Background: the Portfolio-To-Impact (P2I) model is a novel financial model, developed to estimate minimum funding needs to accelerate health product development from late stage preclinical study to phase III clinical trials, and to visualize potential product launches over time (from 2017 to 2040). Methods: The assumptions on development costs at each phase were based on clinical trial costs from Parexel’s research and development (R&D) cost sourcebook. These were further refined and validated by interviews, with a wide variety of stakeholders from Product Development Partnerships, biopharmaceutical and diagnostic companies, and major funders of global health R&D. Results: the tool was used to create seven scenarios describing the impact, in terms of products developed, with different product portfolios of funding ranging from $1 million per annum through to $500 million per annum. These scenarios have been previously presented in a report setting out the potential for a new fund for research and development which would assist in accelerating product development for the diseases of poverty. Conclusion: this article describes the assumptions and methods used in developing the P2I modelling tool. The model is published as open access accompanied with a user guide. The design allows it to be adapted and used for other health R&D portfolio analysis as described in an accompanying publication focussing on the pipeline for neglected diseases in 2017. We aim to continually refine and improve the model and we ask users to provide us with their own inputs that can help us update key parameters and assumptions. We hope to catalyse users to adapt the model in ways that can increase its value, accuracy, and applications.