What Is Domain Authority? How the Third-Party SEO Metric Works
Domain Authority (DA) is a score from 1 to 100 that Moz, the SEO software company, assigns to a website to estimate how well it is likely to rank compared with other sites. It is built mainly from the site’s backlinks as Moz’s own crawler sees them. It is a third-party metric: Google does not calculate it and does not use it. Moz’s own Domain Authority page says so directly: “Domain Authority is not a Google ranking factor and has no effect on the SERPs.”
How Moz Calculates It
Moz states that it “calculates Domain Authority using a machine learning algorithm that evaluates multiple factors, primarily focusing on backlink data.” It continues: “These factors include the number of linking root domains, the quality of those links, and other signals that correlate with rankings across thousands of search results.” Moz describes the output as a score “from 1 to 100, with higher scores indicating a greater ability to rank.”
Three properties follow from how it is built:
- It is relative. Moz describes DA as “a relative measure rather than an absolute ranking factor,” so a score can move when competitors’ scores or the model change, even if nothing changed on your site.
- It is domain-level. It says nothing about which individual pages are strong; Moz’s Page Authority is the page-level counterpart.
- It depends on one company’s crawl. Links Moz has not discovered do not count toward the score.
Why It Correlates With Rankings Without Causing Them
Moz builds DA from link data and “other signals that correlate with rankings,” so a high score and good rankings can appear together. Correlation is the design of the metric, not evidence that the score causes anything. The score itself is not something Google reads. Google’s guidance on third-party SEO tools states that such tools “don’t have access to our internal ranking data.” Raising the number on a dashboard does nothing on its own; the links and content the number tries to reflect are what matter.
Domain Authority, Domain Rating, and Authority Score
Ahrefs and Semrush publish their own site-level scores. They look alike and are calculated differently, from different link indexes.
| Metric | Vendor | Scale | What the vendor says it measures |
|---|---|---|---|
| Domain Authority | Moz | 1 to 100 | Ability to rank, mainly from backlink data such as linking root domains and link quality |
| Domain Rating | Ahrefs | 0 to 100, logarithmic | The strength of a site's backlink profile |
| Authority Score | Semrush | 1 to 100 | A compound grade of a site's overall quality, calculated from eight weighted factors |
Sources for the rows: Moz’s Domain Authority page, Ahrefs’ Domain Rating glossary entry, which describes DR as “the strength of the website’s backlink profile on a logarithmic scale from 0 to 100,” and Semrush’s Authority Score article, which calls it “our compound metric that grades the overall quality of a website or a webpage.”
The same site will show three different numbers in the three tools, and none of them is the true one. Compare scores only within one tool.
What DA Is Useful For
- Comparing your link profile with a few direct competitors in the same tool.
- Triage of a long list of link or partnership prospects, before you look at each site’s relevance and real audience.
- Watching your own trend over months, next to referring domains, organic traffic, and rankings.
What it should not be is a goal. “Get our DA to 50” points effort at the score instead of at the links and content the score is meant to reflect.
How DA Can Be Inflated
Because DA is built from links, it can be pushed up with links that do nothing for search: networks of sites built to link, bulk paid links, or directory spam. Google’s spam policies count buying or selling links for ranking as link spam, and Google’s systems weigh relevance and spam signals that a third-party link count does not capture. A score inflated this way can also fall when Moz’s index drops those links or the linking sites lose standing in it, since Moz ties score changes to changes in a site’s backlink profile (see the last question below).
Questions About Domain Authority
What is a good Domain Authority?
It depends on the sites you compete with. Because the score is relative, a DA that leads a local niche can trail far behind in a national one. Compare against the sites ranking for your target searches, in the same tool.
Why did my DA change when I didn’t build or lose links?
Moz says a score “can increase or decrease based on factors like shifts in your backlink profile, changes in competitors’ scores, or updates to the DA calculation model.” Only the first of those depends on you.