What it is
Browser caching is an instruction your server attaches to files like images, CSS, and scripts, telling the browser how long it may keep a copy. With it, a returning visitor loads those files from their own device instead of pulling them down the network again. Without it, every visit fetches the same logo, stylesheet, and product photos from scratch, as if the shopper had never been there before.
How common it is
About half of audited stores (50%) set caching correctly. The audit checks the response on your store’s static files, the CSS and the images, for headers that let the browser store and reuse them. A store can serve light, well-made files and still fail, because the problem is not the files themselves but the missing instruction to keep them.
Why it costs you
The cost lands on the visit that matters most, the shopper who came back to buy. The first time someone arrives, everything downloads, which cannot be avoided. The second time, with caching off, their browser fetches the whole page again rather than reusing what it already has, so a returning customer waits as long as a stranger. These are people already close to a purchase, and the slow reload meets them at the worst moment. It is set once in the server configuration and then works automatically on repeat visits.
Check it in 30 seconds
Load your store, then reload it, with the Network tab open in your browser. Watch whether files come back marked “from cache” on the second load or download again. If everything re-downloads, caching is off. PageSpeed Insights flags the same thing as “serve static assets with an efficient cache policy.”
Read next: Ecommerce Site Speed: Convert More of Your Traffic
Run the free audit to see whether returning shoppers are reloading your whole store every visit.