A new semi-empirical model of phase equilibria of hydride forming metals and alloys with hydrogen gas (PCT diagrams) has been developed. Within the model, pressure composition isotherms (PCI's) for hydrogen absorption and desorption are presented as pseudo convolutions of one core function, or "ideal" PCI built according to Lacher model, or model of Van der Waals lattice gas, with two modified asymmetric pseudo Voight distribution functions. The median of the absorption distribution is shifted from the one of the desorption distribution towards higher pressures, by the value related to a minimum of a hysteresis free energy (assumed to be constant) and an excessive chemical potential of hydrogen in over-saturated alpha-solid solution. The model allows to simultaneously fit both H-2 absorption and desorption datasets and adequately simulates the features of experimental PCT diagrams in wide temperature range including (i) presence of several plateau segments, (ii) hysteresis including its disappearance when approaching to critical temperature, (iii) shape of transitions between alpha-, (alpha + beta)- and beta-regions, and (iv) flat or sloping plateaux including temperature and concentration dependencies of the plateau slope. The article also presents a demonstration software (macro-enabled Excel workbook with an ActiveX calculation module) for the fitting of experimental PCT datasets verified on the systems H-2 - LaNis-xSnx, H-2 - TiFe and H-2 - bcc-V(Ti,M); M = Zr,Ni. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.