Moz vs SEMrush KD: Understanding Keyword Difficulty Variations

 

Moz vs. Semrush KD: Which Should You Trust?

If you’ve ever used an SEO tool, you’ve probably come across a metric called “Keyword Difficulty,” or KD. This score, usually a number from 0 to 100, predicts how hard it will be to rank on the first page of Google for a specific keyword. It’s a foundational metric for any content strategy, helping you decide which keywords are worth targeting and which are a long shot.

Two of the biggest names in the SEO world, Moz and Semrush, both offer a KD score. However, if you’ve ever compared the two, you might have noticed something puzzling: the KD scores for the same keyword are often different. A keyword might have a KD of 45 in Moz but a 60 in Semrush. This can be confusing. Which tool is right? Which one should you trust to build your SEO strategy?

This post will clear up the confusion. We'll explore why these variations exist, how each platform calculates its score, and what it all means for your keyword research process. By the end, you'll have a much clearer understanding of how to interpret and use KD scores from both Moz and Semrush effectively.

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Why Are Moz and Semrush KD Scores Different?

The core reason for the discrepancy is that there is no universal, industry-standard formula for calculating keyword difficulty. Each SEO tool develops its own proprietary algorithm. Think of it like two different chefs baking the same type of cake. They might start with similar core ingredients—flour, sugar, eggs—but use different quantities, add their own secret ingredients, and have unique baking methods. The result is two cakes that are similar but taste distinct.

In the world of SEO, the "ingredients" for a KD score are various ranking factors. Both Moz and Semrush analyze the top-ranking pages for a given keyword, but they look at different signals and weigh them differently.

Key factors that can cause variations include:

• Backlink Data: Both tools have massive, distinct databases of backlinks. Since they crawl the web independently, their link indexes will never be identical. One tool might see more referring domains for a top-ranking page than the other, influencing the score.
• Authority Metrics: Each platform uses its own authority score. Moz has Domain Authority (DA) and Page Authority (PA), while Semrush uses Authority Score (AS). These scores are calculated differently and contribute to the final KD calculation.
• On-Page Factors: While backlink data is the primary driver, other elements like content quality, keyword usage in titles, and site speed can be factored in, with each tool assigning different levels of importance.
• Algorithm Updates: Both companies regularly tweak their algorithms to better reflect Google's ranking signals. A change in one tool's formula can widen or narrow the gap between its score and a competitor's.

Because of these differences, it’s best to view KD scores not as absolute truths but as relative guides within the ecosystem of the tool you are using.

How Moz Calculates Keyword Difficulty

Moz was one of the pioneers of SEO software, and its Keyword Difficulty score has been a staple for marketers for years. Moz’s calculation focuses heavily on the authority of the pages ranking on the first page of the SERP (Search Engine Results Page).

Key Components of Moz's KD Score

1. Page Authority (PA) and Domain Authority (DA): This is the heart of Moz’s calculation. Moz analyzes the PA and DA of the top 10 organic results for a keyword. Pages with higher PA and domains with higher DA are considered more powerful and harder to outrank. A keyword whose SERP is filled with high-DA sites like Wikipedia, Forbes, or government domains will receive a very high KD score.
2. Link Profile Strength: Moz’s algorithm looks at the number and quality of backlinks pointing to the top-ranking pages. It doesn't just count the links; it evaluates their authority, creating a more nuanced view of the link profile's strength.
3. Click-Through Rate (CTR) Factors: Moz also incorporates an "Organic CTR" score into its Keyword Explorer tool. This metric estimates the percentage of clicks a keyword's organic results receive, taking into account SERP features like ads, featured snippets, and video carousels that might "steal" clicks. While not a direct part of the KD number, it provides crucial context for whether a keyword is worth pursuing.

Moz’s approach is heavily weighted toward link-based authority. The core question it tries to answer is: "How strong are the link profiles of the pages we need to beat?"

How Semrush Calculates Keyword Difficulty

Semrush is another industry giant, and its Keyword Difficulty metric is a central feature of its extensive toolkit. While also heavily reliant on backlink data, Semrush’s formula incorporates a slightly broader set of factors.

Key Components of Semrush's KD Score

1. Backlink Authority: Like Moz, Semrush's primary input is the backlink profile of the top-ranking domains. It analyzes the number of referring domains, the authority of those domains (using its proprietary Authority Score), and the overall quality of the links pointing to the top 10 pages.
2. Keyword-Specific Link Signals: Semrush looks at the number of referring domains pointing to the ranking URLs and domains. It also considers the ratio of dofollow to nofollow links, which can indicate the nature of a site's backlink profile.
3. SERP Features: Semrush's calculation takes into account the presence of SERP features like featured snippets, knowledge panels, and local packs. A high number of these features can make it harder to gain visibility, even if you rank on the first page, and this can influence the difficulty score.
4. Volatility and Updates: Semrush updates its KD database frequently to reflect changes in the SERPs. The percentage is calibrated based on the most difficult keywords in their database, ensuring the scale remains relevant.

Semrush’s methodology aims to answer: "What is the overall strength of the domains we are competing against, and how difficult will it be to acquire the backlinks needed to compete?"

Practical Advice: How to Use These Scores

So, which score is better? The answer is neither. Both are valuable tools that provide a helpful estimate of ranking difficulty. The key is to use them consistently and understand their context.

Here are some actionable tips for using Moz and Semrush KD scores in your strategy:

1. Pick One and Stick with It

The most important rule is consistency. If you use Moz’s KD of 40 as a benchmark for a "medium" difficulty keyword, don't compare it to a Semrush KD of 40. The numbers are not interchangeable. Choose one primary tool for your keyword research to maintain a consistent frame of reference. This allows you to develop an internal sense of what a "low," "medium," or "high" KD score means for your specific website and industry.

2. Use KD as a Filter, Not a Final Verdict

Keyword difficulty should be one of the first filters you apply during keyword research, not the only one. Use it to quickly sift through large lists of keywords and eliminate those that are clearly out of your league. For example, if your site has a Domain Authority of 20, targeting keywords with a KD of 80+ is likely a waste of resources. Focus your energy on keywords where you have a realistic chance of competing.

3. Always Analyze the SERP Manually

No metric can replace a manual review of the search results. After you’ve filtered your keyword list by KD, take the most promising candidates and Google them. Look at the top 10 results and ask yourself:

• What is the search intent? Is Google showing blog posts, product pages, videos, or news articles? Make sure you can create content that matches this intent.
• Who is ranking? Are the top spots dominated by huge brands (e.g., Amazon, New York Times) or are there smaller blogs and niche sites? The presence of smaller sites is a great sign.
• What is the quality of the content? Read the top-ranking articles. Can you create something significantly better—more comprehensive, better designed, or more up-to-date?

4. Consider Your Website's Authority

A "high" KD score is relative. For a brand new website with zero authority, a KD of 30 might be challenging. For an established brand like HubSpot, a KD of 70 might be perfectly attainable. Compare the keyword difficulty score to your own site's authority (DA for Moz, AS for Semrush). A good rule of thumb is to target keywords with a KD that is at or below your own authority score, especially when you are trying to build momentum.

A More Informed Keyword Strategy

Understanding the differences between Moz and Semrush’s Keyword Difficulty scores demystifies a common point of confusion for marketers. Instead of seeing the conflicting numbers as a problem, view them as different perspectives on the same landscape. Moz emphasizes the authority of ranking pages, while Semrush provides a broad view of domain strength and link acquisition difficulty.

Ultimately, keyword difficulty is just a guide. It points you in the right direction, but it doesn't walk the path for you. The most successful SEO strategies combine data from these powerful tools with manual SERP analysis and a deep understanding of their own website's strengths. By doing so, you can move beyond the numbers and make truly informed decisions that drive meaningful organic traffic.