Using WDF*IDF for SEO

WDF*IDF is a useful tool for SEO. It helps you understand what words are important in your texts and how to match them to what is happening in your industry online. In this article, I’ll show you how I use this formula to determine (in part) the quality of a text.

What is WDF*IDF?

WDF*IDF is a statistical measure used to assess the importance of a word within a document in relation to a collection of documents or a corpus. The formula helps identify the relevance of terms in a specific document while taking into account their generality in other documents.

This approach goes beyond the traditional model of keyword density and offers a more nuanced view of it. The main pitfall of keyword density is that it does not otherwise provide information around the distribution of a search term. WDF&IDF does.

The components explained:

  • WDF (within document frequency): This part of the formula evaluates how often a term appears in a document. It is similar to keyword density, but adapted to the length of the document.
  • IDF (inverse document frequency): IDF evaluates how common or rare a term is in all documents. A term that appears in many documents may be considered less significant.
Using WDF*IDF for SEO

The WDF*IDF Formula

The formula combines WDF and IDF to provide a score indicating the relevance of a term in a document, taking into account its frequency in other documents. This method helps identify terms that are unique and important to a specific document, which can lead to better SEO performance.

A real-life example

Suppose you have a document (let’s say, a blog post about “healthy eating”) and a collection of other documents (other blog posts about health and nutrition). You want to analyze the relevance of the term “organic” in your blog post.

  1. Calculate WDF (Within Document Frequency):
    • Suppose your blog post totals 1,000 words.
    • The term “organic” appears 10 times in your blog post.
    • So, the WDF for “organic” in your blog post is 10 / 1000 = 0.01 or 1%.
  2. Calculate IDF (Inverse Document Frequency):
    • Suppose there are 1,000 other blog posts in your collection of documents.
    • Of those 1,000 posts, 100 contain the term “organic.”
    • The IDF is then calculated as the logarithm of the total number of documents divided by the number of documents the term contains. Thus, IDF for “biological” = log(1000 / 100) = log(10) = 1.
  3. Calculate WDF*IDF:
    • The WDF*IDF score for “organic” in your blog post is then 0.01 * 1 = 0.01.

This score indicates how important the term “organic” is in your document compared to a larger collection of documents on a similar topic. A higher score means that the term is both relevant in your document and does not appear too often in other documents, indicating a good balance for SEO purposes.

It is important to remember that this is a simplified example. In practice, SEO specialists would use more sophisticated tools and methods to calculate and interpret WDF*IDF, especially when working with large data sets and complex content.

Application in SEO

WDF*IDF is used to analyze and optimize content for search engines. By identifying the terms that are relevant to a topic and not overused in competing content, SEO specialists can create content that is both unique and valuable to search engines.

Refining your content strategy

WDF*IDF can be used to refine content strategy. By analyzing which keywords have high relevance in your content relative to the overall frequency of usage in your niche, you can determine which keywords to emphasize or reduce. This helps create a balanced and effective keyword strategy that fits both your content and the broader market.

Competitive Analysis

An important aspect of SEO is understanding what your competitors are doing. WDF*IDF can be used to analyze competitor content. This allows you to identify what keywords they are using and how they contribute to their SEO success. These insights can be used to improve your own content strategy.

Content optimization

WDF*IDF helps optimize existing content. By analyzing the scores of your content, you can discover which keywords may be over- or under-represented. This provides an opportunity to customize content for better balance and relevance, which can lead to better rankings and user experience.

Identifying opportunities (within content)

WDF*IDF analysis can uncover opportunities – topics or keywords that are important to your niche but not yet adequately covered in your content. This provides opportunities for creating new, valuable content that can increase your visibility in search engines.

For many of my analyses, I use Ahrefs for this purpose. A short roadmap for this is.

  1. Look at the competition within Google (#1, #2 and #3).
  2. Look at all the search terms they come up for.
  3. Analyze what the distance is between the WDF*IDF and this search term.
Identifying opportunities

Improve quality of content

In addition to helping with content optimization, WDF*IDF can also improve the overall quality of content. By emphasizing terms that are truly relevant to the topic, content can become more informative and valuable to readers.

Usage combined with user intent

It is also important to combine WDF*IDF analyses with an understanding of user intent. Make sure keywords and content are not only optimized for search engines, but also aligned with what your target audience is looking for and expecting.

In short, WDF*IDF is a valuable tool for SEO specialists pursuing a sophisticated and data-driven approach to content optimization. By cleverly applying this technique, SEO professionals can improve the relevance and effectiveness of their content, ultimately leading to better search engine rankings and a stronger online presence.


In summary, WDF*IDF is a smart way to boost your SEO strategy. It helps you target exactly the right keywords and ensures that your content is both unique and relevant. By using this properly, you can make your website rank better in search engines and stand out from the competition. Remember, it’s just one of many tools in your SEO toolbox, but a very useful one.

Senior SEO-specialist

Ralf van Veen

Senior SEO-specialist
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I have been working for 10 years as an independent SEO specialist for companies (in the Netherlands and abroad) that want to rank higher in Google in a sustainable manner. During this period I have consulted A-brands, set up large-scale international SEO campaigns and coached global development teams in the field of search engine optimization.

With this broad experience within SEO, I have developed the SEO course and helped hundreds of companies with improved findability in Google in a sustainable and transparent way. For this you can consult my portfolio, references and collaborations.

This article was originally published on 15 November 2023. The last update of this article was on 22 November 2023. The content of this page was written and approved by Ralf van Veen. Learn more about the creation of my articles in my editorial guidelines.