Waller–Hartree calculations of molecular incoherent scattering factors S( μ) for CH4, NH3, and H2O are reported to provide an unambiguous comparison with recent calculations of S( μ) for these molecules made by integration of impulse approximation Compton profiles. It is found that the latter approach leads to both qualitative and quantitative errors at small momentum transfer μ. Moreover, it is pointed out that Waller–Hartree calculations of S( μ) require very little additional effort when one is calculating elastic cross sections. An illustrative calculation for diborane is used to suggest that even self-consistent field calculations of the Waller–Hartree S( μ) can be useful in the analysis of experimental data provided that some caution is used and that the calculations are approximately corrected for electron correlation effects.