Cycle stock is the inventory that rises and falls because you replenish in batches. Under the basic instantaneous-replenishment model, average cycle stock is approximately Q ÷ 2, where Q is the replenishment quantity. It is separate from safety stock.
Cycle Stock Calculator
Translate an order quantity into average working inventory
Cycle stock formula
When a replenishment of Q units arrives at once and the batch is consumed steadily down toward zero before the next replenishment, the cycle-stock component ranges from approximately Q to 0. Its time-weighted average is therefore Q ÷ 2. If safety stock is also held, total on-hand inventory immediately after receipt can exceed Q; that is why the calculator labels Q as the batch-cycle peak rather than total maximum inventory.
For example, an order quantity of 500 units gives average cycle stock of about 250 units. If annual demand is 10,000 units, that order quantity implies about 20 replenishment cycles per year under the simplified model.
Cycle stock vs safety stock
Cycle stock exists because replenishment occurs in batches. Safety stock is additional buffer inventory held for uncertainty in demand and/or replenishment. Changing safety stock does not change Q/2 unless your replenishment policy also changes the order quantity.
How cycle stock connects to EOQ
If Q is chosen using the classic EOQ model, average cycle stock at the EOQ is EOQ ÷ 2. EOQ chooses an economic batch size by balancing ordering and cycle-stock holding costs; this calculator simply translates a chosen batch size into its average cycle-stock implication.
Where Q/2 is not enough
The Q/2 relationship is a simplified model. Gradual production replenishment, overlapping orders, variable lot sizes, quantity discounts, capacity constraints, planned shortages, perishability and other operating conditions can require a different inventory model. Also distinguish average on-hand inventory from inventory position or pipeline inventory.
Related tools
Use the EOQ Calculator if you need to estimate an economic replenishment quantity. Use the Safety Stock & Reorder Point Calculator for uncertainty buffers and replenishment timing, and the Inventory Turnover Calculator to evaluate inventory efficiency.
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