Keyword difficulty (KD) is a score from 0 to 100 that estimates how hard it is to get a page into Google’s top 10 for a keyword. A higher score means a harder keyword, and every big SEO tool shows one. The catch is that each tool works it out in its own way.
That last part matters more than most people think. On October 9, 2026, we looked up the same 39 keywords in DataForSEO and in Ahrefs. The two scores were 14.8 points apart on average, and 10 of the 39 keywords were 20 points or more apart.
What keyword difficulty means
Keyword difficulty is a guess at how much strength a page needs to rank on page one, based on the pages that rank there now. Most tools measure that strength with backlinks, which are links from other websites.
Ahrefs puts it in plain numbers. Pages that rank for a keyword with a KD of 0 to 5 barely have any backlinks. Around KD 50 they tend to have a couple of hundred, and above 90 they have thousands.
The score never looks at your own site. It also does not judge whether the ranking pages are any good, or whether they answer the search at all, so it can only ever be a starting point.
How SEO tools calculate keyword difficulty
All the big tools start from the same idea: look at the top 10 results and measure the links behind them. After that, the math splits.
| Tool | What goes into the score | Scale |
|---|---|---|
| Ahrefs | How many websites link to each of the top 10 ranking pages | 0 to 100 |
| Semrush | Links to the ranking pages, the share of dofollow links, the Authority Score of the ranking sites, and traits of the keyword’s results page | 0 to 100% |
| DataForSEO | A link score for each top 10 page (90% weight) and its whole domain (10%), then the higher of the median or the average, rescaled | 0 to 100 |
The labels differ too. Semrush calls a score of 0 to 14 “very easy” and 85 to 100 “very hard”, and other tools draw those lines in other places.
Ahrefs is open about the problem. Its own guide says the tools share a 0 to 100 scale, but “each one calculates it differently”. So a 40 in one tool and a 40 in another are not the same thing.
We compared 39 keywords in DataForSEO and Ahrefs
To see how big the gap is in practice, we pulled keyword difficulty and monthly search volume for 39 keywords on October 9, 2026. We used DataForSEO Labs and Ahrefs Keywords Explorer, both set to the United States. The keywords are the SEO and SERP topics we research for this blog.
Here is what we found when we lined the two tools up:
- The average gap between the two scores was 14.8 points, and the median gap was 11 points.
- 10 of the 39 keywords differed by 20 points or more.
- Only 10 of the 39 landed within 5 points of each other.
- Neither tool was stricter overall. DataForSEO gave the higher score on 19 keywords, Ahrefs on 19, and they matched on 1. Their averages were close: 22.9 for DataForSEO and 21.4 for Ahrefs.
So on average the two tools agree, but on any single keyword they often do not. That is the case that matters, because you pick keywords one at a time.
| Keyword | DataForSEO KD | Ahrefs KD | Gap |
|---|---|---|---|
| google search parameters | 82 | 0 | 82 |
| people also ask | 45 | 4 | 41 |
| google ai mode | 37 | 75 | 38 |
| keyword clustering | 28 | 0 | 28 |
| does chatgpt use google | 28 | 0 | 28 |
| google custom search json api | 29 | 56 | 27 |
| what is a good bounce rate | 25 | 0 | 25 |
| web search api | 30 | 54 | 24 |
| website traffic checker | 42 | 66 | 24 |
| how to find all pages on a website | 0 | 20 | 20 |
| how to track ai overviews | 34 | 36 | 2 |
| ctr calculator | 2 | 0 | 2 |
| rank tracking api | 0 | 0 | 0 |
The first ten rows are every keyword with a gap of 20 or more. The last three show that the tools do agree sometimes.
Search volume split as well. DataForSEO put serp features at 390 searches a month and Ahrefs put it at 4,400, about 11 times more. For google ai mode it went the other way: 301,000 against 29,000.
Why the scores disagree
Three things push the numbers apart.
- Different link data. Each tool crawls the web on its own, so each one finds a different set of links.
- Different math. Ahrefs counts links to the ranking page. DataForSEO blends page and domain scores. Semrush adds authority and link types.
- Different snapshots. The top 10 changes over time, and each tool checks Google on its own schedule. A score can describe a results page that no longer looks like that.
None of this makes KD useless. It just means that one score is one tool’s opinion. Use it to sort a list inside that tool, and do not mix scores from two tools in one sheet.
How to judge keyword difficulty by reading the SERP
A score cannot see what you can see on the results page. Reading that page takes only a few minutes per keyword, and it often changes the answer you got from the score. Our step by step SERP analysis covers it in full. Here is the short version:
- Load the real page for your country and device, signed out, because your own browser is personalized.
- Note who ranks. Big brands, small blogs, forums, PDFs and help threads are very different rivals.
- Check the intent. If the top pages do not answer the search well, a page that does has an opening.
- Count what sits above the links. AI Overviews, ads and videos push the first result down. Our guide to SERP features shows what each block does to clicks.
- Compare with your own site. A new site should look for top 10s that include weak or off-topic pages.
Example 1: google search parameters (DataForSEO 82, Ahrefs 0)
We fetched the US desktop results for this keyword on October 9, 2026. The top eight included a Semrush PDF, a forum thread, a Google community thread and five blog posts. Seven of the eight were about search operators like site:, not the URL parameters the keyword asks about.
Neither score tells that story. The real signal is a mix of weak page types and a poor match for what the searcher wants. A page that answers the actual question has a fair shot, which is why we wrote our list of Google search parameters.
Example 2: keyword clustering (DataForSEO 28, Ahrefs 0)
Ahrefs says 0, which sounds easy. But the US top 10 on the same day included Semrush, Surfer, SE Ranking, Keyword Insights and Wikipedia. A KD of 0 suggests those pages have few links of their own, and links to the page are what Ahrefs counts. Yet four of those five sites are well-known SEO tool companies, and the fifth is Wikipedia.
A small site will find it hard to beat them with one more general guide. A different angle has a better chance, such as working code that clusters keywords from real results. That is the approach in our guide on how to cluster keywords.
How to check keyword difficulty for a whole list
- Pull KD and volume for every keyword from one tool.
- Sort by KD and drop the keywords that are clearly out of reach for your site.
- Read the results page for the rest, using the five checks above.
- Write down your call for each keyword: go, wait or skip.
Step 3 is the slow part when the list is long. For hundreds of keywords, you can pull the results pages as data with a SERP API. Then count forums, PDFs and big brands in a sheet instead of by hand.
Frequently asked questions
How do you measure keyword difficulty?
Start with the KD score from one SEO tool to sort your keyword list. Then open the real Google results for the keywords you like and look at who ranks, how strong those pages are, and whether they match what the searcher wants. The score is a first filter, and the results page is the real test.
What is a good keyword difficulty score?
There is no single good number, because it depends on how strong your own site is. Ahrefs says pages that rank for keywords with a KD of 0 to 5 barely have any backlinks, so low scores are a fair place for a new site to look. Always check the results page before you commit.
Why do Ahrefs and Semrush show different keyword difficulty?
Each tool uses its own link database and its own formula, and each checks Google on its own schedule. Ahrefs counts the sites that link to the top 10 pages. Semrush also mixes in authority scores and link types. The same keyword can get very different scores as a result.
Does a keyword difficulty of 0 mean it is easy to rank?
Not always. A 0 in Ahrefs means the pages in the top 10 have few sites linking to them. It does not look at how strong those websites are overall. On October 9, 2026, Ahrefs scored keyword clustering at 0, yet Semrush, Surfer and SE Ranking all ranked in the US top 10.