Keyword density is the percentage of times a target keyword appears in a piece of content relative to its total word count. It was prominent in early SEO practice — circa 1997–2010 — when search engines relied heavily on term frequency to determine a page's relevance. A page discussing web hosting that used the phrase "web hosting" in 2% of its words would be judged more relevant than one using it in 0.2% of words.
Keyword density is not a modern ranking factor. Google's algorithms have moved well past raw frequency counting toward semantic understanding: they evaluate whether a page thoroughly covers the concepts, entities, and related topics associated with a query — not whether a specific string appears at a set percentage. There is no documented optimal density figure, and chasing one produces content that reads unnaturally for human visitors without delivering SEO benefit.
Where density thinking causes active harm is when it leads to keyword stuffing — forcing the target phrase into every heading, sentence, and image caption regardless of whether it fits. Google's spam policies explicitly identify keyword stuffing as a violation. The correct frame in 2026 is intent coverage: a well-written, thorough page that naturally discusses its topic will use the primary keyword and its semantic variants frequently simply because the topic warrants it — not because a formula was applied.