Manufacturing has traditionally prioritised cost, lead times, and quality over sustainability. However, increasing awareness of environmental impact demands greater accountability. The concept of sustainability often lacks clarity, and companies struggle to prioritise environmental goals. This paper presents the development of an end-of-life (EoL) calculator based on selected key performance indicators (KPIs), divided into three areas—economic, environmental, and social—to evaluate EoL options such as disposal, recyclability, and raw material recovery, providing performance scores to support decision-making. This study includes a proof-of-concept case focused on the aviation sector, where non-operational factors contribute significantly to its carbon footprint. Aircraft cabin components, making up 10% of an airliner’s empty weight and replaced multiple times during an aircraft’s lifespan, create substantial waste, a significant portion of which is not recycled. To validate the calculator, a Discrete Event Simulation (DES) model of the supply chain was developed to assess the recyclability of aircraft seats. This study highlights the challenges and opportunities of implementing circular economy practices in regulated sectors like aerospace. Despite its limitations, the calculator establishes a practical framework for sustainable decision-making in manufacturing and supply chains.