Should you really merge multiple sites covering the same topic to boost your SEO?

Why is Google advocating for site consolidation?

The logic is straightforward: each site has its own authority capital, backlinks, and crawl history. When you fragment your content across three different domains that discuss the same topic, you dilute these signals instead of accumulating them.

Google evaluates the thematic relevance of a domain as a whole. A site that publishes 500 articles on digital marketing will be seen as more legitimate than a site that publishes 150, even if you have two other domains with 175 articles each on the same subject. The engine aggregates signals of semantic consistency, depth of treatment, and internal linking.

What does thematic centrality look like in practice?

The centrality is the ability of a domain to be identified as a reference on a given topic. Google creates a sort of semantic map: if all your content on technical SEO is on domaine-A.com, your strategic articles on domaine-B.com, and your case studies on domaine-C.com, the engine doesn't see three experts; it sees three moderately specialized sites.

Consolidating everything onto one domain allows for denser semantic networks, optimizing internal linking among all these contents, and maximizing internal PageRank. A technical article can point to a practical case, which itself links to a strategic guide. This flow of authority is impossible when you partition across multiple domains.

Does this recommendation apply in every case?

No. Google speaks of sites targeting “similar” subjects, not identical ones. If you have a B2C e-commerce site and a B2B media site in the same vertical but with radically different audiences and search intents, merging may create confusion.

The central question is one of user intent. If your sites meet distinct needs with different tones, formats, or journeys, keeping them separate may be justified. But if it's just an artificial segmentation to “cast a wide net” in the SERPs, Google clearly states that this strategy is no longer effective.

• Consolidation = accumulation of authority: backlinks, history, and relevance signals add up instead of fragmenting
• Optimized internal linking: circulation of PageRank among all contents within the same domain
• Strengthened thematic relevance: Google more easily identifies a site as a reference on a specific topic
• Exception for distinct audiences: if user intents are truly different, multiple sites may remain justified
• Beware of migrations: poorly executed consolidation can lead to significant temporary traffic losses

Does this statement align with field observations?

Yes, but with major nuances. On paper, the logic of concentration of authority is solid and confirmed by many successful migration cases. Sites that have merged two or three thematically related domains often observe traffic gains of 30 to 60% after stabilization. The consolidated PageRank, strengthened internal linking, and increased thematic depth are effective.

However, Google does not discuss the colossal risks of a poorly executed migration. A massive 301 redirect is a complex technical undertaking: loss of backlinks if redirects are poorly configured, a temporary ranking drop during Google’s reassessment phase, and cannibalization risks if similar contents are not properly merged. [To be verified]: Google provides no metrics on the failure rate of consolidations or the average recovery time for traffic.

In what cases does this rule not truly apply?

When sites have differing business models or distinctly different audiences. A concrete example: you have a high-traffic media site (advertising model) and a SaaS site with optimized landing pages for conversion. Merging them could muddle ranking signals and degrade the user experience. Google doesn’t make this distinction in its statement.

Another case: sites with very different backlink profiles. If domaine-A has a clean profile and domaine-B has received dubious links, merging may contaminate the former with potential penalties from the latter. Google never mentions this risk, even though it is very real. Before any consolidation, a backlink toxicity audit is essential.

What strategy should be adopted in response to this recommendation?

Do not rush in headfirst. Consolidation is a powerful but irreversible lever. If you're unsure, start with a test: identify the weakest site in your portfolio and migrate it to the strongest. Measure the impact over 6 months before extending the strategy.

Let’s be honest: many SEO professionals maintain multiple sites out of pure fear of losing acquired positions. This inertia has an opportunity cost. If your sites truly overlap, you are likely leaving 40 to 50% of traffic potential on the table. But the reverse is also true: a hasty merger without a solid migration plan can destroy years of work in just a few weeks.

What practical steps should be taken before merging multiple sites?

First, audit the SEO value of each domain. Use Ahrefs or SEMrush to compare Domain Rating, the number of referring domains, estimated organic traffic, and the distribution of positions. Clearly identify which site should become the primary domain: typically, it’s the one with the strongest backlink profile and the oldest history.

Next, map the contents. You will likely have duplicates or overlapping articles. Decide for each pair: merge with enrichment, canonical to the strongest version, or a hard redirect if one of the two doesn’t add value. This phase is lengthy but critical. A 301 redirect to irrelevant content destroys the value of the backlink and confuses Google.

What technical errors should absolutely be avoided?

NEVER mass redirect to the homepage of the primary site. This is the classic mistake that destroys 80% of SEO value. Each URL must be redirected to its closest thematic equivalent. If you don't have an equivalent, create one before the migration or redirect to a relevant category page.

Also beware of chained redirects. If domaine-B.com/article redirects to domaine-A.com/article, which already has a historical redirect, Google will lose part of the signal. Clean all existing redirects before launching the consolidation. And test your redirects on a sample before switching the entire site.

How can success of the consolidation be measured?

Define your KPIs before starting: overall organic traffic, average positions on your strategic queries, crawl rates, and changes in the number of indexed pages. Expect a temporary drop in the first 2-3 weeks, this is normal. Google reevaluates your entire architecture.

The real indicator of success emerges after 6 months. If your consolidated organic traffic exceeds the sum of the separate traffics prior to migration, you have succeeded. If not after this period, you likely missed a critical step in the migration. These operations require sharp technical expertise and a rigorous methodology that few organizations have in-house. To secure this type of strategic project, working with an SEO agency specialized in complex migrations can make the difference between a successful consolidation and a disaster in visibility.

• Audit Domain Rating and backlink profiles of each site to be merged
• Identify the primary domain with the strongest authority and history
• Map all contents and decide on mergers, canonicals, or redirects
• Configure individual 301 redirects to precise thematic equivalents
• Check for any chained redirects and clean existing ones
• Monitor traffic, positions, and indexing for at least 6 months post-migration