Although fintech and collaborative funding platforms have evolved into sophisticated information and interaction systems, it is still complex to measure their social impact, especially when it comes to public value-driven platforms such as civic crowdfunding. Addressing this problematic question, at both, the conceptual and technical level, in this article we present a novel dynamic system framework and implementation for assessing the social impact of crowdfunding campaigns through the Goteo.org platform. Our contribution derives from an interdisciplinary team effort led by the non-profit Platoniq Foundation (founder and main promoter of the Goteo platform) in which social researchers and software developers worked together in order to improve the accuracy and visibility of crowdfunding campaigns in relation to their social impact. This approach for calculating and visualizing social impact, as a proof-of-concept, is based on a methodological framework inspired by previous advancements in the non-profit and social responsibility sectors, integrating both, user-generated data and external data sources and indicators. As a recently launched system, in its current implementation on Goteo it integrates the first version of a virtual calculator embedded in the campaign design interface. This new digital affordance allows project promoters to better estimate monetary and non-monetary-related impact regarding social value, public return of investment and other specific concepts related to their crowdfunding campaign and the derived project. Results of this social impact calculator, which translates diverse value variables into economic estimations, is also made visible to all users as potential campaign donors, and operates in connection with previously implemented SDGs indicators and social, democratic and ecological footprints in Goteo.