Efficient analysis methods are needed for the effective optimisation of the preliminary structural design of, e.g., aircraft and space vehicles. In cases advanced materials such as laminated composites made of fibre-reinforced-plastics are used, the transverse shear deformation is not negligible if the laminates possess little transverse shear stiffness or are considered “thick”. Therefore, the classical laminated plate theory (CLPT) is not sufficient and higher-order shear deformation theories should be applied. While there are closed-form computational models for the postbuckling analysis based on the CLPT, there is a lack of models developed for shear deformable laminates. Thus, a new computational model is introduced. The analysis method is based on high-order shear deformation theories and is derived based on the principle of the minimum of the total elastic potential. The results are discussed in comparison with finite element analyses. The promising results of the approximate computational model offer the possibility to fully exploit the optimisation potential.