How to read a keyword difficulty score without fooling yourself
Every tool computes difficulty differently, nobody publishes the formula, and a 42 in one tool is not a 42 in another. What the number is actually good for.
Keyword difficulty is the most-quoted and least-understood number in SEO. It appears in every tool, on a comfortable 0–100 scale, next to volume and CPC — which are measurements — and it borrows their credibility. It is not a measurement. It is an opinion, expressed as an integer.
That does not make it useless. It makes it useful for one job and misleading for three others.
What the number actually is
Every tool computes it roughly the same way: look at the pages currently ranking in the top ten, score how strong they are — links, referring domains, some authority proxy — and squash the result onto 0–100.
The differences are in the details, and the details are unpublished. How many results are sampled. Whether domain or page authority dominates. Whether on-page relevance counts at all. Whether the scale is linear or logarithmic — and it is almost always logarithmic, which is why 70 to 80 is a much bigger jump than 20 to 30.
So a 42 in one tool and a 42 in another are two different tools' opinions on two different scales. Comparing them is a category error, and yet the internet is full of "tool X shows a KD of 38 but tool Y says 55, which is right?" Neither. They are not measuring the same thing.
The one job it is good for
Ranking your own candidates against each other, within one tool, at one point in time.
That is it, and it is genuinely valuable. Given forty phrases you could write about, the difficulty column tells you which five to start with. That is a real decision and the number makes it better.
Three jobs it is bad for
Predicting whether you will rank. Difficulty describes the incumbents. It knows nothing about your site, your topical authority, your links, or whether the incumbent pages are actually any good. A 65 in a niche where the top ten are all thin affiliate pages is easier than a 35 where the top ten are all excellent.
Comparing across tools. See above.
Comparing across topics. Difficulty is calibrated on the whole index, so a 40 in a mature commercial space and a 40 in an obscure technical one are not comparable experiences.
What we do
We band it into three, and we say the bands are ours:
- 0–29, easy — a good page plus a few relevant links has a real chance
- 30–69, medium — you need genuine topical authority or a distinctly better page
- 70–100, hard — months, not weeks, and only if the phrase is worth it
Three bands rather than a hundred values, because a hundred values implies a precision that is not there. If you catch yourself preferring a keyword at 38 over one at 41, the scale has fooled you. They are the same keyword.
The check the number cannot do for you
Open the top five results and read them.
Ask: would I click mine over these? Is there a question all five leave unanswered? Are three of them from 2019? Is one of them a forum thread, which means Google could not find anything better?
That takes four minutes and beats the difficulty score every time. Use the number to decide which four minutes to spend — that is the job it is for.