A quartz crystal microbalance with dissipation, or QCM-D, allows the properties of a loaded quartz oscillator—resonance frequency and dissipation [1/(the quality factor)]—to be monitored on several overtones. The frequency and the dissipation factor of the loaded oscillator are functions of the physical properties (such as thickness, density, viscosity, elasticity, roughness) of the media loading the resonator (e.g., a liquid, a thin polymer film, a phospholipid bilayer, etc.) and the frequency at which the measurement was performed. In this contribution, it is shown that the frequencies measured with the QCM-D instrument on the first, third, fifth, and seventh overtones do not agree with those expected of an ideal, infinite crystal. Therefore, the results of QCM-D measurements cannot be directly compared with theoretical models that require the resonance frequency of an unloaded crystal to be used as one of the input parameters. A phenomenological procedure for dealing with this problem is proposed.