“Organic traffic" that you see in Ahrefs is calculated based on the keywords that we see your website is ranking for and the search volume of these keywords.
It will be different from the traffic numbers in Google Analytics for a number of reasons:
1. Ahrefs doesn’t track ALL the keywords that a website is ranking for in organic search results. We track the most popular ones and that is about 120 Million keywords for US only. In reality there are billions of keywords, and it’s technically impossible to track all of them.
2. Search volume of keywords - we have an excellent model for calculating monthly search volume of keywords, that combines data from Google Adwords with clickstream data. This is the best way to calculate search volume of a keyword as of today, and yet even this model is not perfect. Which leads to certain discrepancies.
3. CTR model - based on the monthly search volume of a keyword and its position in the search results, we estimate how many clicks a target website will get. Only Google knows the real numbers of clicks, so what we have is estimate, based on studies and research of how people search. That adds yet another layer of discrepancy.
So because of these 3 factors the data that we have is just estimate, and can’t be treated as the actual search traffic data of a website.
Marketers use this data to compare websites with one another and to see the trend in organic traffic (if the website is growing or losing traffic).
But you get the most value from Ahrefs data when you look at the actual keywords that your competitor is ranking for and the pages that bring them the most traffic from search. This data is much more accurate than our “big picture“ traffic estimation.