Keyword Difficulty
Keyword Difficulty is an SEO metric, scored from 0 to 100, that estimates how much competition you face to reach the first page of Google search results (the top 10) for a given keyword. Because Ahrefs, Semrush, Moz, and other tools each calculate it differently, treat it as a relative estimate rather than an absolute figure.
- Keyword difficulty is a metric that estimates, on a 0-100 (or 1-100) scale, how strong the competition is to rank highly for a given keyword.
- Most tools use the number of backlinks (referring domains) and the authority of the pages currently ranking in the top 10 as their core inputs.
- Scores differ by tool: Ahrefs is based on referring-domain count, Semrush on multiple factors (referring domains, authority score, SERP features), and Moz on page and domain authority.
- Scores are estimates rather than absolute values, so you should weigh them alongside your own site's authority and the keyword's search intent when selecting opportunities.
- The efficient strategy is to prioritize keywords that combine low difficulty with the right search volume and intent.
Overview
Keyword difficulty is a metric that estimates, on a 0-100 scale, how hard it is to break into the first page of Google search results (the top 10) for a particular keyword. A higher score means tougher competition and more effort required to rank near the top. In content strategy, it serves as a yardstick for deciding which keywords to pursue: rather than blindly chasing high-volume terms, you use it to surface keywords where the opportunity outweighs the difficulty.
The most important caveat is that keyword difficulty is an estimate calculated differently by each tool. Google does not publish this value officially; each SEO tool derives it with its own algorithm, so the same keyword can carry different scores in Ahrefs, Semrush, and Moz. For that reason, it is better used for relative comparison between keywords within a single tool than taken as an absolute number.
Scoring Factors
Most tools rely on the volume of backlinks (referring domains) and the domain authority of the pages currently ranking at the top for a keyword. The stronger those top pages are in backlinks and authority, the harder it is judged to be to displace them, and the higher the difficulty is set.
Differences by Tool
| Tool | Scale | Main Scoring Factors |
|---|---|---|
| Ahrefs (KD) | 0-100 (logarithmic scale) | Based solely on the number of referring domains (RD) to the top 10 pages. On-page factors are not included |
| Semrush (KD%) | 0-100 (%) | Multiple factors: median referring domains, dofollow/nofollow ratio, median authority score, SERP features, and more |
| Moz | 1-100 | Based on the page authority (PA) and domain authority (DA) of the top pages |
Ahrefs derives KD only from the referring-domain count of the top 10 pages and states explicitly that it does not factor in on-page SEO. Another characteristic is that the score is logarithmic rather than linear. According to the official Ahrefs blog, a KD of 0-5 means the top pages have almost no backlinks, around KD 50 means hundreds, and KD 90 or above means the pages competing have thousands of backlinks.
Semrush calculates KD% from multiple factors rather than a single input. It combines the median referring domains of the top URLs, the median ratio of dofollow to nofollow links, the median domain authority score, and keyword-level attributes such as search volume, word count, and SERP features, weighting each differently and then calibrating against the regional database. Semrush groups KD% into the following six bands.
| Semrush KD% Band | Difficulty |
|---|---|
| 0-14 | Very easy |
| 15-29 | Easy |
| 30-49 | Possible |
| 50-69 | Difficult |
| 70-84 | Hard |
| 85-100 | Very hard |
Moz, within its Keyword Explorer, analyzes the page authority and domain authority of the top 10 pages to assign a score from 1 to 100. The higher the average authority of those top pages, the higher the difficulty score climbs.
Application
The most practical use of keyword difficulty is selecting opportunity keywords. By finding keywords with ample search volume but low difficulty, that is, keywords whose top pages have weak backlinks and authority, you can secure visibility quickly with fewer resources. This is especially effective for new sites or low-authority domains, which benefit from avoiding high-difficulty keywords and building a foundation on low-difficulty long-tail terms first.
Rationale and Cautions
Ahrefs notes that while the KD score reflects SERP competition fairly accurately, you should not make every SEO decision on KD alone. Its reasons: (1) KD is an average difficulty, not a personalized difficulty that accounts for your own site's authority; (2) a high KD can mask opportunities such as stale content or low-authority competitors; (3) backlink quality matters more than quantity, so a raw count can be misleading; and (4) it cannot measure search intent. Ultimately, sound judgment requires looking at the actual search results yourself.
The differences between tools must also be kept in mind. Because Ahrefs weights only referring-domain count, Semrush weights multiple factors, and Moz weights page and domain authority, the same keyword can produce different scores. It is therefore safer to use the scores for setting relative priorities between keywords within one tool than to compare numbers across tools as absolutes.
Execution Checklist
- Use difficulty scores as a relative benchmark within the same tool, not as absolute values.
- Look at search volume, search intent, and difficulty together to select balanced opportunity keywords.
- For new or low-authority sites, prioritize low-difficulty long-tail keywords first.
- Even for high-difficulty terms, check the SERP directly to see whether the top pages include stale content or low-authority competitors.
- Evaluate backlinks by quality (authority and relevance), not just by count.
- Make decisions on the assumption that scores may differ across tools.