Systems, methods, and software can be used to determine a confidence value for a fracture plane. In some aspects, a subset of microseismic events associated with a fracture treatment of a subterranean zone are selected. Confidence in associating the selected subset of microseismic events with a common fracture plane is determined. The confidence can be determined, for example, based on the number of microseismic events in the subset, a location uncertainty for each microseismic event in the subset, a moment magnitude for each microseismic event in the subset, a distance between each microseismic event and a fracture plane fitted to the microseismic events, an orientation of the fracture plane fitted to the microseismic events, or a combination of these and other factors.