Check where the advertised ingredient sits on the ingredient list

Ingredients are listed in descending order only until you get to about 1%. Below that, they can appear in any order.

So the useful thing is not just whether an active is near the end. Look at what it is sitting next to.

If the hero ingredient is listed around or below things that are usually used under 1%, like phenoxyethanol, fragrance, disodium EDTA, xanthan gum, sodium benzoate, or tocopherol, then it is probably in that sub-1% part of the formula.

That still does not automatically mean it is useless. Retinoids, peptides, and some branded actives can work at low concentrations or be used at the supplier's intended level.

Basically, the ingredient list can tell you the order and sometimes help you spot the 1% zone. It cannot tell you the exact percentage.

Worth checking before assuming the ingredient printed on the front is doing most of the work.