Primary and secondary
You pick two categories and most developers pick the biggest one that fits. That is usually the wrong call, because your category decides which chart you are ranked in, and being visible in a small chart beats being invisible in a large one.
The same app, the same downloads, two honest category choices. Only one of them puts it on a chart anybody sees.
The short version
Fewer competitors, same downloads, better rank.
Review rejects it and wrong-fit users leave.
A free second surface most apps leave blank.
If the leaders have millions of ratings, pick elsewhere.
Your primary category determines which top-charts you are ranked in and which category browsing surfaces can show you. It is a placement decision, not a filing decision.
The practical consequence: the same number of downloads puts you at #12 in a smaller category and #340 in a larger one. One of those is a position people see.
Rank 12 in a small category beats rank 340 in a big one, on identical downloads.
Among the categories that genuinely describe your app, the smaller one is usually the better choice, because you are competing against fewer apps for the same chart positions.
The limit is honesty. Apple's review team rejects category choices that do not match what the app does, and a user arriving from the wrong category leaves immediately, which costs you more than the chart position gained.
Most apps get a secondary category. It gives you a second surface to be discovered on at no cost to the first, and it is frequently left blank.
Use it for the next most honest fit rather than the next biggest. The same logic applies: a smaller second category is one where you can actually place.
If your secondary category is blank, you are giving away a free placement.
Before committing, look at the apps currently charting in each candidate category. If the top of the chart is dominated by apps with millions of ratings, the chart is not a realistic target however well the category describes you.
Compare that against the smaller alternative. A category where the leaders have tens of thousands of ratings rather than millions is a place a new app can reach a visible position in a reasonable time.
What people ask
It decides which chart you are ranked in, which changes how visible the same performance is.
Category does not change how Apple matches your keywords to a search. It determines which top-charts and browsing surfaces you appear on. The same download numbers can place you highly in a smaller category and nowhere in a larger one, which is why the choice matters.
Usually not. A bigger category has more competition for the same chart positions, so your app needs far more downloads to reach a place anybody sees. Among categories that honestly describe your app, the smaller one is generally the better placement.
Yes, through App Store Connect, and the change goes through review with your next version. It is worth getting right early, because chart position builds over time and moving category restarts that.
It gives you an additional discovery surface at no cost to your primary placement, and many apps leave it blank. Set it to the next most honest fit for your app.
The rest of it
When you want the numbers
The App Rating checker scores any App Store app out of 100 against the leaders in its own category. Free, no account, no card.
ASO Studio