Purpose: The purpose of this paper is to present a mathematical model that can be used as an educational tool to reflect the philosophical aspects of sustainability. Design/methodology/approach: This is a descriptive paper. Findings: Everyone carries a sustainability deficit. Therefore, opportunities to reduce this deficit abound. Education is an excellent vehicle to achieve sustainability. Practical implications: Helping individuals with extremely high sustainability deficit to make minimum improvements is more beneficial than a further reduction of the "deficit" by those who have it already low. Further action is certainly encouraged, especially to quantify the sustainability index. Originality/value: The paper fulfils the need of providing an original model upon which educators may lean to, in order to enhance learning in sustainability. (Contains 1 figure.)