The importance of expressing composition of used catalysts in fresh basis is highlighted in this work. Since catalysts are subject to changes during processing, e.g. coking and metal deposition, their composition varies depending on their state (fresh, spent, regenerated) and to properly determine catalyst life, composition needs to be changed to fresh-basis. Previous works are commented to demonstrate the current confusion existing in the literature when reporting metal content of used catalyst, and a simple approach is developed to change catalyst metal composition to fresh-basis. (C) 2009 Published by Elsevier Ltd.