Better measures of productivity are needed to support software process improvements. We propose and evaluate indicators of productivity trends that are based on the premise that productivity is closely related to the effort required to complete change tasks. Three indicators use change management data, while a fourth compares effort estimates of benchmarking tasks. We evaluated the indicators using data from 18 months of evolution in two commercial software projects. The productivity trend in the two projects had opposite directions according to the indicators. The evaluation showed that productivity trends can be quantified with little measurement overhead. We expect the methodology to be a step towards making quantitative self-assessment practices feasible even in low ceremony projects.