Semrush is widely perceived as the strongest keyword research tool and the best SEO software solution. Thousands of users regard Semrush as great for competitive analysis, keyword research, content creation, and rank tracking, but many would still turn to competing tools for backlink analytics.

We’re constantly working on expanding our backlink database, so we decided to investigate the comparisons.

Having run numerous internal tests to decide on the strongest backlink checker on the market, we’re now ready to share our first study on quantitative analysis with you.

We embarked upon the ultimate study to pit Semrush’s backlink database against the competing suites, based on a random set of 10K domains and collected backlinks data from each of the following tools:

  • Semrush
  • Ahrefs
  • Moz
  • Majestic

Out of the 10K domains selected, 33% had fewer than 1,000 backlinks, 34% had between 1,000 and 100,000 backlinks, and 33% had over 100,000 backlinks. The data was collected in February 2021.

With this foundation, we compared link indexes across all four tools on the number of referring domains and backlinks to develop a clear understanding of database quality across the board. 

Each database is unique in its own way, of course, but for clarity and transparency, we reviewed the following indexes:

Semrush —  Fresh index

Ahrefs —  Live Links

Moz —  Moz’s link index

Majestic —  Fresh index

Database Size Comparison

To start off, we looked at the total number of backlinks and referring domains reflected within each tool. 

This approach helped us estimate the size of each tool’s database, which, in turn, will provide an indication of where you can find the most comprehensive information and robust insights for your own analyses.

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When it came to the largest number of reported backlinks, Semrush led the way. Moz offered 22% less backlink coverage for the same set of domains with Ahrefs and Majestic showed even lower numbers.

For the total number of referring domains counted, Moz effectively came out on top, but, as we will cover later, discrepancies in the data showed that the top-level figures couldn’t necessarily be taken for what they were and, as a result, should be investigated further when it comes to conducting your own analyses.

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Absolute numbers, of course, can only tell us so much. 

We wanted to gain a better understanding of the make-up of each database and assess each tool on the distribution of their backlink coverage, so we calculated a “win ratio” based on the number of times each tool returned the most backlinks. 

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Here, the clear winner was Semrush: we managed to find the highest number of backlinks for 39% of domains analyzed. Moz came in second with about 25% of cases.

We did the same comparison for the number of referring domains reported by each tool, too. 

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For referring domains, Moz found the most in 48% of cases, while Semrush came in second with 37% of cases. To understand what this meant, we needed to look at the quality picked up within each index.

We then looked at the qualitative features of each backlink database.

While bigger sites with huge monthly traffic volumes may be in a better position to analyze their backlink profiles, smaller sites with comparatively low levels of traffic often struggle to access relevant data, despite actually having at least one backlink.

To investigate this, we calculated how many sites had referring domains picked up by each tool so we could see how many might return no data (zero referring domains): 

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Tool

Sites that showed data

Sites that showed no data

Semrush

99.48%

0.52%

Ahrefs

99.14%

0.86%

Moz

99.03%

0.97%

Majestic

98.28%

1.72%

Semrush found at least one referring domain for 99.5% of all analyzed URLs — more than any other tool. Since we were comparing the same set of domains across the tools, this means that Ahrefs, Moz, and Majestic are missing more data than Semrush in their backlink analyses. 

Let's take a look at what this means for the quality of backlink insights in the market.

As we showed at the beginning of the study, Moz picked up the highest total number of referring domains, but there’s more to this data than the absolute numbers. 

Semrush keeps its backlink database up-to-date by removing backlinks that haven’t been detected in six months. Moz doesn’t show when a backlink was last seen, so we used the Moz API to uncover that info.

We took a random sample of 100 smaller domains (with the total of 3,500 backlinks reported) out of the initial set to get a closer look at Moz from a backlink freshness perspective.

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As it turned out, nearly half of these backlinks were older than six months. 

We spotted that Moz reported backlinks coming from obsolete websites, so we decided to dig deeper and found, for instance, that it still showed backlinks from domains like plus.google.com, which no longer exists, so the total number of legitimate inbound links was evidently skewed. 

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In some cases, links reported by Moz actually couldn’t be reached.

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This could explain the reason behind Moz’s high referring domain figures — old referring domains seem to remain in the database. 

An outdated backlink database can potentially hinder any off-page efforts and lead to false impressions of your SEO performance, which, of course, can lead to misinformed decisions.

Considering all the stats from this extensive backlink study, the superiority of Semrush’s backlink database is clear:

  • Semrush absolutely leads the way when it comes to backlink coverage;
  • Moz outperformed the rest of the tools in identifying referring domain quantity, but since we spotted some instances of outdated sites, the quality of the data is questionable;
  • Ahrefs, widely perceived to be the leader in the field, consistently demonstrated inferior backlink data compared to Semrush, whether we looked at quantity or quality; and
  • Be it backlink or referring domain coverage, or the number of missing data, Majestic consistently came in last compared to the other tools.

Many still view Ahrefs as their go-to platform for backlink analytics, so we decided to go a step further and put it to the task on social media. 

We often run quick backlink comparisons for our clients’ sites. Although it’s not a major study, these findings reflect the significant progress Semrush is making with its backlink coverage. 

To get a Semrush-Ahrefs backlink data comparison, we asked our clients to drop their domains for quick analysis within our Facebook group (if you’re not a member, you need to fill in the form to get in). 

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We took our index and compared it to Ahrefs’ Live index. We analyzed 39 domains, providing users with two screenshots that reflected stats within each tool based on referring domains and inbound links. Semrush won in 51.3% of cases (20 out of 39), outperforming Ahrefs, which won in only 12.8% of cases (5), in both depth and breadth of backlink analysis. It was a draw in the remaining 35.9% of cases (14); here you can find the detailed stats for all the domains that were analyzed. 

We then took the battle to Twitter. Overall, we had a total of 31 followers participate and submit their sites. Comparing both categories, Semrush won in over half of them (58.1%, 18 out of 31 domains).

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A draw occured in 32.3% of cases (10 out of 31), while Ahrefs only pulled ahead in both categories for three websites listed in our test, representing 9.7% of cases (3 out of 31).

For both comparisons, we matched our backlink database with Ahrefs’ Live Index (its default index when reviewing a domain). Even when recalculating the results comparing our index to Ahrefs’ Recent Index (which includes “live” links that were recently lost), Semrush pulled ahead in 39% of cases, while a draw occured 42% of the time (13 out of 31 domains), and Ahrefs won in 28% of cases. 

Check out the results for our Twitter battle with Semrush index vs Ahrefs’ Live and Recent indexes. 

As demonstrated in this study, in many cases, our data is already superior to what other providers have, which means our users can always expect to receive the largest and freshest sets of backlinks data to amplify their SEO performance.

With our expert engineering and product teams dedicated to enhancing our tools every day, we're continually building on our backlink analysis offering to ensure it’s the most comprehensive database out there for you to study and learn from your and your competitors’ backlink profiles. 

Check out the Backlink Analytics tool and learn more about it over on the Knowledge Base today. 

Author Photo
Olga AndrienkoTogether with her team she has built one of the strongest international communities in the online marketing industry. Olga has expanded Semrush brand visibility worldwide entering the markets of over 50 countries. In 2018 Olga was mentioned among the 25 most influential women in digital marketing by TopRank. She speaks at major marketing conferences and her quotes on user behavior appear in media such as Business Insider and Washington Post.
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