Here at chalkdust HQ one of our philosophies is that mathematical thinking and reasoning can be applied to all walks of life. For example, in our first issue we had an interview with Dr Hannah Fry, who discussed the mathematics of love. In this blog post, I’m going to talk about a growing movement of people applying mathematical reasoning to another area of life that is often considered emotional: donating money to charity. This group of people, called “effective altruists”, believe that choosing which charity we donate money to shouldn’t be an entirely emotional decision, dictated by which organisation can best tug at your heartstrings. Instead we should be guided by evidence and find a way of rationally measuring which charities do the most good.