Accessibility vendors sell SEO as a free extra, and about half of that is real. Start with the part that is not. Google has no WCAG compliance ranking factor. Passing an accessibility audit does not improve your search position by itself, and accessibility appears nowhere in Google's own published list of the systems that rank pages.
What is true is narrower and more useful. A few things you do for accessibility are things Google has documented itself using, so you get the benefit twice for one piece of work. The trick is knowing which ones, because the industry list is longer than the evidence.
The Four Overlaps Google Documents
- Alt text. Google says it uses alt text, alongside computer vision and the page's own content, to work out what an image is about, and calls it the most important metadata an image carries. You write it for blind readers and it does a second job on the way past.
- Headings as content signals. Google reads your headings to work out what the page is about. Real heading elements, rather than large bold paragraphs, are what it has to read.
- Link text. Google says anchor text tells both users and Google something about the page on the other end. Click here tells a crawler exactly as much as it tells a screen reader user, which is nothing.
- Page titles. The title element is one of the sources Google uses to build the headline of your search result. It is also rule 2.4.2, which asks that a page have a title describing its topic or purpose. Same tag, two audiences.
The Claims Nobody Can Source
Two more overlaps get repeated everywhere in our industry, this site included until today, and neither has a Google document behind it. We went looking properly rather than repeating them again.
Transcripts and captions are the big one. Google's video guidance does not mention transcripts, captions, subtitles or audio content anywhere in what it says about indexing, and the nearest thing to an answer we could find is a 2010 note saying there was no way to indicate a transcript and perhaps there would be one later. So the honest version is this. A transcript is your audio written down, which puts words on the page that a crawler can read, and words on a page are the only thing it ever reads. That is worth having. It is not the documented search benefit it gets sold as, and a podcast without a transcript is not invisible.
Semantic HTML is the other. Giving a crawler a structure it can follow without guessing sounds obviously right, and we could not find Google saying anything about semantic markup as such anywhere. Do it because assistive technology gets role and state out of it for free. Do not put it on the invoice.
The Two Google Denies Outright
Heading order is the first. Google's position is that semantic order is fantastic for screen readers, and that from Search's point of view it does not matter if you use them out of order. That sentence is worth keeping somewhere, because it is the company everybody is optimizing for saying that heading structure is an accessibility concern rather than a search one.
The page language attribute is the second. Google does not use hreflang or the HTML lang attribute to work out what language a page is in, and says so directly. It uses the visible content instead. The attribute is still a Level A requirement, because a screen reader needs it to choose the right voice, and it buys you nothing at the search engine.
Where the Pitch Overreaches
Contrast ratios, focus indicators, target sizes, motion controls and error wording matter enormously to people and not at all to crawlers. Any product marketed as improving both is describing four items and charging for twelve. An overlay widget claiming both is a separate problem, and the documented record covers it without needing an SEO argument at all.
The way we would put it
Build for accessibility because people need it, then take the search benefit as work you did not have to pay for twice. And notice what happened in the middle of this page. Two claims we had been repeating for years did not survive being checked against the source, on a page whose whole argument is that nobody checks them. That is the test we would want you to run on anybody selling you either one, including us.