The United Nations' Sustainable Development Goals (SDG) form potentially a great communications framework for financial institutions to report on their indirect environmental sustainability performance. To date, however, no serious effort has been made to specifically assess a financial institution's indirect impact - its impact through the balance-sheets - in terms of the SDGs. Therefore, this thesis sets out to address the following objective: To introduce a prototype system, also referred to as a tool, which is capable of incorporating components of the SDGs so that they may form the criteria based on which financial institutions’ core business activity, their balance-sheets, can be assessed in terms of environmental sustainability. The result of this thesis is a prototype tool programmed in Microsoft's VBA language, aimed to fulfill this objective.