The fast-ion phase-space coverage of the ASDEX Upgrade Fast-Ion Loss Detectors (FILD) has been estimated and the results are presented here. To that end, a numerical tool has been developed to determine particle orbits that can be accepted by each detector in the machine, depending on their radial position, without colliding to the first wall. Two different plasma shapes have been analyzed and results show excellent phase-space coverage for mostly all the detectors, especially for those located at the midplane and below it. The methodology developed provides an excellent way to estimate the signal of these detectors depending on the plasma scenario and can be easily extended to other machines. Also, this study can be complemented with thermal analysis to consider the structural integrity of the detectors, allowing determining optimal operation parameters both from the signal and safety standpoints.