A keyword gap is the set of search terms that one or more competing websites rank for and your site does not, or ranks well below them for. Keyword gap analysis is the process of comparing the sites to find those terms and decide which are worth going after.
How keyword gap analysis works
SEO platforms such as Semrush and Ahrefs keep large databases of the keywords each website appears for in Google, split by country. A gap report puts your domain alongside several competitors and lines up the results. Semrush, for instance, sorts them into groups such as terms every competitor ranks for and you do not, terms where you rank below all of them, and terms where at least one competitor ranks and you do not. Ahrefs offers an equivalent comparison.
The output is only as good as the database behind it. Tools track a sample of all searches, and their rankings and volumes are estimates. Set the database to the United Kingdom, or you will be comparing against rankings in markets you do not serve.
Choosing who to compare against matters more than the tool. Your search competitors are not always your business competitors. A family law firm in Manchester competes in search with other firms, but also with Citizens Advice, GOV.UK, legal directories and national firms with large guide libraries. For gap analysis, pick sites that rank for the topics you want, of a broadly similar size, and that serve similar customers. That choice is a narrower form of competitor analysis.
Why it matters
A gap report turns guesswork about “what should we write next” into a list grounded in what people already search for and what Google already rewards. Picture a kitchen fitter in Leeds comparing itself with three local rivals. The report might show those rivals appearing for searches about kitchen fitting costs, how long a fit takes and particular styles of kitchen, none of which its own site addresses. Some of those are services it offers but never explains; others are buying questions it could answer better than anyone.
It also shows weak spots: terms where you have a page but rank on page two while competitors sit at the top. Improving those pages is often quicker than writing new ones.
Common mistakes
- Comparing against giants. Putting your site next to Amazon, the BBC or Wikipedia produces thousands of irrelevant terms.
- Copying the list wholesale. A competitor may rank for services you do not offer, areas you do not cover or topics with no buying intent.
- Skipping the cannibalisation check. New pages written straight from the report can end up competing with pages you already have.
- Confusing it with a content gap. A content gap analysis looks more broadly at topics, questions and angles your content does not cover, including ones no tool tracks.
- Trusting the volumes as exact. They are modelled estimates, useful for ranking options against each other.
How to act on it
Pick three to five genuine search competitors, run the comparison in the UK database, and export the missing and weak groups. Filter out anything irrelevant to what you sell or where you work. Group what remains by meaning, which the keyword clustering tool speeds up, so related searches are handled by one page rather than many.
Then decide where each group belongs. Some will strengthen an existing page, some justify a new one, and some are best left alone. Recording that decision in a keyword map keeps the plan tidy, and checking each group’s keyword difficulty alongside its value helps you order the work. This comparison is a standard part of my keyword research process.