CARI-6 is the sixth major release of galactic cosmic radiation (GCR) dose calculation software developed by the U.S. Federal Aviation Administration (FAA). The software is of benefit to the FAA and the public as a tool used by scientists investigating health effects of ionizing radiation in the atmosphere. It provides GCR dose estimates for past flights and also serves as a verified radiation monitoring tool to aid the aviation industry and individuals in their radiation protection programs. Compiled versions of the software are available from the Radiobiology Research Team Website. The source code is available upon request.