The most crucial stage of a project is the construction planning phase. Planning should be done during the planning phase with reference to the number of personnel, supplies, equipment, etc. PERT analysis and the Critical Path Method are two tools used by construction planners to shorten project durations. There is a trade-off between time and cost since project costs rise as project length decreases. Using less costly resources on non-critical tasks can lower the project's overall cost using CPM. Construction managers might utilise it in the planning stage to investigate a multitude of alternatives available to the contractor and forecast the impact of a choice on construction in order to support a preferred operating policy given various management objectives. The study compares the outcomes of the three methods that are employed to accomplish time-cost optimisation. The two methodologies employed were the Linear Programming Method (LP) and the Critical Path Method-Project Crashing Method. A case study, the building of a water treatment plant was taken into consideration in order to compare the outcomes. Thus, the following is presented in this paper: 1) Utilising the Project Crashing Approach. 2) Using Linear Programming (LP).