This paper presents a new approach to cost analysis of family planning programmes that focuses on behaviour change of programme clients as the final ‘output’ rather than units of contraceptive services delivered, as does the familiar couple-years-of-protection index. It is useful to know how much it costs to deliver a unit of contraceptive services, but it would also seem useful to know how much it costs to change a prospective client’s behaviour. The proposed approach rests on the familiar ‘steps to behaviour change’ paradigm and: (1) develops a methodology for applying a client-behaviour-change-centred cost analysis to programme activities; (2) tests the methodology and concepts by applying them retrospectively to a case study of mass media interventions in Egypt; (3) derives cost per unit of behaviour changes for these Egyptian communications campaigns to demonstrate the workability of the approach. This framework offers a new approach to impact evaluation that would seem to be applicable to other components of family planning and reproductive health programmes.