This article provides evidence-based guidance for practical survey work, namely choosing interviewers and their workload. Analyzing a survey of 3,568 households obtained through computer assisted personal interviews (CAPI), we find that interviewers learn considerably while the survey progresses. Time requirements for fieldwork increase concavely with sample size. This allows using larger samples with a given budget than would be expected in planning such projects with simplistic cost estimates. We find a decrease of interview duration of almost 50%, which translates into a significant increase of the average hourly wage the interviewers receive. These learning effects cease after around 20 interviews. Based on our results, we recommend targeting interviewer training by age and technology-affinity of interviewers for CAPI surveys.