50% Error Gap: Checking 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?

Which service do you deploy to estimate traffic…

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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 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. The dashboard now estimates 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 and simple: they take search queries, demand for these queries, and apply their unique CTR calculations. The service provides fairly accurate results, though they hugely depend on the site 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 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 traffic analysis is grounded 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. 

The service shows organic traffic quite well, but it provides inaccurate data for websites with low traffic, which is one of the main disadvantages

The hidden calculation system 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 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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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 jumps 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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