The matter of external effects is already well analysed and discussed in various disciplines: welfare, environmental or regional economics analyse the (un)desired externalities in different contexts. However, a suitable comprehensive approach to measure positive external effects induced by concrete urban development projects is still missing. The main focus of the paper thus concentrates on positive external effects of real estate developments from the point of view of public authorities. Real estate developments are defined as brownfield redevelopment projects in integrated urban areas, taking the whole life cycle from site clean-up to infrastructure and building construction and maintenance as a basis. A crucial aspect of this kind of capital intensive projects is obviously financing. Public money is often involved in these projects because of long-term welfare aspects, especially in terms of social stability and economic development in the private and in the public sector. One of the main interests in the process of decision-making is the justification to grant public subsidies. This aspect becomes more and more challenging against the background of the massive limitation of public or rather municipal budgets. A resilient support for decision-making demands a sophisticated analysis of external effects that aim at a strict quantification of the significant aspects. In the first place, this leads to a systematic categorisation of the topical fields of effects considering the person or groups concerned as well as the manifestation in terms of spatial and temporal range. The approach of the paper is to improve the available methods for quantifying positive external effects of real estate development. Therefore, a pattern will be presented that build the basis for the quantitative coverage and prognosis of these effects in the context or urban and regional development. The prospective target is the integration of this methodology in urban and regional planning processes.