The ATLAS level-1 calorimeter trigger is a hardware-based system that identifies events containing calorimeter-based physics objects, including electrons, photons, taus, jets, and missing transverse energy. In preparation for Run 3, when the LHC will run at higher energy and instantaneous luminosity, the level-1 calorimeter trigger is currently implementing a significant program of planned upgrades. The existing hardware will be replaced by a new system of feature extractor modules, which will process finer-granularity information from the calorimeters and execute more sophisticated algorithms to identify physics objects; these upgrades will permit better performance in a challenging high-luminosity and high-pileup environment. The features of the upgraded level-1 calorimeter trigger and the plans for production, installation, and commissioning will be described and in addition, the expected performance of the system in Run 3 will be discussed.