ABSTRACT DIII Informatic Engineering of mathematic and science faculty is one of the program study at Sebelas Maret University of Surakarta. The cost of activity must be organized to budget their activities. However, no every cost proposal list can be agreeable, therefore it must be made a decision suitable for the determining the target budget by estimate gotten. To support decision making cost allocation by estimate gotten so needed a decision support system. The program was developed by creating data flow diagram and entity relationalship diagram. The languages use is PHP and editing used Macromedia Dreamweaver. This system can support decision of cost allocation, so decision maker can considere the decision from this system. Keyword: DSS, PHP, cost allocation