Calculating the average rating for each category in a Laravel application can be done using Eloquent's `avg` method on a relation. This can be achieved by retrieving all categories and their associated products, then calculating the average rating for each category. For example: `$category = Category::with('products')->get(); $averageRating = $category->products()->avg('rating');`. To calculate averages across multiple related models, use the `withAverage` method provided by Laravel.