Test a Reorder Trigger Against Explicit Planning Assumptions

A proposed reorder trigger is useful only when the owner can explain what would make it change. Test the rule against explicit assumptions before adopting it. A neat calculation can show how a decision reacts to a longer replenishment interval; it cannot establish the supplier’s actual timing or guarantee that stock will cover every requirement.

This article develops an original, simplified sensitivity worksheet for a continuous-review proposal. “Continuous” here means evaluating the trigger whenever a relevant position change is reviewed, rather than waiting for a fixed scheduled review date. It does not claim that the reader has an automated system or real-time information. No actual consumption history, supplier commitment or approved replenishment policy has been supplied.

Define the proposed decision rule

State the item, unit, eligible position definition and comparison rule. For the hypothetical worksheet below, the trigger is “request owner review when the position is at or below the threshold.” That is an equality-inclusive rule: a position of 28 against a threshold of 28 triggers review. Another chosen convention would need to be written explicitly.

The rule opens a decision; it does not select a purchase quantity or authorize a supplier order. Keep the review request, proposed quantity, commercial checks and final authorization as separate states. A position below a threshold can justify checking inputs without proving that a particular order is the right response.

Name who owns each input and who may approve the rule. If a number is missing, do not borrow an industry average merely to fill the worksheet. Use a labelled teaching assumption for the exercise or leave the actual policy decision unresolved.

Define the simple model and its limits

For this illustration, the threshold equals assumed consumption per day multiplied by the assumed interval from replenishment decision to eligible availability, plus an owner-chosen buffer in units. All quantities concern one established passive-part identity and one consistent unit.

The interval is an elapsed planning assumption, not just the time a supplier spends making an item. Define its start and end milestones. If several stages sit between a decision and eligible availability, state which the assumption covers rather than adding undocumented stage durations. No transport route or delivery promise is implied here.

The consumption rate is deliberately constant in the example. It does not represent lumpy dated commitments or measured demand variability. The buffer is an explicit extra quantity chosen for the scenario; no probability, optimality or service level is attached to it. Selecting a real buffer requires a separate owner judgment and supporting evidence.

Do not add a periodic-review interval to this model. A scheduled-review policy asks a different coverage question. If the owner only checks every seven days, calling the calculation continuous does not remove the time between checks; the periodic approach needs its own clearly defined horizon.

Match the threshold to the position

Compare like with like. The worksheet position must preserve eligible on-hand, supported unreceived inbound and outstanding obligations according to one declared netting convention. Show the inbound availability dates separately. A positive aggregate position can conceal a requirement that occurs before the supply becomes eligible.

For the examples here, assume no outstanding firm obligations or reservations have already been deducted from the comparison position. The assumed future consumption therefore appears only in the threshold. If the real position already subtracts demand also represented in the threshold, reconcile that overlap before comparing them; do not charge the same future need twice.

Likewise, keep the buffer in one place. If stock has been removed from the position solely to protect the same buffer added to the threshold, the comparison has imposed that protection twice. A separately protected allocation may be legitimate, but its purpose and demand membership must be distinct and documented.

Build a one-change-at-a-time worksheet

Every entry is hypothetical. The comparison position of 32 is held constant to isolate each threshold change. The table does not suggest that a real inventory position would remain unchanged while time passes or consumption occurs.

The baseline arithmetic is 2 times 10 plus 8, giving 28 units. At a position of 32, the proposed rule does not open a review. Increasing only the assumed interval to 15 days gives 2 times 15 plus 8, or 38. The same position now meets the review condition.

Changing only consumption from two to three units a day also gives 38, using the original ten-day interval. The identical result comes from a different assumption. Record the cause so the owner knows whether the outstanding question concerns demand or timing.

Test the decision boundary rather than chasing a perfect number

With the baseline consumption and buffer held fixed, an assumed 12-day interval gives a threshold of 32 units: 2 times 12 plus 8. Because the example rule includes equality, the unchanged 32-unit position triggers review at that boundary.

That is a useful owner question: is the evidence sufficient to choose an interval assumption on one side of this decision boundary? It is not a claim that 12 days is a supplier lead time. If the answer depends on an unverified milestone, direct the next check to that input rather than refining irrelevant decimal places.

A combined stress case can follow the individual tests. Three units a day over 15 days plus eight buffer units gives 53. Label that as two assumptions changed together. Do not present it as the expected case merely because it produces the largest threshold, and do not assign an unsupported likelihood.

Keep all scenario rows, including those that do not change the review decision. They reveal which uncertainties matter to this particular threshold test. Avoid deleting inconvenient results to make a proposed rule look robust.

Separate uncertainty from an operational commitment

The finished worksheet should identify its candidate rule, assumptions, input owners, sensitivity results and unresolved evidence. Have the owner decide whether to adopt, revise or defer the proposal. Record that decision and the circumstances requiring another review.

A longer scenario interval may motivate a supplier timing question, but it does not amend an existing order or establish a right to expedite or cancel. A trigger crossing also says nothing about minimum order quantities, product substitution or safe storage. Those issues remain outside this calculation.

Before applying the rule to actual stock, obtain the relevant current records and verify that the demand and position definitions remain compatible. The output is a transparent threshold sensitivity, not a forecast, purchase instruction or guarantee against shortages.

Frequently asked questions

Does consumption times replenishment time guarantee the right reorder point?

No. Here it is a deliberately simplified scenario calculation using constant assumed consumption and an explicit extra buffer. It contains no measured variability, service-level target or supplier guarantee. The owner must assess real evidence, dates and the limits of the proposed rule before using it.

Why change one assumption at a time?

It identifies which input changes the review decision. In the example, either a longer interval or a higher consumption assumption moves the threshold from 28 to 38, but those results call for different evidence checks. Combined stress cases can follow if their simultaneous changes remain clear.

Should a seven-day review interval be added to this threshold?

Not within this stated continuous-review model. If actual decisions occur only on scheduled review dates, use a periodic-review calculation whose horizon explicitly includes the interval until the next review and subsequent replenishment. Do not mix the two policies while keeping the same label.

Does crossing the trigger authorize a reorder quantity?

No. This example triggers owner review only. The quantity, timing, existing inbound, demand overlap and commercial authorization still require their own decisions. Preserve the distinction between a calculated threshold, a review request and an approved supplier commitment.