Post-tensioned (PT) flat slabs are a commonly used construction system in multi-story buildings worldwide. This is due to time saving caused by early removal of formwork, as well as overall cost saving compared to traditional reinforced concrete flat slabs. Design of PT slabs can be accomplished using approximate methods presented by different codes of practice, which can only be applied for slabs with regular column arrangement. However, irregular structures with complex geometries need to be analyzed using different analytical approaches such as finite element method (FEM). Several commercial programs are used to analyze and design the PT flat slabs, which do not necessarily produce identical results. “SAP2000"[1], “SAFE"[2], “RAM Concept"[3] and “ADAPT Builder"[4] are examples of commercial programs used in the design of the PT flat slabs. Different layouts of the prestressing tendons in two orthogonal directions are used in construction of flat slab system; these such as[5]: Distributed/Distributed, Distributed/Banded, Banded/Distributed and Banded/Banded. Choice of distributions and layout of the tendons in the flat slab system differ according to the designer vision and experience. In this research, the design of post tensioned flat slabs is explored. The finite element programs used to design the PT slabs are evaluated and the efficiency of the different post tensioning patterns are studied. Design tables giving the recommended post tensioning rate for different spans, loadings and span-to-depth ratios are given. Finally, the economic advantage of posttensioned over conventional reinforced concrete slabs is presented.