Keyword difficulty (KD) is a score, usually from 0 to 100, that SEO tools assign to a keyword to estimate how hard it would be to reach the first page of Google. It is a quick filter during keyword research, but it is only an estimate and should never be the only factor in your decision.
How tools calculate it
Each tool uses its own formula:
- Ahrefs bases KD mainly on how many referring domains the top ten pages have.
- Semrush combines links, authority scores and SERP features.
- Moz uses the page and domain strength of ranking pages.
Because the inputs differ, the same keyword can score 20 in one tool and 55 in another. Compare keywords within one tool rather than across tools.
What the scores miss
- Content quality: weak, outdated pages ranking on page one are an opportunity no score shows.
- Intent match: you may not be able to rank a product page for a query Google treats as informational.
- Your own strength: difficulty is relative. A keyword that is hard for a new site may be easy for an established niche authority.
- SERP features: AI Overviews, maps and ads can make a low-difficulty keyword low-value too.
A practical way to assess difficulty
- Search the keyword in an incognito window from your target country.
- Check what type of page ranks and whether you can produce that type. See search intent.
- Look for weak spots: forum threads, thin pages, outdated posts, small sites.
- Note the domain authority and referring domains of the top results, compared with yours.
- Count the SERP features that push organic results down.
- Decide: can you build something clearly better, and earn the links it needs?
Rough guide by site strength
- New site: focus on long-tail keywords with KD under about 10–20 in Ahrefs terms.
- Established niche site: mid-range KD within your core topics.
- Strong authority site: competitive head terms, supported by clusters.
Difficulty vs opportunity
A difficult keyword can still be worth targeting if it is central to your business. Plan it as a long-term goal and support it with easier cluster content and link building. Combine difficulty with volume, business value and current rankings to prioritise.
Frequently asked questions
Is there a free keyword difficulty checker?
Several tools offer limited free checks, including Ahrefs’ free keyword generator and Moz’s free tier.
Why do I rank for “hard” keywords already?
Because your site’s relevance and authority in that niche outweigh the generic score.
Related terms
See backlinks, topical authority and the SEO encyclopedia.
Mr. SEO
Mr. SEO is the webmaster at SEO TT - SEO tips and tricks, a publication about all things SEO related.