Domain Authority is a proprietary score from Moz that runs 0–100, predicting how well a domain should rank in search results. It's calculated using a machine-learning model trained on actual Google rankings, factoring in total backlinks, linking root domains, domain age, link quality signals (MozRank and MozTrust), and spam indicators. The scale is logarithmic, so jumping from 20 to 30 is easier than 70 to 80. Moz updates DA periodically when they refresh their link index, which means scores can shift even if you haven't changed anything—competitors gaining links can lower your relative DA. Other tools have similar metrics: Ahrefs calls it Domain Rating (DR), Semrush uses Authority Score, and Majestic offers Trust Flow and Citation Flow. Each uses different crawl data and algorithms, so a site might score DA 45, DR 52, and Authority Score 38 simultaneously. Google does not use DA, DR, or any third-party authority score in its algorithm. These are correlative proxies—sites with strong link profiles tend to rank well and score high on DA, but the score itself doesn't cause rankings. We've seen DA 25 local service sites in Ottawa outrank DA 60 national directories for geo-specific queries because of relevance, user signals, and targeted local links. At Ottawa SEO, we track DA/DR as one indicator in our 500+ domain portfolio, but we prioritize referring domains from relevant, non-spammy sources over chasing a number. A single contextual link from a DA 70 industry publication often moves the needle more than ten DA 30 blog comments. When auditing a potential link opportunity, check the domain's actual organic traffic (Ahrefs or Semrush estimates), topical relevance, and whether it passes manual review—does it look like a real site humans use? DA is a shortcut for those checks, not a replacement. If you're buying expired domains or evaluating partnership sites, cross-reference DA with traffic trends and link velocity to avoid metric-manipulated shells. How Moz Calculates DA Using Machine Learning Moz calculates DA through a machine-learning model that reverse-engineers ranking patterns from millions of SERPs. The model identifies which link characteristics correlate most strongly with top positions, then weights those factors accordingly. When Moz retrains this model—which happens during major algorithm updates—DA scores across the web can shift even without any link changes on your end. The model pulls from Moz's Link Explorer index, which crawls and processes link data continuously. Understanding how Moz calculates DA helps contextualize score changes: a drop might reflect model recalibration rather than lost links. You can verify this by checking Moz's changelog for recent updates before assuming something went wrong with your link profile. Domain Authority Measurement Criteria Breakdown Domain authority measurement criteria extend beyond raw link counts into qualitative factors Moz's algorithm weighs differently. Linking root domains matter more than total backlinks—fifty links from one site count less than fifty links from fifty different domains. Link freshness plays a role: recently acquired links from active sites carry more weight than stale links from dormant domains. The algorithm also evaluates the authority of linking pages themselves, creating a recursive quality assessment. Spam signals act as negative factors: excessive exact-match anchor text, links from known link networks, or sudden unnatural link velocity can suppress scores. Moz's spam score metric, visible in Link Explorer, directly influences DA calculations when it flags problematic patterns in your backlink profile. What Factors Affect Domain Authority Over Time Several factors affect domain authority independently of your own link building efforts. Competitor link acquisition is the most overlooked: because DA is relative, other sites in Moz's index gaining links can push your score down even if your profile stays static. Index expansion matters too—when Moz discovers previously uncrawled linking domains pointing to your site, scores can jump unexpectedly. Losing high-authority referring domains through site closures or link removals creates measurable drops. Internal factors include site structure issues that prevent Moz's crawler from discovering all inbound links, and subdomain versus root domain configuration affecting how link equity consolidates. Monitoring DA monthly alongside referring domain counts in Link Explorer helps distinguish real profile changes from algorithmic noise. Practical Limitations of Domain Authority as a Metric DA works best as a quick filtering tool rather than a performance target. The score updates on Moz's crawl schedule, not in real-time, so recent link wins might not reflect for weeks. Niche sites often plateau at moderate DA levels simply because their industries lack high-authority linking opportunities—a DA 35 legal blog in a specialized practice area can significantly outperform a DA 55 general business directory for relevant queries. Gaming DA through private blog networks or link schemes typically produces short-term score inflation followed by corrections once Moz's spam detection catches up. For client reporting, we recommend tracking DA alongside referring domain growth, organic traffic trends, and actual keyword rankings to give a complete picture rather than fixating on a single number. Frequently Asked Questions How is domain authority calculated? Domain authority is calculated using Moz's machine-learning model that analyzes linking root domains, total backlinks, link quality signals like MozRank and MozTrust, spam indicators, and domain age. The model trains on actual SERP data to predict ranking potential on a logarithmic 0–100 scale. What factors affect domain authority? Factors affecting domain authority include number of unique linking root domains, quality and authority of those linking sites, spam signals in your backlink profile, competitor link acquisition rates, and Moz's index updates. Link diversity and freshness also influence scores. How does Moz calculate DA scores? Moz calculates DA by running backlink data through a machine-learning algorithm trained on millions of search results. The model identifies which link characteristics correlate with high rankings, weights those factors, and outputs a score that gets recalibrated when Moz retrains the model. What are domain authority measurement criteria? Domain authority measurement criteria include linking root domain count, total backlink volume, link source authority, anchor text patterns, spam score signals, link freshness, and domain age. Moz weighs these factors using a proprietary algorithm updated periodically with their link index refreshes.