A detailed crystal-field splitting analysis is given for the 26 lowest-energy multiplet manifolds, 2S+1LJ, of Nd3+ (4f3) in polycrystalline ceramic garnet Y3Al5O12 (YAG). The absorption spectra obtained between 8 K and room temperature, and between 1750 and 350 nm, and the fluorescence spectrum obtained at 8 K and observed between 1450 and 875 nm are analyzed for transitions between individual energy (Stark) levels that characterize the energy-level structure of Nd3+ ions in D2 symmetry sites, replacing Y3+ ions in the garnet host lattice. A model Hamiltonian including atomic and crystal-field terms is diagonalized within the complete 4f3 SLJMJ basis set which includes 364 states. The calculated splitting of the Nd3+ energy levels by the crystal field is compared with the experimental splitting observed in both the ceramic sample and a single-crystal laser rod. Both samples have approximately the same Nd3+ concentration, about 1 at. %. By varying the atomic and crystal-field parameters, we obtain a standard deviation of 18 cm-1 between 106 calculated-to-observed Stark levels found between the ground state and the 4D1/2 at 28 369- 2002;cm-1. Within this standard deviation the energy-level structure of Nd3+ is found to be similar in both samples. Low temperature visible and near IR spectra of ceramic Nd3+:YAG show it has comparable properties to the crystalline analog.