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The base stock inventory method replenishes inventory position toward a stated target. Compare supplied targets with stock, open orders, backorders, and the demand assumptions behind the protection period.
The base stock inventory method replenishes inventory position toward an approved target. At each review, subtract the current position from the target and order the positive difference, subject to purchasing constraints. A sound review checks both the arithmetic and whether the target still reflects demand, delivery timing, and service expectations.
Unconstrained replenishment quantity = MAX(0, Base-stock target − Inventory position)
Inventory position = Usable on hand + Open inbound supply − Unfilled demand
This definition assumes no additional reserved commitments outside the unfilled-demand field. If the business subtracts separate commitments, add them explicitly and prevent overlap with backorders. Physical on-hand stock and inventory position answer different questions.
In a continuously reviewed base-stock policy, demand can trigger replenishment unit for unit. A periodic version checks the position at scheduled reviews and orders back toward the target. Purdue's research on periodic base-stock inventory describes the latter as placing an order at fixed intervals to restore inventory position to the base-stock level.
This is different from the inventory reorder level, which is a threshold for deciding when to order. A base-stock target states the position to restore. Keep those fields labeled separately in a workbook.
A target needs a documented protection period: the interval over which demand must be covered before the next relevant replenishment can arrive. For the periodic example below, that interval is replenishment lead time plus the review interval.
Illustrative periodic target = Average daily demand × (Lead time + Review interval) + Approved safety stock
The formula assumes a stable average demand rate, a consistent day basis, and replenishment without an additional delay beyond the supplied lead time. It does not prove a service level. Demand variation, delivery variation, lost sales, or capacity limits require further assessment.
Use the inventory safety stock formula for a separate discussion of the uncertainty buffer. The distinction matters: shortening the review interval reduces expected demand in the protection period, but the right safety allowance still needs review.
Record who approved demand, lead time, and the buffer. Procurement owns supplier assumptions and order constraints; operations confirms usable stock and receiving availability; sales or planning owns the demand outlook. Finance reviews valuation and the cost of carrying stock. One named policy owner should sign off on the resulting target.
Use a stock snapshot, an open-PO export, an open-demand export, and the policy workbook as of the same cutoff. Match SKU, location, and unit of measure across the files before combining them.
The policy workbook should carry the target, effective date, review interval, lead-time basis, and approved safety stock. Keep the current approved target next to any recalculated illustration. Otherwise a workbook can quietly replace a business decision with a formula result nobody approved.
For partial purchase receipts, include only the outstanding quantity in open supply. Exclude canceled lines and isolate overdue supply for a timing review. MIT's practical inventory guidance identifies expected arrival dates, partial orders, and the meaning of on-order stock as recurring inventory-position problems.
An Indiana parts distributor reviews these items every two operating days. All quantities use individual units, all lead times use operating days, and the following buffers are supplied policy inputs.
| SKU | Daily demand | Lead time (days) | Review interval (days) | Safety stock | Protection demand | Base-stock target |
|---|---|---|---|---|---|---|
| Seal | 40 | 3 | 2 | 60 | 40 × (3 + 2) = 200 | 260 |
| Valve | 10 | 4 | 2 | 20 | 10 × (4 + 2) = 60 | 80 |
| Clamp | 30 | 2 | 2 | 30 | 30 × (2 + 2) = 120 | 150 |
The target adds safety stock to protection demand: 200 + 60 = 260 for the seal, 60 + 20 = 80 for the valve, and 120 + 30 = 150 for the clamp. These are supplied assumptions applied transparently, not targets claimed to minimize cost.
At the review cutoff, the stock and commitment files show:
| SKU | Usable on hand | Open inbound | Unfilled demand | Inventory position | Target | Unconstrained order |
|---|---|---|---|---|---|---|
| Seal | 120 | 80 | 20 | 180 | 260 | 80 |
| Valve | 65 | 15 | 0 | 80 | 80 | 0 |
| Clamp | 160 | 0 | 0 | 160 | 150 | 0 |
| Total units | 345 | 95 | 20 | 420 | 490 | 80 |
The seal position is 120 + 80 − 20 = 180 units, so the indicated quantity is 260 − 180 = 80 units. The valve already meets its target. The clamp exceeds its target by 10 units, so its indicated purchase is zero.
Do not net the clamp surplus against the seal shortage. Total target less total position is 490 − 420 = 70 units, but that would understate the required seal replenishment. Different SKUs are not substitutes merely because the table shares a total row.
After adding each indicated order to its position, the seal reaches 260 units and the valve remains at 80. The clamp remains at 160, above its 150-unit target. Total position becomes 420 + 80 = 500 units; the 10-unit difference from total targets is the existing clamp excess.
For an acquisition-cost comparison, the supplier workbook gives:
| SKU | Indicated units | Unit cost (USD) | Indicated purchase value (USD) |
|---|---|---|---|
| Seal | 80 | 12 | 960 |
| Valve | 0 | 45 | 0 |
| Clamp | 0 | 4 | 0 |
| Total | 80 | 960 |
The indicated purchase is $960 before freight, tax, or other terms. It is a purchasing comparison, not immediate cost of goods sold: unsold inventory and expense recognition must follow the company's accounting policy.
Change only the seal's lead time from three to four operating days. Its target becomes 40 × (4 + 2) + 60 = 300 units; the indicated quantity becomes 300 − 180 = 120 units, costing $1,440. The longer assumed delay adds 40 units and $480 of proposed purchasing value. That sensitivity gives the buyer a concrete question to resolve with the supplier.
Bring your approved target workbook, stock snapshot, open orders, and demand export. Covirage maps the columns, and its tools compute and check inventory position and target gaps; the external AI model explains the comparisons with every figure traced to its rows. Create a free Covirage account and bring a sample of your own data.
See Covirage for supply chain teams for related operational reviews.
No. Base stock is the total target used in the replenishment policy. Safety stock is the buffer within that target for uncertainty. A target can include expected demand over the protection period as well as an approved safety allowance.
The target usually applies to inventory position, which includes open replenishment and subtracts unfilled demand. Physical stock can therefore be below the target while the position is already at it. Check the policy definition before comparing a warehouse count with a planning target.
The basic calculation produces no new order. It does not create a negative purchase or automatically cancel an existing commitment. The buyer reviews excess, timing, contractual obligations, and possible transfers separately before taking action.
Shared assumptions are only useful when demand patterns, replenishment timing, service needs, and constraints are sufficiently similar. Keep the target by SKU and location, with its effective date and owner. A common formula does not make different business risks equivalent.