Work from the same stock plan
Picture the next stock review: sales can explain the demand it expects, purchasing can confirm the delivery wait, and both can see why extra stock is needed. Inventory forecasting supports that shared plan by estimating future demand. Keep the estimate separate from delivery timing and the buffer you choose, so a change has a clear reason.
Lead time means the wait from placing an order until the goods are ready to use. Safety stock is the extra quantity held for uncertainty. More safety stock does not make the demand forecast more accurate. It changes how much protection you carry, and how much money remains in stock.
Start with one item at one location. Separate recorded demand from future assumptions, and check days when sales were limited by unavailable stock. Sales on those days may hide what customers wanted. Agree who checks demand, who confirms delivery times and who can change the buffer.
See what a later delivery really changes
Synthetic example, not a client result: a distributor plans demand of ten filters a day, a four-day delivery wait and ten extra filters as safety stock. In this simplified example, it places an order when stock reaches 50: 40 for expected demand during the wait, plus ten extra.
The example starts with 50 usable filters and no earlier orders on the way or unfilled customer orders. If demand stays at ten a day and the delivery arrives after four full days, ten filters remain just before it arrives.
If the delivery takes six days instead, customers need 60 filters before it arrives. Ten cannot be supplied from the starting stock, even though daily demand matched the forecast. Purchasing can now explain the gap: the wait changed, not daily demand. If the team plans for six days, the same rule calls for ordering when stock reaches 70 filters.
Demand can change the result separately. At 14 filters a day over four days, the distributor is six filters short. At six a day, 26 remain. Increasing the chosen buffer from ten to 30 means ordering when stock reaches 70; under the original demand and timing, 30 remain. That is more protection, but also more stock to carry.
Sales and purchasing can use these comparisons to agree what needs to change before promising availability. They do not establish the best stock level. This rule assumes the team can place an order as soon as stock reaches the trigger. Weekly ordering also needs to cover the wait until the next review.
Keep customer commitments grounded in a checked plan
The worked forecast and stock example includes the inputs, a simple forecast check, shortage and surplus cases, and an invalid-input example. All figures are invented. The extra stock is a choice to test. It does not guarantee that a stated share of customer orders will be filled.
Check forecasts against later demand that was not used to build them, as Forecasting: Principles and Practice explains. A short synthetic check cannot establish accuracy for your business. Review real demand patterns, delivery variation, shelf life, storage space and the cost of a shortage before choosing a policy.
Datimore can help bring these records and agreed assumptions into a shared planning view. Our project delivery case shows related reporting and resource visibility, not a tested inventory forecast. Bring one item's demand history and delivery records, and explain how shortages affect its customers. The aim is a stock plan your team can explain, review and adjust before making its next commitment.