The present invention extends to methods, systems, and computer program products for calculating zoom level timeline data. Event aggregators are configured to read execution data from sequentially received input buffers and pre-calculate data chunks for a specified zoom level to create a zoom tree. The density of execution data can be used to determine when pre-calculation is beneficial. In response to a user request, pre-calculated data can be combined with responsively calculated data for presentation to a user. User requests can specify zoom levels and time ranges over which data is to be presented.