Check what the next receipt must cover
Replenishment connects a demand estimate with the time needed to obtain usable stock. Lead time includes more than transport: ordering cutoffs, supplier processing, receiving and any inspection can all matter. An order arriving at the loading area is not necessarily available for sale that minute. Measure the interval relevant to the operational decision.
Distinguish shelf replenishment from purchasing. Moving units from a stockroom to a display improves shelf availability without increasing total store inventory. Buying more units when stock is merely in the wrong place can worsen congestion while leaving the original handling problem unresolved.
Define inventory position consistently
A common starting point is usable on-hand stock plus valid on-order supply, minus backorders or other commitments not already deducted. Your calculation must state how reservations and allocations are treated. Subtracting the same commitment twice understates stock; ignoring it overstates the units available to meet new demand.
Not every open purchase order deserves equal confidence. An overdue order without a confirmed delivery date may need separate treatment from a confirmed shipment. Keep both the quantity and expected availability date. A single total of incoming units can hide a shortage this week and a surplus next month.
Separate the trigger from the quantity
In a continuous-review policy, a reorder point can be expressed as expected demand during lead time plus safety stock. Crossing that point triggers an ordering decision. It does not, by itself, specify the quantity to order. That quantity may follow a fixed-lot policy, an order-up-to target or a constrained planning process.
Worked example Suppose expected demand is 6 units per day and usable supply takes 5 days to arrive. Expected lead-time demand is 30 units. With an illustrative buffer of 10 units, the reorder point is 40. If usable on-hand stock is 32, confirmed incoming supply is 12 and commitments not yet deducted are 8, inventory position is 36.
| Calculation | Result |
|---|---|
| Expected lead-time demand: 6 × 5 | 30 units |
| Reorder point: 30 + 10 | 40 units |
| Inventory position: 32 + 12 − 8 | 36 units |
| Compare position with trigger | 36 is below 40; review an order |
Assume separately that the chosen policy orders up to 70 units. The unconstrained quantity would then be 70 − 36 = 34 units. If the supplier sells only cases of 12, rounding up produces 36 units and a post-order position of 72. This is a deliberate trade-off, not evidence that 72 is an optimal stock level.
Allow for review timing and uncertainty
If orders are reviewed only once a week, demand during the review interval also matters. A periodic-review order-up-to policy typically protects the review interval plus lead time. Applying only a lead-time calculation can leave the store exposed before the next ordering opportunity.
Safety stock addresses uncertainty, not routine demand that was omitted from the forecast. One simplified expression is a service factor multiplied by the standard deviation of lead-time demand. That expression needs assumptions about distributions, stability and the meaning of service. Cycle service level and fill rate are different measures; a target for one cannot be treated automatically as the other.
Apply the real constraints before release
Check minimum order quantities, case sizes, delivery calendars, cash limits, shelf capacity and storage conditions. For perishable goods, an apparently economical large order can create avoidable waste. First-expired, first-out, or FEFO, prioritises expiry dates; first-in, first-out, or FIFO, prioritises receipt sequence. They coincide in some situations, but not all.
The economic order quantity, or EOQ, model offers a useful explanation of ordering and holding cost trade-offs under restrictive assumptions. It should not override shelf life, erratic supply or a binding storage limit. Record which constraint changed a proposed order so the next review can distinguish a forecasting problem from a supply or capacity decision.
Before allowing automatic release, run proposed orders alongside the existing process. Examine misses, overstocks and overrides. Set approval limits and an exception route for unusual quantities, stale inputs or uncertain deliveries. Automation should make normal decisions repeatable while leaving abnormal ones visible.
Method labels used here: reorder point, order-up-to policy, safety stock, EOQ, FIFO and FEFO. No numerical example is a service-level recommendation or a supplier commitment.