Master Production Schedule (MPS)

Creating an MPS starts with demand input — a combination of firm customer orders, sales forecasts, safety stock requirements, and distribution center replenishment needs. The planner converts this demand into a time-phased production plan, respecting several constraints: available capacity (from rough-cut capacity planning), material availability (from MRP), existing inventory and WIP, minimum batch sizes, and frozen scheduling zones. The MPS typically has three zones: a frozen zone (usually 1–4 weeks) where the schedule is locked to provide stability for material procurement and shop floor execution; a slushy zone (4–8 weeks) where changes are possible with management approval; and a liquid zone (beyond 8 weeks) where the schedule is flexible and driven primarily by forecasts. This zoning structure prevents the constant replanning that destroys manufacturing efficiency while maintaining responsiveness to demand changes further out. The MPS should be reviewed and updated weekly, comparing actual demand against forecast and adjusting future periods accordingly.

While the MPS concept originated in the MRP/ERP era of batch-and-queue manufacturing, it remains highly relevant in modern lean and agile environments. The key evolution is in time bucket granularity and update frequency. Traditional MPS used weekly or monthly buckets updated monthly. Modern practice uses daily or even shift-level buckets (as supported by tools like LinePlanner) updated weekly or more frequently. This finer granularity aligns the MPS with lean principles like heijunka (production leveling) and enables tighter synchronization between the plan and actual shop floor conditions. In a LinePlanner-based workflow, the MPS function is served by the production calendar itself: planners place orders on specific days and shifts across production lines, the visual layout immediately reveals capacity conflicts, and drag-and-drop interaction makes schedule adjustments intuitive. The calendar becomes both the planning tool and the communication medium, eliminating the gap between the MPS (what we plan) and the dispatch list (what we do).

Several common pitfalls undermine MPS effectiveness. Overloading occurs when the MPS exceeds actual capacity, leading to chronic late deliveries and expediting. This happens when planners schedule to theoretical (not demonstrated) capacity or when sales makes commitments without checking the MPS. Under-loading wastes capacity by being too conservative, often driven by planners who pad the schedule to avoid risk. Nervous scheduling results from too-frequent changes to the frozen zone, destabilizing material procurement and shop floor plans. Disconnect from demand happens when the MPS is based on outdated forecasts rather than current order data. Ignoring constraints means the MPS looks feasible on paper but fails in execution because it ignores tooling limitations, material lead times, or workforce skills. The remedy for all these pitfalls is a disciplined Sales and Operations Planning (S&OP) process that aligns demand, supply, and financial plans monthly, combined with a weekly MPS review that makes data-driven adjustments within the established framework.