Self-assessment answers from Module 4
One. The four gates are: Demand Review (output: agreed demand plan), Supply Review (output: agreed supply plan with planned orders and capacity adjustments), Executive S&OP (output: approved plan or identified tradeoffs), and Cycle Lock (output: published, frozen plan).
Two. Sequential gates produce a shorter cycle because they eliminate rework. In a parallel process, supply plans built against a demand number that is still being negotiated have to be rebuilt when the demand number changes. In a sequential process, supply planning starts from a locked demand number and does not have to be rebuilt. The total elapsed time is shorter even though the gates are sequential.
Three. Consensus on the number means everyone agrees the forecast is correct. Consensus to use the number means everyone commits to planning against it, even if they personally believe it is too high or too low. The distinction matters because demanding agreement on the number leads to endless negotiation, while demanding commitment to use the number forces the discussion to focus on specific override reasons rather than overall level.
Four. S&OP drift is the practice of quietly editing the published plan after sign-off, usually by a team that disagreed with the consensus but did not raise it in the meeting. The cycle lock prevents it by freezing the plan at the system level once the executive gate approves it, making post-lock edits impossible or requiring a documented exception with executive approval.
Five. S&OP software must do two things to reduce cycle time: enforce a single source of truth at the data model level (one demand number, one supply number, one inventory number, all from the same dataset), and enforce sequential gates at the workflow level (supply review cannot start until demand is locked, executive S&OP cannot start until supply is locked). Most software fails because it provides collaborative tools without changing the architecture, so the reconciliation work remains.
If you got all five, continue.
What this module covers
This module covers the supply side of planning. Once the S&OP cycle has produced a locked demand plan (Module 4), the supply planning function must determine what to make, what to buy, and what to stock. This module covers supply netting (the computation that turns demand into replenishment requirements), safety stock (the buffer that protects against uncertainty), reorder points (the trigger for replenishment), and gap analysis (the identification of supply shortfalls before they become stockouts).
Supply netting: the core computation
Supply netting is the computation that determines net supply requirements. The formula is simple: net supply requirement equals demand minus existing supply. Existing supply includes current inventory, open purchase orders, and scheduled production. If demand for a SKU in a given period is 1,000 units, and you have 600 units in inventory plus 200 units on order, the net supply requirement is 200 units.
The computation is done per SKU, per location, per period. For a manufacturer with 5,000 SKUs across 12 locations and 13 weekly periods, that is 780,000 individual netting calculations. This is why it must be automated. Manual netting in spreadsheets is feasible for a few hundred SKUs but breaks at scale.
The critical operational property of supply netting is idempotency. Running the netting computation twice should produce the same result as running it once. If you re-run netting after a demand update, the previous planned orders should be updated in place, not duplicated. Non-idempotent netting produces a growing mess of duplicate planned orders that have to be manually reconciled, which defeats the purpose of automation.
Idempotency requires the netting system to identify planned orders by a stable key (typically a combination of SKU, location, and period) and to use upsert (update or insert) semantics rather than append. This is an engineering detail, but it is the engineering detail that determines whether supply netting is usable in practice.
Safety stock: the buffer
Safety stock is the inventory buffer held to protect against demand and lead time uncertainty. Module 3 of this course and the dedicated article on safety stock cover the formulas in depth. This module covers the practical application.
The standard safety stock formula is: safety stock equals the service level factor (Z) multiplied by the standard deviation of demand during lead time. The Z factor comes from the normal distribution: 1.65 for 95% service, 2.33 for 99%. The standard deviation captures demand variability over the replenishment lead time.
The three assumptions that must be checked before applying the formula are: demand is normally distributed (fails for intermittent and lumpy demand), lead time is constant or its variability is measured (often not tracked in ERPs), and the service level definition is clear (cycle service level, fill rate, and ready rate give different targets for the same percentage).
For practical application, segment your SKUs. Apply the full formula, with lead time variability and the correct service level definition, to A-class SKUs (top 20% by revenue or volume). For B-class, use the basic formula with a rough lead time estimate. For C-class, especially slow movers, use days-of-supply targets rather than the formula, because the formula's assumptions break worst on low-volume items.
Recompute safety stock regularly. Demand variability and lead time variability change. A target computed in January may be wrong by June. Schedule quarterly recomputation for A-class, semi-annual for B-class, annual for C-class.
Reorder points: the trigger
The reorder point is the inventory level at which a replenishment order should be placed. The formula combines the expected demand during lead time with the safety stock: reorder point equals average demand during lead time plus safety stock.
If average demand is 100 units per week, lead time is 3 weeks, and safety stock is 150 units, the reorder point is 300 (100 times 3) plus 150, equals 450 units. When inventory drops to 450, a replenishment order is triggered.
The reorder point is the operational link between the planning world (demand plans, safety stock targets) and the execution world (purchase orders, production orders). It is the number that the ERP or inventory system watches to decide when to reorder. If the reorder point is wrong, replenishment happens at the wrong time, and you either stock out or carry excess inventory.
Reorder points should be recomputed whenever safety stock is recomputed, because the reorder point depends on the safety stock. If safety stock increases (because demand variability increased), the reorder point increases. If the ERP still has the old reorder point, replenishment will be triggered too late, and you will stock out.
Gap analysis: finding the shortfalls
Gap analysis is the process of identifying where supply will fall short of demand, before the shortfall becomes a stockout. The computation compares the supply plan (inventory plus open orders plus planned production) against the demand plan, per SKU, per period. Where supply is less than demand, a gap exists.
Gaps should be flagged with severity. A gap of 5% of demand in a period 8 weeks out is a minor warning. A gap of 30% of demand in a period 2 weeks out is critical. The severity scoring tells the supply planning team where to focus.
The operational value of gap analysis is timing. A gap identified 8 weeks before it occurs can be closed by expediting a purchase order, adjusting a production schedule, or negotiating a substitute with the customer. A gap identified 2 weeks before it occurs can only be closed by emergency expedite, which is expensive, or by accepting the stockout, which is costly in a different way.
Automated gap analysis should run after every supply netting computation. The gaps should be surfaced as exceptions, ranked by severity and time-to-impact, and assigned to a planner for resolution. This is the exception-first workflow: instead of reviewing every SKU every cycle, the planner reviews only the SKUs with gaps, which is typically 5-15% of the portfolio.
The connection to the demand plan
Everything in this module depends on the quality of the demand plan from Module 4. Supply netting computes net requirements from the demand plan. Safety stock is calibrated to demand variability. Reorder points are based on demand during lead time. Gap analysis compares supply against demand.
If the demand plan is wrong, the supply plan is wrong. If the demand plan is biased high, you will overstock. If biased low, you will stock out. The accuracy metrics from Module 3 are not just about the forecast. They are about the entire downstream supply chain, because every supply decision is derived from the demand number.
This is why the S&OP cycle (Module 4) matters so much. The cycle is not just a process for agreeing on a number. It is the process that determines the quality of the number that the entire supply chain plans against. A well-run S&OP cycle with sequential gates and a cycle lock produces a demand plan that the supply chain can trust. A poorly run cycle produces a number that everyone knows is wrong, which means the supply plan is built on a foundation of sand.
What to do next
This module covered supply netting, safety stock, reorder points, and gap analysis. Module 6 covers scenario planning: how to model what-if scenarios without disrupting the baseline plan. Module 7 covers AI agents and human-in-loop. Module 8 covers audit, compliance, and the board pack.
Before moving to Module 6, do this exercise. Pick 10 A-class SKUs from your portfolio. For each, compute the current reorder point and compare it to what the formula suggests given current demand variability and lead time. If your ERP's reorder points differ significantly from the formula's suggestion, you have either a data quality issue (lead time or demand variability is wrong in the system) or a policy issue (reorder points were set manually and not updated). Both are fixable, but only if you know they exist.
Self-assessment
One. What is the supply netting formula, and why must the computation be idempotent?
Two. What are the three assumptions that must be checked before applying the safety stock formula?
Three. How is the reorder point computed, and what happens if it is not updated when safety stock changes?
Four. What is gap analysis, and why does the timing of gap identification matter?
Five. Why does the quality of the demand plan determine the quality of the entire downstream supply chain?
Answers are in Module 6's introduction.