Domain Authority is Moz's proprietary metric, calculated through a machine learning algorithm that processes over 40 variables in their link index. The score runs from 1 to 100 and predicts how well a domain might rank in search results relative to competitors. The core inputs include the number of linking root domains (most important), total backlinks, MozRank (link equity distribution), MozTrust (proximity to trusted seed sites like universities or government domains), and various quality signals about those links. The calculation is logarithmic, meaning jumping from DA 20 to 30 is far easier than moving from 70 to 80. A site with 100 quality backlinks from diverse domains might hit DA 25-35, while breaking past DA 60 typically requires thousands of referring domains and strong link profiles. Moz recalculates DA roughly monthly as their index updates, so your score can fluctuate even if you haven't built new links, simply because competitors did or Moz's model changed. Critically, DA is not a Google ranking factor. Google doesn't use it, doesn't see it, and has its own internal authority metrics we can't directly measure. DA is useful as a comparative benchmark when evaluating link prospects or tracking progress against competitors in the same niche. At Ottawa SEO, we treat DA as one data point among many. A DA 45 site in a relevant niche with engaged traffic often delivers more value than a DA 60 generic directory. Similar metrics exist from other providers: Ahrefs uses Domain Rating (DR), Semrush has Authority Score, and Majestic offers Trust Flow and Citation Flow. Each uses different crawl data and algorithms, so the same site might be DA 52, DR 48, and Authority Score 39. None are perfect proxies for Google's view, but they're directionally useful for link prospecting and portfolio health checks. Focus on the trend over time and relative standing in your niche rather than obsessing over the absolute number.