This paper examines the feasibility of incremental annotation, i.e. using existing annotation on a text as the basis for further annotation rather than starting the new annotation from scratch. It contains a theoretical component, describing basic methodology and potential obstacles, as well as a practical component, describing an experiment which tests the efficiency of incremental annotation. Apart from guidelines for the execution of such pilot experiments, the experiment demonstrates that incremental annotation is most effective when supported by thorough pre-planning and documentation. Unplanned, opportunistic use of existing annotation is much less effective in its reduction of annotation time and furthermore increases the development time of the annotation software, so that this type of incremental annotation appears only practical for large amounts of heritage data.