An implantable cardioverter defibrillator (ICD) has a programmable ICD energy level corresponding to the maximum defibrillation energy deliverable with each defibrillation shock pulse. The ICD energy level is programmable within the maximum energy capacity of the defibrillation capacitor(s) of the ICD. In various embodiments, after a user enters the ICD energy level, one or more corresponding ICD performance parameters are presented. Restrictions are applied to the energy level programming of the ICD to ensure the predictability of the one or more ICD performance parameters.