Developed by the SEO software company Moz, domain authority is a search engine ranking score that predicts a website’s ability to rank on search engine results pages or SERPs. Domain authority ranges from a score of 1 to 100. The higher your score, the better your website will rank.
To calculate websites’ domain authority, Moz accounts for over 40 factors, like root domains and total number of inbound links. Websites with a large amount of high-quality inbound links, like Wikipedia, have the highest domain authority. New websites with little to no inbound links typically have a domain authority of one.
Moz’s domain authority scale is also logarithmic, which means when your domain authority is higher, it’s harder to improve your authority score. For instance, increasing your domain authority from 70 to 80 is more challenging than increasing your domain authority from 20 to 30.
Additionally, your website’s domain authority can decrease, even if you don't lose any backlinks, when a high-authority website, like Facebook, receives an influx of backlinks.
Since Moz can’t give the highest-authority websites a domain authority score over 100, they keep their score at 100 while lowering other sites’ domain authority. In other words, your website’s domain authority is relative to the domain authority of the highest authority website.
Information on this subject was gathered by Hubspot.