Comparing Traffic Data Accuracy: Similarweb vs. Ahrefs vs. Semrush

Interestingly, there are data gaps provided even by the best SEO tools like Similarweb, Ahrefs, and Semrush among others. Our analysis shows that no single service is perfect. Our findings provide valuable insights that will help you check website traffic more accurately.
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50% Error Gap. Revealing Data Accuracy Delivered by Similarweb, Ahrefs, and Semrush

Why Google Search Console, when Ahrefs denies the data? 

Similarweb shows completely different data. Where’s the correct data? Is Similarweb accurate? Which is better Ahrefs vs Semrush?

You must have coped with these burning questions in your digital marketing practice. Everyone knows that Ahrefs Similarweb, and Semrush data assume certain deviations in traffic forecasting. But what are the actual errors? The thing is that these services do not fully disclose their methodologies, so we explored and analyzed major indicators compared to real figures.

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How We Approached the Issue?

To come up with accurate calculations, we collected 184 websites with different traffic volumes. The smallest resource in our analysis received about 5,000 views per month, while the largest one - above 8,000,0000 respectively. 

We took data from these sites from Google Search Console for the first six months of 2024. Next, we took information for the same period from the acknowledged SEO search tools Ahrefs Similarweb, and Semrush, and compared the indicators. The approach enabled us to identify an average error percentage for each service and its pros and cons.

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Data Analysis by Similarweb

Similarweb deploys four data sources to estimate organic and other traffic channels:

🔴 Direct estimates: data from sites that enable Similarweb internal tracking systems.

🔴 Contributor network: donations of certain consumer products that help analyze user behavior anonymously. 

🔴 Partnerships: a global network of organizations that collect digital signals on the web and pass them on to Similarweb for further analysis and use. 

🔴 Public data extraction: a proprietary algorithm that collects information from many websites.

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The greatest Similarweb advantage is the update since July 2024. They improved their tracking system, which has substantially increased the number of sites where the indicators differ from the actual ones with a minimum error percentage. We consider Similarweb to have the largest potential for further development and improvement.

Similarweb claims they have included additional parameters to account for seasonal traffic changes. That is the peculiarity of this website traffic checker. The dashboard now estimates website traffic coming from mobile devices.

‍Service upsides:

• Access to the data from all traffic types, including referral and paid traffic
• Convenient reviews and competitor comparisons
• Quite high accuracy after the update on 28.07.2024.

‍Service downsides: 

• Inaccurate data for websites with low traffic (<5000).
• The traffic calculation system depends on the availability of a large amount of data.

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Data Analysis by Ahrefs

Ahrefs’ methodology for data evaluation is consistent, while its understanding is simple: they take search queries, demand for these queries, and apply their unique CTR calculations. The service audit provides fairly accurate results, though they hugely depend on the site ranking positions to estimate traffic. If the data on positions is updated quickly, Ahrefs shows the traffic volume better, though once the data is outdated, the traffic estimate will be irrelevant.

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Ahrefs performance accuracy dashboard does not have a monthly traffic total for each site. Ahrefs has developed a daily measurement model that shows the approximate monthly traffic based on its current vision for certain search queries. With that, the service has quite a few points that can affect the growth of the error rate. 

‍Service upsides:

• The traffic calculation is transparent and comprehensive
• The system deploys various sources to update the frequency and request dynamics.

‍Service downsides:

• Delay in updating positions = data errors 
• It is unclear how CTR is calculated
• Keyword positions have changed = monthly traffic estimate has changed. There is no final calculation of traffic for the month.

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Data Analysis by Semrush

Semrush website traffic analysis grounds on petabytes of click data from both its own and third-party sources. The service does not disclose which third-party sources it uses. Semrush uses an internal model to estimate the total traffic volume. 

Semrush SEO tools show organic traffic quite well, but it provides inaccurate data for websites with low traffic, which is one of the main disadvantages

Semrush website analytics assumes a hidden calculation system that does not allow for a deeper analysis of Semrush's approach to assessing the situation. The panel provides estimated traffic data, not actual data. This means that there will always be a certain error in their data.

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Service upsides:

• Semrush analytics is based on keyword positions and estimated traffic: search volume multiplied by average CTR).

‍Service downsides: 

• Inaccurate data for websites with low traffic
• Hidden calculation system
• Traffic data is estimated, not actual.

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👉 Takeaway: All three tools require investment, but none of them provide 100% accurate traffic numbers. The smartest approach is to cross-check data across multiple platforms and validate it against Google Search Console to minimize the average 50% error gap.

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How Semrush Calculates Traffic Data

Semrush bases its traffic estimates on massive amounts of clickstream data—billions of signals collected from both its own and undisclosed third-party sources. This data is then run through Semrush’s internal models, which predict the total number of visits a site may be getting. In practice, this means that Semrush is strong when it comes to showing organic traffic trends and keyword-driven insights.

However, because its methodology isn’t transparent, marketers often face discrepancies between Semrush numbers and real Google Search Console data. The estimates also tend to be less reliable for smaller websites with low traffic volumes, where the error rate can be quite high.

How Similarweb Calculates Traffic Data

Once, we've determined how accurate is Similarweb, let's view how Similarweb calculates traffic. Similarweb stands out by combining several data sources into one system. It gathers information through direct measurement (websites that allow tracking), its contributor network (apps and tools that share anonymous behavioral data), partnerships with global organizations, and public data extraction via proprietary algorithms.

Since the July 2024 update, Similarweb has significantly improved accuracy, especially for mobile traffic and seasonal trends. The platform also gives a broader view of all traffic types, including referrals, paid campaigns, and competitor benchmarking—something other tools don’t always provide. Still, Similarweb struggles with small websites under 5,000 visits/month, where there isn’t enough data to build reliable models.

How Ahrefs Calculates Traffic Data

Ahrefs takes a different route by focusing on search demand and rankings. The tool estimates website traffic by analyzing keywords a site ranks for, their search volumes, and an internal CTR (click-through rate) model. This makes Ahrefs particularly useful for measuring SEO performance and keyword potential.

However, there are a few limitations. Because Ahrefs recalculates traffic estimates daily, any delay in keyword position updates can lead to outdated or misleading results. Moreover, Ahrefs doesn’t provide a final monthly traffic total—instead, it shows evolving estimates based on current rankings. While this approach is transparent and easy to understand, it can create confusion when keyword positions fluctuate.

Pricing

• Semrush: Starts at around $129.95/month, offering a wide suite of SEO, PPC, and competitive analysis features. Best suited for agencies or businesses that need an all-in-one toolkit.
• Similarweb: Offers a free version with limited insights, while enterprise packages with advanced competitor and traffic data can go well into the thousands per month depending on scope. It’s often a better fit for companies focused on market intelligence.
• Ahrefs: Pricing begins at about $99/month, with strong emphasis on backlink data, keyword tracking, and SEO audits. It’s popular among SEO specialists who want transparent keyword-driven metrics without paying for a full marketing suite.

Takeaway: All three tools require investment, but none of them provide 100% accurate traffic numbers. The smartest approach is to cross-check data across multiple platforms and validate it against Google Search Console to minimize the average 50% error gap.
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Similarweb vs Ahrefs vs Semrush: Conclusions Backed up by Numbers

Synthetic data from the analyzed services has an error that should be considered in the planning process. This is due to their data calculation methodologies. 

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The average error rate for all services (Ahrefs, Similarweb, Semrush) is 50%.

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This is less than we expected when we launched our research: during the analysis, we spotted many cases with abnormal shifts on some sites. Eventually, we failed to track any correlation: these were different resources considering traffic and niches.

The major takeaway is to look at indicators and check data across these services to mitigate the likelihood of high error anomalies. 

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