Keyword Difficulty Explained: Why Every Tool Disagrees

Keyword difficulty (KD) is a score, usually from 0 to 100, that estimates how hard it would be to rank on the first page of Google for a given keyword. A low number suggests a winnable term, a high number suggests a fight against strong, established pages. The catch is that every tool calculates it differently, so the same keyword can score 25 in one tool and 40 in another. That is not a bug: KD is an estimate built from each tool’s own formula and data, not a figure Google publishes. This guide explains what KD really measures, why the tools disagree, and how to use it to pick keywords you can actually win, whatever number your tool shows.

What keyword difficulty actually measures

Keyword difficulty is an attempt to answer one question: how strong is the competition currently ranking for this term? Each tool looks at the pages on page one of Google and scores how hard they would be to displace, then expresses that as a single number. Most formulas lean heavily on the backlink strength of the ranking pages, because links remain a major ranking signal, but they also fold in other factors to varying degrees. The important mental model is that KD describes the competition, not the keyword itself. A keyword is not inherently “difficult”, it is difficult because specific strong pages currently rank for it. Change the SERP and the difficulty changes. That is why KD is a guide to prioritisation, not a law of physics.

Why every tool gives a different score

Tools disagree because they use different inputs and different formulas, and none of them can see Google’s actual ranking system. The table below shows roughly what each popular tool’s difficulty score leans on. The scores diverge because one tool may weight raw backlink counts heavily while another weights the authority of the ranking domains, or the on page relevance, or the search intent mix. They also draw on different backlink and keyword databases of different sizes, so even the underlying data differs before any formula runs. It is common to see the same UK keyword scored several points apart across tools, which is entirely normal. The lesson is not to hunt for the “correct” number, but to pick one tool and read its scores consistently.

Tool	Difficulty metric	Mainly based on
Semrush	Keyword Difficulty (KD %)	Authority of ranking pages, backlinks and other signals
Ahrefs	Keyword Difficulty (KD)	Backlink profiles of the top ranking pages
Moz	Keyword Difficulty	Page and domain authority of the results
SE Ranking	Keyword Difficulty	Strength of the pages currently ranking

How accurate is keyword difficulty?

Keyword difficulty is directionally accurate rather than precise, and you should treat it that way. It reliably tells you the difference between an easy term and a very hard one: a KD of 10 really is more winnable than a KD of 70, in any tool. What it cannot do is promise that a KD 25 keyword takes exactly twice the effort of a KD 12 one, or that the same score means the same thing in two different tools. Accuracy also drops for local and very long tail searches, where the tools have thin data and the real competition is often weaker than the score suggests. The honest way to use KD is as a filter and a sorter, not a guarantee. Combine it with a manual look at the actual SERP, which is the only way to see whether the results are genuinely strong or just old and thin.

The one check KD cannot replace: reading the SERP

The single most useful thing you can do is open the search results for your keyword and look at who ranks. KD is a summary of that SERP, but the summary hides detail that decides whether you can win. Are the top results genuinely authoritative, or are they forum threads, thin listicles and out of date pages you could clearly beat with a better answer? Do the ranking pages actually match the searcher’s intent, or has Google settled for near misses because nothing better exists? A KD of 35 in front of ten weak, off intent pages is more winnable than a KD of 20 in front of ten strong, perfectly matched ones. This is why our keyword research process always pairs the difficulty score with a manual SERP check before committing to a target.

How to use KD to pick winnable keywords

Here is the practical workflow, whichever tool you use. It turns a difficulty score from a number you stare at into a decision you can act on.

1. Filter your keyword list to a realistic ceiling for your site: KD 0 to 19 for a brand new domain, up to 29 as you build authority.
2. Sort the filtered list by search intent, keeping the terms that match a page you can genuinely make the best answer to.
3. Open the SERP for your top few candidates and judge the real competition by eye.
4. Favour keywords where the ranking pages are beatable: thin, old, off intent, or from sites no stronger than yours.
5. Group related low difficulty terms into one topic and target the cluster with a single strong page.

Follow that and you stop chasing high difficulty vanity terms and start winning the ones that actually move traffic. Our guide to finding long tail keywords shows how to build a list full of these lower difficulty opportunities. For how the tools that show KD compare, read Semrush vs Ahrefs, and browse our SEO tools hub for the wider field.

Frequently asked questions

What is a good keyword difficulty score to target?

For a new or low authority site, target keywords with a difficulty of 0 to 19, then raise the ceiling toward 29 as your site earns authority and rankings. High difficulty terms are worth planning for later, but chasing them early usually wastes effort you could spend winning easier terms.

Why do Semrush and Ahrefs show different keyword difficulty?

Because they use different formulas and different databases. Semrush blends the authority of ranking pages with backlinks and other signals, while Ahrefs focuses more on the backlink profiles of the top results. Neither is Google’s own figure, so the numbers naturally diverge. Pick one tool and read it consistently.

Is keyword difficulty accurate?

It is directionally accurate. It reliably separates easy terms from hard ones, but the precise numbers are estimates and mean different things across tools. Accuracy is weakest for local and long tail searches. Always pair the score with a manual look at the real search results.

Does Google use keyword difficulty?

No. Keyword difficulty is a metric invented by SEO tools to estimate ranking competition. Google does not publish or use a keyword difficulty score. It is a planning aid built from each tool’s own view of the search results, not a signal inside Google’s ranking system.

How do I find low difficulty keywords?

Use a keyword tool’s difficulty filter to cap results at a low ceiling, focus on longer, more specific phrases, and check the actual SERP for weak competition. Our guide to the Semrush Keyword Magic Tool shows the exact filters for surfacing low difficulty terms quickly.

Can I trust keyword difficulty for local searches?

Only loosely. Tools hold thin data for local and postcode level searches, so difficulty scores there are less reliable and often overstate the challenge. For local terms, trust a manual SERP check and your knowledge of the local competition more than the number the tool shows.