Inventory carrying cost: calculate the rate behind your EOQ
Calculate your annual inventory carrying-cost rate with a worked example. Separate fixed costs, cash savings and the holding cost to enter in EOQ.
Inventory carrying cost is the yearly cost of keeping stock: the cost of capital tied up in it, storage, inventory-related services and losses. Calculate it against average inventory at cost for the same period. That gives you an annual percentage you can use to compare order quantities and supplier minimums.
Before you accept a supplier's price break, calculate what it costs to hold the extra stock. The same rate goes into EOQ. Build it from your own records so you can compare a large discounted order with smaller, more frequent deliveries.
What is the inventory carrying cost formula?
Annual carrying cost = average inventory value × annual carrying-cost rate.
For example, $600,000 of average purchased-parts inventory at a 20% annual rate has a carrying cost of $120,000 a year. The inventory remains an asset; $120,000 is the estimated yearly cost of holding it. The 20% is an illustrative assumption, not a manufacturing benchmark.
To build the rate, work in the other direction:
Annual carrying-cost rate = annual holding costs ÷ average inventory value × 100%.
Use inventory valued at cost, not sales revenue. Use the same stock and period on both sides of the calculation. For purchased components at one site, use that site's average component inventory. Do not divide a full year's warehouse costs by one unusually low year-end balance. Monthly balances are a practical starting point; daily balances are better when receipts are uneven.
Which costs belong in the rate?
Group the costs into four buckets and count each cost once. The ASCM chapter's carrying-cost breakdown separates capital, services, space and inventory risk.
| Cost bucket | Evidence to collect | Check before including it |
|---|---|---|
| Capital | A finance-approved annual cost-of-capital rate applied to average inventory | Do not add loan interest again if the chosen rate already includes financing |
| Storage | Space, utilities or external storage attributable to this inventory | Separate allocated rent from space charges that change with the stock held |
| Services | Inventory insurance, applicable inventory taxes and holding-related handling | Keep per-order receiving and administration in order cost; avoid counting them again here |
| Risk | Expected annual obsolescence, damage and shrinkage losses, net of recoveries | Reconcile provisions and write-offs so the same loss appears once |
Use recent losses to inform next year's risk allowance, adjusting for product changes, shelf life and unusual events. A reserve balance is not an annual expense. Neither is every stock adjustment a new loss: disposal of inventory already written down must not be charged twice.
How do you calculate a rate from your own records?
Here is an illustrative worksheet for one site's purchased components. Average inventory at cost is $600,000, calculated from twelve monthly balances. All costs cover the same twelve months and the same stock.
| Component | Annual amount | Share of average inventory |
|---|---|---|
| Capital at an assumed 10% | $60,000 | 10% |
| Storage allocated to the components | $30,000 | 5% |
| Insurance and holding-related services | $12,000 | 2% |
| Expected losses after recoveries | $18,000 | 3% |
| Total | $120,000 | 20% |
The check is $120,000 ÷ $600,000 = 20%. Keep the underlying ledger accounts, allocation basis and owner beside each row. For a spreadsheet, put average inventory in B2 and the four annual amounts in B3:B6. Enter =SUM(B3:B6)/B2 in B7 and format B7 as a percentage. Do not multiply by 100 again when using percentage formatting.
The 20% includes every cost allocated to these components. Order less stock and the warehouse rent may stay the same. Ask finance which costs would fall over the period you are comparing.
What rate should you enter in the EOQ calculator?
For an order-size decision, use the annual costs that change when average stock changes. Fixed warehouse rent may belong in a full-cost report while contributing nothing to a short-term lot-size decision. Capacity freed for another use can still have economic value; document that use instead of calling it a rent saving.
Suppose the worksheet's entire 5% storage allocation stays fixed, while the other costs vary proportionately over the planning horizon. The relevant rate for that decision is 15%, not 20%. Check with finance whether the remaining costs would change in proportion to stock.
The EOQ model needs an annual holding cost per unit, H. Oracle's EOQ documentation calculates it from unit cost and the annual carrying percentage:
H = unit cost × annual carrying-cost rate.
A $40 component at 15% gives H = $6 per unit per year. Enter 15 in the annual percentage field of our EOQ calculator, together with annual demand and cost per order. With steady demand of 2,400 units a year and $60 per order, EOQ = √(2 × 2,400 × 60 ÷ 6), or about 219 units, before MOQ and pack-size constraints.
That basic model assumes steady demand and replenishment in complete lots. Use the MOQ vs EOQ guide when the supplier's minimum or price break changes the feasible order. Use MRP for time-phased component demand rather than forcing it into a steady average.
How much cash does a stock reduction actually save?
A sustained $100,000 reduction in average inventory gives a headline estimate of $20,000 a year if you multiply by the original 20% rate. That shortcut wrongly scales down fixed storage too. Under our assumptions, the recalculated annual cost is $105,000: $50,000 capital, $30,000 unchanged storage, $10,000 services and $15,000 expected losses. The economic cost falls by $15,000, not $20,000.
Of that $15,000, $10,000 is the value of putting the released capital to work elsewhere, $2,000 is variable services and $3,000 is lower expected losses. Storage costs remain unchanged. Actual interest savings depend on whether you repay debt. Service bills must actually fall, and avoided losses are uncertain. Report the components separately rather than promising $15,000 of lower bills or profit improvement.
Cash released from inventory is a separate, one-time effect. It depends on how you reduce stock, payment timing and any disposal discount. The working-capital guide covers those decisions. Keep confirmed supplier dates and production need dates beside the reduction list so a carrying-cost target does not create a shortage.
When should you update the rate?
Revisit it when financing rates, storage contracts, insurance, product mix or loss experience change. Separate expensive-to-store or short-life parts when a site average hides a large difference. Run a low and high rate through the same order-size comparison when an estimate is uncertain.
Keep the calculation with its stock list, cost accounts and approval date. Record how you valued the stock, which balances you averaged, and which costs you expect to change. A buyer can then explain why an EOQ changed without rebuilding the calculation from memory.
Questions teams ask
Are carrying cost and holding cost the same?
They usually name the same planning cost. Check whether a quoted figure is an annual percentage of inventory value, a cost per unit per year, or an annual total. Those units are not interchangeable.
Is 20% a good carrying-cost rate?
It is only the illustrative result in this article. Calculate your own rate from the stock, costs and decision horizon you are evaluating. The rate for short-life material can differ substantially from that for standard metal parts.
Does carrying cost include the purchase price?
The purchase price supplies the inventory-value base; it is not added as another annual holding expense. A $40 unit at a 15% annual rate incurs $6 of annual holding cost. It does not incur $46 of holding cost.
Should you use an annual rate for a three-month comparison?
For a simple estimate with a constant balance, multiply inventory value by the annual rate and by 3/12. If stock runs down or arrives in batches, use its time-weighted average over those months. Check fixed charges and loss risks separately rather than assuming every cost scales evenly with time.