Despite the recent mainstreaming of sustainable investing, it stays questionable whether investments in the sustainability context contribute to a better world. However, for critical topics of impact measurement such as the life cycle, magnitude, and tradeoffs of impact, academic research is still in its infancy. Furthermore, existing approaches in practice do not provide a coherent solution for companies and investors for how to tackle them. We aim to contribute to these discussions by proposing 18 principles for measuring and assessing the life cycle, magnitude, and tradeoffs of impact investments. As such, this white paper is a work in progress and is meant to stimulate discussion, thinking, and developments. Overall, we hope that this paper starts a journey towards adopting a standard to measure the impact of impact investments.