Community health worker (CHW) programmes are currently being scaled-up in sub-Saharan Africa to improve access to healthcare. CHWs are often volunteers; from an economic perspective, this raises considerations whether reliance on an unpaid workforce is sustainable and how to appropriately cost and value the work of CHWs. Both these questions can be informed by an understanding of CHWs’ workload, their opportunity costs of time and the perceived benefits of being a CHW. However, to date few studies have fully explored the methodological challenges in valuing CHW time. We examined the costs and benefits of volunteering in a sample of 45 CHWs providing integrated community case management of common childhood illnesses in rural Uganda in February 2012 using different methods. We assessed the value of CHW time using the minimum public sector salary rate and a CHW-elicited replacement wage, as well as the opportunity cost of time based on CHW-estimated annual income and alternative work opportunities, respectively. Reported monthly CHW workload, a median of 19.3 h (range 2.5–57), was valued at USD 6.9 (range 0.9–20.4) per month from the perspective of the healthcare system (applicable replacement wage) and at a median of USD 4.1 (range 0.4–169) from the perspective of the CHWs (individual opportunity cost of time). In a discrete choice experiment on preferred work characteristics, remuneration and community appreciation dominated. We find that volunteering CHWs value the opportunity to make a social contribution, but the decision to volunteer is also influenced by anticipated future rewards. Care must be taken by those costing and designing CHW programmes to acknowledge the opportunity cost of CHWs at the margin and over the long term. Failure to properly consider these issues may lead to cost estimations below the amount necessary to scale up and sustain programmes.