Get current category ID of the active page

If it is a category page,you can get id of current category by:

$category = get_category( get_query_var( 'cat' ) );
$cat_id = $category->cat_ID;

If you want to get category id of any particular category on any page, try using :

$category_id = get_cat_ID('Category Name');

You can try using get_the_category():

$categories = get_the_category();
$category_id = $categories[0]->cat_ID;

The oldest but fastest way you can use is:

$cat_id = get_query_var('cat');

I use the get_queried_object function to get the current category on a category.php template page.

$current_category = get_queried_object();

Jordan Eldredge is right, get_the_category is not suitable here.

I think some of the above may work but using the get_the_category function seems tricky and may give unexpected results.

I think the most direct and simple way to access the cat ID in a category page is:

$wp_query->query_vars['cat']

Cheers