The transmittance spectrum of halftone prints on paper is predicted thanks to a model inspired by the Yule-Nielsen modified spectral Neugebauer model used for reflectance predictions. This model is well adapted for semi-opaque printing supports and applicable to duplex prints. Model parameters are obtained by a few transmittance measurements on calibration patches printed at one side of the paper. The model was verified with duplex specimens printed by inkjet with standard and custom inks, at different halftone frequencies and on various types of paper. Predictions are as accurate as those obtained with a previously developed reflectance and transmittance prediction model relying on the multiple reflections of light between the paper and the printair interfaces.