Every keyword tool gives you a difficulty score, and almost nobody explains what it’s actually measuring. You just learn to treat low numbers as green lights and high numbers as red ones, without knowing why — which works fine until two tools disagree with each other by 30 points on the same keyword, and you’ve got no idea which one to believe.
Here’s what’s actually going on under the number.
What the score is actually measuring
Mostly: how many backlinks the pages currently ranking on page one already have. That’s it. Not how hard the topic is to write about, not how much competition exists in your market, not how good the content needs to be — just an estimate of the link-building effort required to outrank what’s already there.
Ahrefs’ version, for example, is built almost entirely on referring domains to the current top 10 — their own numbers suggest you need roughly 56 referring domains to break into the top 10 for a KD 40 keyword, and around 249 for KD 60. Mangools’ KWFinder works similarly, scoring 0 to 100 based on the link profile strength of the ranking pages. Semrush goes further, blending referring domains with the ratio of dofollow to nofollow links, the authority of the ranking domains, search volume, and which SERP features are present.
None of them are measuring whether you can write something good enough to rank. They’re measuring whether you can out-link what’s already there.
Why two tools can show wildly different numbers for the same keyword
Because they’re not measuring the same thing, even though they’re both calling it “difficulty.” A keyword might show KD 23 in one tool and 58 in another — not because one is wrong, but because each has built its own formula, weighted differently, calibrated against a different index of the web.
The practical implication: never compare a KD score between tools. Pick one, learn how it behaves on keywords you already understand, and use it consistently. Comparing an Ahrefs KD to a KWFinder KD is like comparing degrees Celsius to degrees Fahrenheit and wondering why the numbers don’t match.
The bit most tools don’t tell you: it doesn’t know your site
A generic difficulty score treats every reader the same, whether you’re a brand-new blog or a site with five years of backlinks behind it. Semrush has started addressing this with a “Personal” difficulty score that adjusts for your own domain’s authority — a KD 50 keyword might show as far more achievable for an established site than for a new one. Most tools, KWFinder included, don’t do this: the number you see is the same whether you published your first post yesterday or five years ago.
That means the score is a starting point, not a verdict. A “beatable” KD 25 keyword is a lot less beatable if you’re three weeks old with no backlinks. A “tough” KD 45 keyword might be entirely realistic if you’ve already got some domain authority behind you.
When to override the number with your own judgement
When the SERP is stuffed with features that eat the click before anyone reaches your result. A low-difficulty keyword where Google answers the question directly in a featured snippet, or where the top results are all videos, isn’t the easy win the score suggests.
When you’re new. Treat every score as more optimistic than reality for the first several months of a new site, regardless of what tool you’re using.
When the ranking pages are big brands, regardless of the number. A surprisingly low difficulty score sitting under a page one stacked with major publications usually means the tool’s link-based formula hasn’t caught up with a ranking factor it isn’t measuring — brand signals, content depth, or user engagement data Google has but the tool doesn’t.
The practical rule
Use the difficulty score to build a shortlist, fast. Then open the actual search results for anything on that shortlist and look at who’s really there — how strong they look, what format they’re using, whether there’s a snippet in the way. The score gets you to the right ten keywords out of a hundred. Your own eyes should make the final call on which of those ten to write.
A keyword difficulty score isn’t a verdict. It’s a shortcut to the ten keywords worth actually looking at properly.
If you want a tool that makes that shortlist fast without a five-figure annual bill, Mangools’ KWFinder is the one I use — full details in my Mangools review.
Frequently asked questions
What does a keyword difficulty score actually measure?
Mostly the strength of the backlink profiles behind the pages currently ranking on page one — not how hard the topic is to write about, and not how much market competition exists.
Why do Ahrefs, Semrush, and KWFinder show different difficulty scores for the same keyword?
Each tool uses its own formula and its own index of the web. The numbers aren’t measuring identically, so they shouldn’t be compared to each other — pick one tool and stay consistent.
Should I trust a low difficulty score on a brand-new site?
Treat it as more optimistic than reality. Most difficulty scores don’t adjust for your own site’s authority, so a keyword that looks easy for an established domain may take considerably longer for a new one.
Affiliate disclosure: some links in this post are affiliate links. If you sign up through them it costs you nothing extra and helps keep this site running. I use Mangools myself.