In this talk I will outline how to compute the decay spectrum for dark matter with masses above the scale of electroweak symmetry breaking, all the way to the Planck scale. These spectra are a crucial ingredient in the search for dark matter via indirect detection at the highest energies as being probed in current and upcoming experiments including IceCube, HAWC, CTA, and LHAASO. The method described improves considerably on existing approaches. For example, I will outline how to include all relevant electroweak interactions. The importance of these effects grow with dark matter mass, and by an EeV the spectra can differ by orders of magnitude from existing results.