For keyword research, Semrush and Ahrefs are closer than their marketing suggests. Both index almost exactly the same number of keywords (28.8 billion for Semrush, 28.7 billion for Ahrefs, per their own pages in October 2026). Ahrefs is the better pick if you judge keywords by the traffic the top page actually gets (Traffic Potential, Parent Topic) and want a cheap way in ($29 Starter or $129 Lite). Semrush is the better pick if you also run Google Ads or want one suite for SEO, PPC and content, starting at $139 a month. Neither keyword difficulty score is "accurate": they measure different things, so learn one and stick with it.
Below: the head-to-head table, how each KD score is calculated and why they disagree, what accuracy studies show, prices as of October 2026, and a short quiz to pick yours.
Key takeaways
- Database size is a tie. Semrush lists 28.8B keywords in 142 country databases; Ahrefs lists 28.7B keywords across 217 locations.
- Ahrefs KD looks only at links. It is a weighted average of the linking domains pointing to the top 10 pages, on a logarithmic 0 to 100 scale.
- Semrush KD% blends median referring domains, the dofollow-to-nofollow ratio, the Authority Score of ranking domains and SERP traits. The same keyword can score very differently in each tool.
- For traffic estimates, both published studies found Ahrefs closer to Search Console (48.63% vs 61.58% average error in a 184-site study).
- Cheapest real keyword research as of October 2026 is Ahrefs Starter at $29 a month (200 credits). Semrush's paid plans start at $139.
Semrush vs Ahrefs for keyword research: the short comparison
| Semrush | Ahrefs | |
|---|---|---|
| Keyword database | 28.8B keywords, 142 country databases | 28.7B keywords (filtered from 110B discovered), 217 locations |
| Main tool | Keyword Magic Tool, Keyword Overview, Keyword Strategy Builder | Keywords Explorer |
| Difficulty score | KD% (links, authority, link mix, SERP traits) | KD (linking domains to the top 10 only) |
| Standout metric | Intent labels, CPC and competitive density from its ads data | Traffic Potential and Parent Topic (what the #1 page really earns) |
| Competitor keyword gaps | Keyword Gap | Competitive Analysis (Content Gap) |
| AI helpers | AI features across the suite, SEO + AI Search plans | AI suggestions, keyword clusters, intents (Standard plan and up) |
| PPC keyword data | Strong (ads history, CPC, competition) | Basic (CPC) |
| Free option | Free account: 10 reports a day | Ahrefs Free (site data only, no Keywords Explorer) and free keyword tools |
| Entry price for keyword research | $139/mo (SEO plan) | $29/mo (Starter, 200 credits) or $129/mo (Lite) |
Keyword difficulty: Semrush vs Ahrefs
This is the biggest practical difference, and the one most comparisons gloss over. Both tools output a number from 0 to 100, which tempts people to compare them. Don't: they are built from different inputs.
Ahrefs KD estimates how hard it is to reach the top 10 in a given country. According to Ahrefs' metric documentation, it is calculated from the number of linking domains pointing to the top-ranking pages, using a weighted average with outliers removed, plotted on a logarithmic 0 to 100 scale. Ahrefs' own example: a KD 6 keyword needs about 7 referring domains to reach page one. It considers backlinks only, so Ahrefs itself recommends reviewing the top 10 manually.
Semrush KD% is, per its knowledge base, based on the median number of referring domains to the ranking URLs, the median ratio of dofollow to nofollow links, the median Authority Score of the ranking domains, and the SERP qualities of the keyword itself. Its bands: 0-14 very easy, 15-29 easy, 30-49 possible, 50-69 difficult, 70-84 hard, 85-100 very hard.
| Ahrefs KD | Semrush KD% | |
|---|---|---|
| Inputs | Linking domains to the top 10 pages | Referring domains, dofollow ratio, domain Authority Score, SERP traits |
| Scale | 0 to 100, logarithmic | 0 to 100, six named bands |
| Considers your site's strength | No | No |
| Considers content quality or intent | No | Partly (SERP traits) |
| Best read as | "Roughly how many links will I need?" | "How strong are the sites I'm up against?" |
Why the same keyword scores differently: a SERP full of strong domains whose specific pages have few links (forums, big brands' thin pages) scores low in Ahrefs and higher in Semrush, because Semrush weighs domain authority. A SERP of small sites with heavily linked pages does the opposite.
Which keyword difficulty is more accurate?
Neither, in the sense of predicting whether you will rank. Both ignore your own site's authority, topical coverage and content. The useful question is which score you can calibrate, and you can calibrate either in 20 minutes:
- In Google Search Console, export the queries where your site ranks in the top 10 (Performance → Queries, filter position below 10.5).
- Look up their KD in your tool of choice.
- The 80th-percentile KD of keywords you already rank for is your realistic ceiling today. Target at or below it, and raise it as your backlinks grow.
For most young sites that ceiling is low. Across the 200,871 articles Outrank wrote for 4,348 customer sites in the 90 days to October 2026, the median target keyword had a difficulty of 14 out of 100, and 63% were under 20 (Outrank platform data). Our guide to keyword difficulty and to finding low-competition keywords goes deeper.
Search volume and traffic accuracy
Both tools show search volume as a 12-month average, and both vendors have published studies concluding their own numbers are closest to Search Console impressions (Semrush in a 10,000-keyword study in 2022; Ahrefs in its own tests). Vendor studies cancel each other out. Ahrefs' own 2024 piece concedes that no tool's volume is accurate, only "directionally accurate".
Traffic estimates have independent data, and Ahrefs comes out ahead:
| Study | Ahrefs | Semrush |
|---|---|---|
| Collaborator / Promodo, 184 sites, H1 2024 | 48.63% average error, tends to underestimate | 61.58% average error, overestimated 112 of 184 sites |
| Ahrefs, 1,635 sites, 2022 (vendor-run) | 49.52% median deviation, 0.76 correlation | 68.36% median deviation, 0.74 correlation |
This matters for keyword research when you size an opportunity by looking at what competing pages earn. Our analysis of how accurate Semrush is includes a calculator to test both tools against your own Search Console data.
Keyword research features compared
Finding ideas. Semrush's Keyword Magic Tool groups ideas by topic and lets you filter by intent, volume, KD%, SERP features and word count. Ahrefs' Keywords Explorer splits ideas into matching terms, related terms and search suggestions, with filters for the same basics. Both find long-tail questions well.
Judging a keyword. Ahrefs' Traffic Potential (the total organic traffic of the #1 page across all its keywords) and Parent Topic (the broader query that page ranks for) are the most useful single metrics either tool has: they stop you from writing five articles for five phrasings of one topic. Semrush counters with intent labels on every keyword and richer CPC and competitive density data from its ads database, which helps you spot commercial terms.
Clustering and planning. Ahrefs offers AI suggestions, keyword clusters and search intents in Keywords Explorer on its Standard plan and above. Semrush's Keyword Strategy Builder turns a seed list into pillar and cluster pages. See what keyword clustering is if you plan content this way.
Competitor gaps. Semrush's Keyword Gap compares up to five domains in one view; Ahrefs' Competitive Analysis shows keywords competitors rank for and you don't. Both work; Semrush's view is a little quicker to read. More in our keyword gap analysis guide.
Pricing for keyword research (October 2026)
| Plan | Price (monthly billing) | What you get for keyword research |
|---|---|---|
| Semrush Free | $0 | 10 reports a day across tools |
| Semrush SEO | $139/mo ($117.33/mo billed annually) | "Basic keyword research and competitor analysis", 500 tracked keywords |
| Semrush Starter (SEO + AI Search) | $199/mo | Full keyword research and optimization tools, plus AI visibility tracking |
| Semrush Pro+ | $299/mo | Adds historical data, cannibalization analysis, content optimization |
| Ahrefs Free | $0 | Data on your own verified sites; no Keywords Explorer |
| Ahrefs Starter | $29/mo | Keywords Explorer and Site Explorer with 200 credits a month, monthly only |
| Ahrefs Lite | $129/mo | 1,000 credits per user, 750 tracked keywords |
| Ahrefs Standard | $249/mo | Unlimited credits; AI suggestions, keyword clusters, intents |
| Ahrefs Advanced | $449/mo | More history, users and limits |
Prices from Semrush and Ahrefs pricing pages, checked October 19, 2026. Both offer up to 17% off for annual billing.
Semrush or Ahrefs: which should you choose?
4-question decision helper
Semrush or Ahrefs for your keyword research?
Question 1 of 4
Besides keyword research, what will you use the tool for most?
Cheaper alternatives for keyword research
If neither price fits, these cover most keyword research needs:
- Google Keyword Planner: free with a Google Ads account; volume ranges unless you run ads. Good for validating volume.
- Google Search Console: free and the only source of your real queries and impressions. Underused for keyword research.
- KWFinder (Mangools) and KeySearch: cheaper keyword-focused tools with their own difficulty scores; see Ahrefs vs KWFinder.
- Ubersuggest and similar budget suites: fine for ideas, lighter on data depth.
- Outrank: if you mainly research keywords to write blog posts, Outrank includes unlimited keyword research with live volume and difficulty, chooses targets your site can win, and writes and publishes the articles. It is not a replacement for Semrush or Ahrefs if you need competitor or backlink analysis.
FAQ
Is Ahrefs better than Semrush for keyword research?
For pure keyword research, Ahrefs has the edge on judging opportunity (Traffic Potential, Parent Topic), the cheaper entry plan and, in two studies, closer traffic estimates. Semrush has the edge if you need PPC data, intent labels on every keyword and a broader all-in-one suite. Their keyword databases are the same size.
Which keyword difficulty is more accurate, Semrush or Ahrefs?
Neither predicts whether your specific site will rank, because neither considers your site's authority or content. Ahrefs KD reflects the links pointing to the top 10 pages; Semrush KD% adds domain authority, link mix and SERP features. Calibrate whichever you use against keywords you already rank for in Search Console.
Why do Semrush and Ahrefs show different keyword difficulty for the same keyword?
They use different formulas. Ahrefs counts linking domains to the top-ranking pages on a logarithmic scale, while Semrush blends referring domains, the dofollow-to-nofollow ratio, the Authority Score of ranking domains and SERP traits. A results page with strong domains but weakly linked pages will look harder in Semrush than in Ahrefs.
Is Semrush or Ahrefs cheaper?
Ahrefs has the cheaper entry point: Starter at $29 a month with Keywords Explorer and 200 credits, then Lite at $129. Semrush's paid plans start at $139 a month for the SEO plan, $199 for Starter and $299 for Pro+, as of October 2026. Semrush's free account gives 10 reports a day.
Can you do keyword research with free versions of Semrush or Ahrefs?
Partly. Semrush's free account allows 10 reports a day, enough for a handful of keyword lookups. Ahrefs Free doesn't include Keywords Explorer, but Ahrefs offers free keyword generator and difficulty checker tools. Pair either with Google Keyword Planner and Search Console for a capable free setup.
