Understanding animal home ranges and other patterns of space utilisation is an important component of spatial ecology. It allows researchers to explore and explain site occupation and habitat preferences, and also interaction and avoidance behaviour. Conventional analyses of animal home ranges use points at which the animals are observed, sometimes weighted by the time difference between sequential observations. This creates an issue in that the analysis can assign undue weight to a sample point with a long time delay from the previous observation, as the full path from the preceding point is implicitly assigned to that point. Conventional analyses also do not take into account physical constraints such as boundaries (e.g. rivers, roads, cliffs) or the cost of traversing alternate possible paths between points, typically inferring a straight-line path between sequential samples. This conventional approach has obvious limitations, especially in constrained environments such as for fish in rivers and estuaries. These limitations can be attributed in large part to a lack of available software tools.In this paper we describe a software tool we have developed that calculates kernel density estimates of occupation times by using the per-segment transit times along a path inferred using a cost surface that is constrained to remain between defined boundaries. To illustrate the functionality of the tool we use a data set of Argyrosomus japonicus (Mulloway) movements, an estuarine fish species, sampled from the Georges River estuary in Sydney, NSW. The approach is, however, generic and can be applied to any environment where animal movements are constrained, for example fragmented agricultural landscapes. The tool is written using the ESRI arcpy system, but is open source so can readily be ported to other GIS software packages.