Starting from the results of a recent ion-molecule reactive scattering experiment [Tosi et al., J. Chem. Phys. 100, 4300 (1994)], a precise estimate of the upper bound for the heat of formation of NH+ has been derived [Delta H-f,H-0(NH+) less than or equal to 17.175 +/- 0.006 eV], and from this, upper and lower bounds for the heat of formation of NH and for the dissociation energies of NH+ (X (2) Pi and a (4) Sigma(-) states) and NH (X (3) Sigma(-)), respectively, In order to verify the degree of accuracy attainable on the theoretical counterpart for these systems, high level ab initio computations, using extended multireference configuration interaction expansion and recently developed core-valence correlation consistent basis sets [Woon et al., J. Chem. Phys. 103, 4572 (1995)], have been also performed, comparing the results with the corresponding values estimated from the experimental data and previous theoretical literature values.