A well-known practice to accelerate construction projects is to overlap the design phase activities. For a typical construction project, a number of overlapping strategies exist during the design phase which all can result in timesaving. However, the cost of these strategies varies significantly depending on the total rework and complexity they generate. A favorable overlapping strategy is one that generates the required timesaving at the minimum cost. To find such a strategy, the question "Which activities have to be overlapped and to what extent to reduce the project duration at the minimum cost?" should be answered. This research aimed at answering the question through generating an overlapping optimization algorithm. The algorithm works based on the principles of genetic algorithms (GAs). The algorithm explained in the paper is unique compared to previous algorithms and frameworks available in the literature, as it can optimize multi-path networks and can handle all types of activity dependencies (i.e. finish-to-start, start-to-start, and finish-to-finish). It also takes both critical and non-critical activities into account and follows the critical path if the critical path changes or new critical paths emerge. A computer tool was also developed to run, examine and validate the overlapping optimization algorithm. This paper introduces the algorithm and the computer tool in detail and explains the results of their validation through optimizing a real-world project schedule. (C) 2015 Elsevier B.V. All rights reserved.