Readability score for SEO: does it matter?
·4 min read
A readability score does not affect your rankings directly. Google has never said it computes Flesch-Kincaid, Gunning Fog or any other formula for ranking, and its own guidance talks about clear, well-written content without naming a score. It is still a useful diagnostic. It points at the long sentences and heavy words that lose readers and that AI answers struggle to quote. Use it to find what to rewrite, never as a number to hit.
Does Google use a readability score?
No published Google document says it does. Google writes about outcomes for the reader instead.
Its guide to creating helpful, people-first content asks "Does the content have any spelling or stylistic issues?" and lists clear writing as one sign of the skill behind a satisfying page. It never mentions a readability formula, and it answers the word count question bluntly. Google has no preferred length.
The AI features guide says the same thing for AI Overviews and AI Mode. It tells you to make content "well written and easy to follow", organized into paragraphs and sections under clear headings. It adds that there is no need to break content into tiny pieces for AI.
So when an SEO plugin turns red below 60, that threshold is the plugin's rule. Treat the score like a spellchecker, not a ranking signal.
Which readability formula should you use?
Any of the three common ones, as long as you stick with it. Each counts sentence length and word length and maps the result to a US school grade. They differ in how they define a hard word.
| Formula | What it counts | Output | Origin |
|---|---|---|---|
| Flesch-Kincaid grade level | Words per sentence, syllables per word | US grade | Kincaid and colleagues for the US Navy, 1975 |
| Gunning Fog index | Words per sentence, share of words with 3+ syllables | Years of schooling | Robert Gunning, 1952 |
| SMOG | Words with 3+ syllables across 30 sentences | Grade needed to fully understand | G. Harry McLaughlin, Journal of Reading, 1969 |
Flesch-Kincaid weighs every syllable. Gunning Fog and SMOG count only words of three or more syllables as hard and punish them heavily, which makes them stricter on jargon-heavy B2B copy. SMOG was normed on 30-sentence samples, so it is unstable on a short product page.
Expect them to disagree by a grade or two. Track one over time and compare a page only with itself. The formula, the 0 to 100 scale and a worked rewrite for Flesch reading ease are in our Flesch reading ease guide.
Why readable passages get quoted in AI answers
AI search engines retrieve passages, not whole pages. A passage gets quoted when it states one claim in words a model can lift without the paragraph around it. The habits that lower a readability score are often the same ones that make a passage hard to quote.
Take this sentence from a hypothetical software page.
As a result of this, it is generally recommended that organizations considering the implementation of such a solution evaluate their existing infrastructure, since the complexity of integration can vary considerably depending on a number of factors.
It is one 36-word sentence with 13 words of three or more syllables. Our analyzer scores it at grade 23.7 with a Gunning Fog of 28.8. Worse for an AI answer, it never says what "this" or "such a solution" is. Quoted alone, it means nothing.
Check your current login system before you add single sign-on. Setup takes longer when you have many apps that each store their own passwords.
Two sentences, 24 words, grade 5.8. Each sentence names its subject, so either one survives being cut out and pasted into an answer.
The formula did not catch the missing subject. It caught the long sentence the missing subject was hiding in, and that is the usual pattern. The score flags the passage and a human finds the real problem. For the quoting side in depth, read how to write passages AI can quote and our sibling post on citable content.
How to improve your readability score
Fix the sentences the score is reacting to, in this order.
- Split sentences over 40 words. They are almost always two points joined with "and", "which" or "since". Make each one its own sentence.
- Replace abstract nouns with verbs. "The implementation of" becomes "adding". "Perform an evaluation of" becomes "check".
- Name the subject. Replace "this", "it" and "such" at the start of a paragraph with the thing you mean.
- Keep the precise long word. If "authentication" is the right term, use it and define it once. Swapping it for something vaguer raises the score and costs the reader.
- Put the answer first under each heading. No formula rewards this, and it matters more than any grade.
Grade 8 suits pricing, help and service pages. Developer docs can sit at grade 12 and be perfectly clear.
Check the readability score of any page
Our readability analyzer scores a public URL or up to 20,000 characters of pasted text. On a URL it reads the main content and skips navigation, headers, footers, headings, code and tables, so the score covers the prose. It does not run JavaScript, so paste copy that loads client-side.
It returns Flesch reading ease, Flesch-Kincaid grade and Gunning Fog, with the counts behind them. It flags sentences of 25 words or more as long and 40 or more as very long, and lists up to 10 rewrite targets with the reason for each. It does not compute SMOG, does not rewrite anything and withholds the scores for non-English copy. Each run costs 5 credits.