Population ageing is rising in the twenty-first century, and most will live in urban areas. Thus, planning an age-friendly city is paramount as a primary driver of quality of life, putting up the challenge of adjusting urban structures and public space to promote active and healthy ageing. Furthermore, such approach must consider the present and future context of climate change. The role of the outdoor built environment and public infrastructure in the ageing process is crucial and can therefore influence older people’s mobility, independence, and overall quality of life. Although the delineation of age-friendly environments has been proposed since the beginning of this century, the current challenge is to measure how age-friendly cities are due to age-friendly effective planning or its absence. In this sense, there have been some approaches to creating age-friendliness indices, mainly focused on the spatial determinants of an age-friendly environment. However, these indices still reflect a gap in integrating ageing communities’ perceptions and social needs as drivers of age-friendliness. That said, taking the city of Lisbon, Portugal, as a case study, we propose a methodological approach to creating an Age-Friendly Neighbourhood Index in a Changing Climate.