Use one consistent time unit
A basic model is average daily unit demand multiplied by replenishment lead time in days, plus a safety-stock buffer. InFlow's reorder guide presents this model. Keep all inputs on the same basis: calendar-day demand should use calendar-day lead time; working-day demand needs a matching working-day measure.
Decide where the clock starts and ends. “Supplier transit time” may omit order approval, processing or receiving inspection. For an operating model, document the interval your team must actually cover. Use records that reflect the relevant product and supply path. A supplier's advertised lead time and your observed replenishment time are different inputs, and should be labelled accordingly.
Calculate a transparent example
In a fictional workshop, a consumable moves at an average of four units per working day. Its documented planning lead time is six working days, and the team chooses eight units as a buffer. Expected lead-time demand is 4 × 6 = 24 units. The illustrative reorder point is 24 + 8 = 32 units.
That arithmetic does not justify the eight-unit buffer; the team must explain it separately. Nor does reaching 32 mean ordering 32 more. Purchase quantity depends on the desired coverage, existing incoming orders, pack sizes, storage space and other constraints. Keep the trigger calculation and the buying decision in separate fields so nobody mistakes one for the other.
Review the stock position and the dates
Before placing a new order, inspect existing commitments and open purchase orders. A confirmed delivery arriving tomorrow may change the decision. A long-overdue order with no new date should not be treated as dependable coverage solely because it remains open.
If the product was unavailable for part of the observation period, recorded sales may understate what customers wanted. If one unusual order dominates the history, a simple average may not describe routine demand. Flag these limitations rather than presenting the calculated point as optimal. New products without useful history need a labelled provisional assumption and an early review, not a fabricated data-driven answer.
Test the trigger against real decisions
Choose a small set of ordinary stocked items and record the inputs, date and owner of each calculation. Review what happened at the next replenishment: was the trigger noticed, was the order actually placed, and did the planned lead time resemble the observed one?
A spreadsheet can make the model transparent; inventory software helps surface quantities and alerts across many products. Neither substitutes for someone acting on the alert or correcting poor inputs. Revisit the model after material demand or supplier changes, without claiming that any fixed review interval fits every business. Your next action is to calculate one product's trigger with an explicit time basis, then inspect open supply before deciding whether a purchase is actually needed.
Sources used for this page
These records support the facts and comparisons above. Merchant-controlled records are labelled so you can separate product claims from independent evidence.
- inFlow: reorder-point model — Merchant documentation · inflowinventory.com · Merchant-controlled · checked 2026-09-24