Duplicate Content:
Split Authority Is Diluted Authority.

Yes, though not in the way most people assume. Google doesn't penalize duplicate content with a manual action in most cases — instead, it filters it. When Google finds the same content at multiple URLs, it picks one version to index and suppresses the others. The problem is that the version Google chooses may not be the one you want to rank, and the backlink authority and crawl signals that should consolidate on your preferred URL get diluted across all versions. The result is weaker rankings across the board.

Duplicate content is any substantially similar or identical content that appears at more than one URL — on your own site or across different domains. Common examples include: the same page accessible at both HTTP and HTTPS versions, www and non-www variants, URLs with and without trailing slashes, product pages with URL parameters, paginated pages, printer-friendly versions of pages, and content syndicated to other websites. Near-duplicate content — pages that are mostly the same with only minor variations like a city name — also triggers duplicate content signals.

The fix depends on the cause. For URL variations (HTTP/HTTPS, www/non-www, trailing slashes): set up 301 redirects to your preferred version and add canonical tags. For pages with URL parameters: add canonical tags pointing to the clean URL, or configure parameter handling in Google Search Console. For paginated content: use canonical tags or rel=prev/next. For near-duplicate location or service pages: rewrite each page with unique, location-specific content. For externally syndicated content: require publishers to add a canonical tag pointing back to your original.

There's no precise percentage Google has published. In practice, pages that share more than roughly 50–60% of their content with another URL on your site risk being filtered from search results. Even lower levels of shared content become problematic when repeated across many pages — for example, ten location pages that are 30% identical collectively create a significant near-duplicate signal. The safest approach is to ensure every page you want to rank has a meaningful amount of unique, differentiated content relative to every other page on your site.

Google does not issue automatic penalties for honest duplicate content — it filters it rather than penalizing it. However, if Google determines you've intentionally created duplicate content to manipulate rankings (for example, scraping content from other sites at scale, or mass-producing near-identical pages with keyword stuffing), a manual action is possible. For the vast majority of small business sites, duplicate content is an unintentional technical issue that costs rankings through dilution, not through penalties.