This paper introduces an exact schedulability analysis for the optional computation model urider a specified failure hypothesis. From this analysis, we propose a solutionfor determining, before run-time, the degree of fault tolerance allowed in the system. This analysis will allow the system designer to verifL fall the tasks in the system meet their deadlines and to decide which optional parts must be discarded if some deadlines would be missed. The identification of feasible options that satisfL some optimality criteria requires the exploration of a potentially large combinatorialspace of possible optional parts to discard. Since this complexity is too high to be considered practical in dynamic systems, two heuristic algorithms are proposedfor selecting which tasks must be discarded and for guiding the process of searching for feasible options. The performance of the algorithms is measured quantitatively with simulations using synthetic tasks sets.