of a site might be listed in the "Where do visitors go" section. If we have not seen measurable traffic to a subdomain from our traffic panel, it will not appear on the list. Also the list of subdomains may change over time, as more or less data is available. Even if a particular subdomain is not listed in the "Where do visitors go on X" list, traffic to that subdomain is still counted as part of your site’s traffic.
We update the "Where do visitors go" data monthly for all sites. The data is based on the trailing month.
Note: Sites with Certified metrics can elect to show directly measured "Where do visitors go" information.