The design of thickness of the flexible pavement has taken the backbone place in determining the overall performance and providing high level of serviceability of the pavement structure for the heavy traffic loads under the adverse climatic conditions, during the expected design period. In Ethiopia there is no software package for flexible pavement design and life cycle cost determination. And it is not common to use software-based design of flexible pavements rather the design agencies practice the manual method. It is quite very difficult to achieve efficiency and reliability using manual work. The pavement design procedure by American Association of State Highway and Transportation Officials (AASHTO) using nomographs could be inconsistent as different results could be obtained by different users for the same input parameters. This research aims to provide a software package for flexible pavement design using Ethiopian Roads Authority (ERA, 2013) and American Association of State Highway and Transportation Officials (AASHTO, 1993) design methods by develop Flexible Pavement Software (FPS). The software determines the layer thicknesses of flexible pavement structure using both Ethiopian Roads Authority (ERA, 2013) and American Association of State Highway and Transportation Officials (AASHTO, 1993) methods. It also determines the life cycle cost of the project based on Net Present Value (NPV) method. The software was validated and the results obtained were found absolutely accurate. Flexible Pavement Software (FPS) is very important as it makes the design process very easy, accurate and saves a lot of precious time and cost, and determines the life cycle cost of the project. Also, increase the value to client by delivering more design alternatives in less time. So, the application of this software will be of great help by avoiding the precision errors that could result in a conservative design or an under design.