APS Calculations

How to Calculate APS Scheduling Metrics: Finite Capacity, Load Balance, and Dispatch Priority

Step-by-step formulas for the calculations that drive an APS engine, from finite capacity load percentage to dispatch priority and schedule stability, with real units and worked examples.

Advanced planning and scheduling math starts with finite capacity load, the percentage of a work center's available time that the current plan consumes. The formula is Load % = (sum of required run time plus setup time) divided by net available capacity, times 100. If a CNC cell has 3 machines running two 8 hour shifts at 85% availability, net capacity is 3 times 16 times 0.85 equals 40.8 machine hours per day. Load 2,040 minutes of run time plus 360 minutes of setup, that is 2,400 minutes or 40 hours, so load is 40 divided by 40.8 equals 98%. Use the Finite Capacity Load calculator to confirm you are not scheduling past 100%.

Machine load balance measures how evenly demand spreads across parallel resources, which drives throughput more than raw capacity. Compute the coefficient of variation: standard deviation of load hours across machines divided by the mean. Suppose four presses carry 30, 42, 18, and 30 hours. Mean is 30, standard deviation is about 8.49, so CV is 0.283 or 28.3%. World-class balance sits under 10%. Every point of imbalance leaves the lightly loaded machine idle while the heavy one queues. The Machine Load Balance calculator turns those numbers into a rebalanced assignment so no single resource exceeds the mean by more than 15%.

Dispatch priority decides what runs next when a queue holds more jobs than capacity. A common composite score weights three inputs: critical ratio, slack, and setup similarity. Critical ratio equals time remaining until due date divided by total remaining work time. A job due in 20 hours with 25 hours of work has a CR of 0.80, which is under 1.0 and therefore already behind. Slack equals due date minus (now plus remaining processing), so a job due at hour 40 with 12 hours of work at hour 20 has 8 hours of slack. The Dispatch Priority Score calculator combines these into a single sortable number per job.

Changeover sequencing math finds the cheapest order to run a set of jobs when setup time depends on the transition. Build a changeover matrix in minutes: changing color A to B might cost 45 minutes, B to A 20 minutes, A to C 15 minutes. For 6 jobs, total setup under a poor sequence might be 210 minutes versus 95 minutes under an optimized one, a 115 minute recovery per cycle. At a loaded machine rate of 140 dollars per hour that is 268 dollars saved each time the sequence repeats. The Changeover Sequence Savings calculator ranks permutations so you run families back to back.

Bottleneck impact links a single constraint to whole line output using the theory of constraints identity: system throughput equals bottleneck throughput. If the constraint runs at 92 parts per hour and the plan demands 100, the schedule is infeasible by 8 parts per hour regardless of upstream speed. Multiply the shortfall by shift hours to size the gap: 8 times 16 equals 128 parts short per day. Elevating the bottleneck by 5 parts per hour closes most of it. The Bottleneck Schedule Impact calculator propagates a constraint rate change through the full routing to show the true output delta.

Schedule stability quantifies how much a plan churns between planning runs, which matters because every reschedule ripples into material and labor. Stability equals 1 minus (number of jobs whose start time moved divided by total scheduled jobs) inside the frozen window. If 18 of 120 jobs shifted in the daily regen, stability is 1 minus 0.15 equals 0.85, or 85%. Nervousness above 15% inside a 5 day frozen fence usually signals demand or lead time inputs changing faster than the fence protects. The Production Schedule Stability calculator tracks this per run so you can widen the fence with evidence.

Constrained scheduling handles the case where labor or material, not machines, caps output. Labor-constrained load divides required direct labor hours by available crewed hours: 620 required hours against 8 operators times 40 hours equals 320 available means you are short 300 hours and can staff only about 52% of the plan. Material-constrained load compares gross requirements to on-hand plus scheduled receipts inside lead time. The Labor-Constrained Schedule and Material-Constrained Schedule calculators solve for the binding resource first, because scheduling machines you cannot feed or staff produces a plan that fails on day one.

Tie the pieces together with a feasibility check before you commit a schedule. Run finite capacity load to confirm no work center exceeds 100%, load balance to keep CV under 15%, then constrained checks for labor and material coverage above 100% of gross requirement. A job set that passes all four is executable. One that shows 98% capacity but only 52% labor coverage is not, and dispatch priority cannot fix it. Sequence the surviving jobs with changeover math, then measure stability across the next three regens to confirm the plan holds before you promise dates to customers.

Published 2026-07-01.