Keyword difficulty is an opinion, not a fact
Keyword difficulty is a 0-100 score that estimates how hard it will be to rank on the first page of Google for a given term. Here is the part most guides skip: keyword difficulty is not a property of the keyword. It is each tool's guess, built from different inputs, which is why the same phrase can score 25 in Ahrefs and 48 in Semrush. Neither is wrong. They answer slightly different questions with slightly different data.
Understanding what goes into that number, and where it breaks, is the difference between using it as a rough filter and treating it as gospel while you burn three months on a term you were never going to rank for. This is a focused piece of our larger walkthrough on how to do effective keyword research; here we stay on the difficulty score itself.
What the score is trying to tell you
At its core, every keyword difficulty (KD) metric is a shortcut for one question: how strong are the pages already ranking, and how much authority would you need to muscle in? Backlinks remain one of Google's stronger ranking signals, so most vendors lean heavily on the link profiles of the current top 10 results.
The catch is that "how strong" has no universal definition. Tools weight backlinks, page authority, content quality and SERP crowding differently. The number that comes out is a compression of a messy reality into a single digit, and compression always loses information. It says nothing, for instance, about whether the ranking pages actually satisfy the searcher, which is what Google's own guidance on creating helpful, people-first content says its ranking systems reward.
How Ahrefs calculates keyword difficulty
Ahrefs' KD is deliberately narrow. Per Ahrefs' own methodology, the score is calculated almost entirely from one input: the number of referring domains pointing to the pages currently in the top 10. Ahrefs sampled a large set of keywords, plotted how many linking domains the top-ranking pages had, and mapped that curve onto a 0-100 scale. As a rough calibration, KD 0-5 means the top pages have barely any backlinks, KD 50 sits around a couple hundred, and KD 90+ means thousands.
That is it. Ahrefs KD does not factor in content quality, on-page optimisation, search intent, or domain-level authority. It is a link-count proxy. This makes it fast and consistent, but it systematically underrates keywords where the top pages have few links yet stay hard to beat because they come from trusted brands or precisely match search intent.
How Semrush calculates keyword difficulty
Semrush blends more signals. Per Semrush's methodology update, the company analysed over 100,000 keywords and 100-plus parameters, then weighted the ones that matter most: referring domains carry roughly 41% of the score, authority score about 17%, search volume around 9%, and the dofollow-to-nofollow ratio another 9%, with SERP features like featured snippets and ads folded in on top.
Because it stirs in more variables, Semrush usually produces higher numbers than Ahrefs for the same term. A keyword where the top pages have modest link counts but strong domains and a crowded SERP will score low on Ahrefs and moderate-to-high on Semrush. That is the mechanical reason behind the constant "why is Ahrefs KD lower than Semrush" question. It is not a bug. They count different things.
Ahrefs vs Semrush keyword difficulty at a glance
| Factor | Ahrefs KD | Semrush KD |
|---|---|---|
| Referring domains to top 10 | Primary, near-sole input | Largest single input (~41%) |
| Dofollow / nofollow ratio | Not weighted | Weighted (~9%) |
| Page / domain authority | Not included | Included (~17%) |
| Search volume | Not included | Included (~9%) |
| SERP features (snippets, ads) | Not included | Included |
| Personalised to your site | No (global only) | Yes (Personal KD) |
| Typical result | Lower number | Higher number |
Moz uses yet another model, blending its Page Authority and Domain Authority link metrics into the score, as described in Moz's explanation of keyword difficulty. Ubersuggest leans on a similar authority-plus-links approach. Four tools, four numbers, one keyword.
The real problem: difficulty is relative to your domain
Here is the insight most articles never state plainly. A single global KD number is the wrong abstraction, because difficulty is relative to the site trying to rank.
A keyword scored KD 50 is trivial for a site with a Domain Rating of 80 and thousands of referring domains. That same KD 50 keyword is effectively impossible for a three-month-old blog with no link authority. The keyword did not change. Your ability to compete did. A universal 0-100 score pretends everyone starts at the same line, and nobody does.
This is exactly why Semrush shipped Personal Keyword Difficulty, which recalculates the score against your specific domain's authority. It is an admission that the global number, on its own, is only half the picture. When you are starting out, the practical move is to hunt for terms where your authority is enough to compete, which is the whole point of finding low competition keywords and building toward harder terms over time.
Keyword difficulty vs search volume
People conflate these two constantly, so let me separate them cleanly. Search volume tells you how many people search a term per month. Keyword difficulty estimates how hard it is to rank. They are independent axes, and the sweet spot sits where volume is decent and difficulty is low.
- High volume, high difficulty: broad head terms like "project management." Great traffic if you win, but you probably will not for years.
- Low volume, low difficulty: specific long tail keywords like "project management software for civil engineering firms." Less traffic each, but far easier to win and often higher intent.
- High volume, low difficulty: the rare unicorn. Grab these immediately.
- Low volume, high difficulty: usually skip, unless the term has strong buyer intent that justifies the fight.
Never rank keywords by difficulty alone or by volume alone. The two numbers only mean something together, and both should be filtered through intent before you commit.
Is keyword difficulty accurate? The 30-second SERP scan
KD scores are directionally useful and frequently wrong on specifics. Because they compress so much into one number, they miss weak signals a human spots in seconds. Before committing to any keyword, open the actual SERP and scan the top 10 for these:
- Reddit, Quora, or forum threads on page one. If user-generated content is ranking, Google is struggling to find strong dedicated pages, and you can often outrank it with one focused article. Google has openly surfaced more forum and discussion content in results, so this is common.
- Stale results. Check publish and update dates. A top-5 page last touched in 2021 is beatable with fresh, current content.
- Thin or off-target pages. If the ranking pages do not answer the query well, intent is unmet and the door is open regardless of their link counts.
- Domain mismatch. If page 1 is all DR 80+ giants, the KD number matters less than the plain fact that you cannot compete yet.
This manual pass takes half a minute and routinely overrides the tool's score in both directions. It is the single most underused step in keyword research.
How to use keyword difficulty in practice
Here is a workflow that treats KD as a filter, not an oracle:
- Pull KD as a first-pass sieve, not a verdict. Cross-check the number against a second source when the stakes are high.
- Weigh it against your own domain authority. New sites should target lower KD bands; established sites can reach higher.
- Pair every candidate with search volume and confirmed intent before it makes the list.
- Run the 30-second SERP scan on your shortlist to catch signals the score missed.
- Group the survivors into topics and map them to pages, which flows into keyword clustering and keyword mapping.
You can also reverse-engineer difficulty by studying who already ranks. A structured competitor keyword analysis shows which terms sites at your level are winning, which is often a truer difficulty signal than any single score.
In DeployFlare's keyword research tool, KD sits alongside volume, intent and SERP data on one screen, so you are not tab-hopping between metrics that only mean something together. Pricing starts at ₹499/month, billed in INR with UPI and GST, and the same difficulty data covers city-level and vernacular SERPs (Hindi, Tamil, Marathi and more) that most Western tools ignore. If you are weighing options, our Ahrefs alternative comparison breaks down where the difficulty models actually differ.
The takeaway
Treat keyword difficulty as a fast, imperfect filter, never a final answer. Know which formula your tool uses, remember the number is relative to your own site, always pair it with volume and intent, and spend 30 seconds looking at the real SERP before you commit. The score narrows the field. Your judgment picks the winner.