The Last Planner® system (LPS) is used on construction projects to improve the reliability of production planning. A significant process of the LPS is Lookahead planning where activities are broken down into the level of operations, constraints are identified, responsibilities are assigned, and assignments are made ready. The success of Lookahead planning depends on task anticipation, which is a result of activity breakdown and design of operations, and making activities ready by removing constraints. The purpose of this paper is to show through computer simulation the relationship between improving task anticipated (TA) and the reliability of weekly work planning expressed as percent plan complete (PPC). The paper presents a simulation model for the lookahead planning process starting three weeks before execution and ending in activities executed during the work week. The study findings indicate a positive correlation between TA and PPC where improving lookahead planning can increase reliable work execution.