Domain Authority is owned and calculated exclusively by Moz, the SEO software company. They built DA as a predictive metric (scored 1–100) that estimates how well a domain might rank in search results based on backlink profile strength, using their own web index and machine learning models. Moz updates the scores regularly as their index grows and their algorithm changes, which means your DA can fluctuate even if your actual link profile stays identical. Google does not use Domain Authority in its ranking algorithm and never has. Google engineers have stated this repeatedly. Instead, Google relies on its own proprietary authority signals—things like PageRank derivatives, E-E-A-T assessments, link quality evaluations, and topical relevance factors that are far more sophisticated than any single numeric score. When Google's John Mueller says "we don't use Domain Authority," he means it literally. Other SEO platforms have their own competing metrics: Ahrefs uses Domain Rating (DR), Semrush has Authority Score, and Majestic offers Trust Flow and Citation Flow. Each uses different crawl data, different link weighting, and different formulas, so a domain might score 45 DA on Moz but 60 DR on Ahrefs. None of these tools can perfectly reverse-engineer Google's actual authority calculations because they don't have access to Google's full index, user behavior data, or ranking signals. At Ottawa SEO, we track DA and DR as reference points when evaluating link prospects or monitoring portfolio health across our 500+ domains, but we never optimize for the scores themselves. A site can have DA 30 and outrank a DA 60 competitor if it has better content relevance, user engagement, and contextual authority in its niche. We focus on acquiring links that move actual organic traffic and rankings—metrics Google does care about—rather than chasing third-party scores that shift whenever Moz or Ahrefs recalibrates their models. If your DA drops after an index update but your traffic holds or grows, you're fine.