Inventory carrying cost formula
Inventory carrying cost is what it costs you to hold unsold stock for a period of time. This guide gives you the formula, the four groups of cost to include, a worked example with made-up numbers, and practical ways to bring the cost down, including just-in-time ordering.
What inventory carrying cost is
Inventory carrying cost, also called holding cost, is the total expense of storing and owning inventory that has not sold yet. It includes obvious items such as storage and insurance, and less visible ones such as the return you give up on cash tied up in stock and the value lost when products are damaged, expire or go out of style.
It is usually expressed as a percentage of inventory value per year. That percentage feeds directly into purchasing decisions: how much to order at once, whether a volume discount is worth taking, and how much safety stock to keep.
The carrying cost formula
The rate is your total annual carrying costs divided by your average inventory value:
To turn a rate into a dollar amount for a given amount of stock:
Keep the units consistent:
- Total annual carrying costs is the sum of the four cost groups below, in dollars over twelve months.
- Average inventory value is stock valued at what you paid for it, not at selling price. Use (beginning inventory + ending inventory) ÷ 2, or the average of several month-end values if your stock level swings during the year.
- If you measure a shorter period, such as a quarter, scale the costs to a full year or label the result as a quarterly rate. Never compare a quarterly rate with an annual one.
The four components of carrying cost
Leaving out a group is the easiest way to end up with a number that is too low.
1. Capital cost
This is the cost of the money tied up in inventory. If you borrowed to buy stock, it is the interest you pay. If you used your own cash, it is the return you could have earned by using that cash elsewhere, for example on marketing or paying down debt. Because it applies to every dollar of stock, it grows and shrinks with your average inventory value.
Example: say you hold $80,000 of inventory on average and your cost of capital is 10% a year. Capital cost = $80,000 × 10% = $8,000 per year.
2. Storage cost
Everything tied to the physical space your stock occupies: rent for the storage area, utilities, shelving, handling equipment, labor for receiving and putting away stock, and fees from any third-party warehouse.
Example: say a third-party warehouse charges $15 per pallet position per month and you average 40 pallets. Storage cost = 40 × $15 × 12 = $7,200 per year.
3. Service cost
The cost of protecting and administering the stock: insurance, any inventory or property taxes that apply where you operate, inventory-tracking software and security.
4. Risk cost
The value you lose on stock that does not sell at full price, or does not sell at all:
- Obsolescence: products that go out of season or are replaced
- Shrinkage: theft, errors and miscounts (see inventory shrinkage)
- Damage: products broken in storage or handling
- Markdowns: discounts taken to clear slow stock (see dead stock management)
- Expiry: perishable goods that pass their date before they sell
Example: say last year you wrote off $4,500 of damaged goods and $2,000 of expired products, and cleared stock that normally sells for $6,000 at 50% off, giving up $3,000 of revenue. Risk cost = $4,500 + $2,000 + $3,000 = $9,500.
Worked example
Using the hypothetical figures above, plus an assumed $2,400 for insurance, software and taxes, for a store with $80,000 of average inventory at cost:
| Cost component | Annual cost | Share of average inventory value |
|---|---|---|
| Capital cost | $8,000 | 10.0% |
| Storage cost | $7,200 | 9.0% |
| Service cost | $2,400 | 3.0% |
| Risk cost | $9,500 | 11.9% |
| Total | $27,100 | 33.9% |
Carrying cost rate = $27,100 ÷ $80,000 = 0.33875, or about 33.9% per year. Each $1,000 of stock costs roughly $339 a year to hold.
These figures are illustrative. Your own rate depends on your financing, storage arrangement, product type and loss history, so there is no single right number. The most useful comparison is your own rate from one quarter to the next.
Carrying cost per unit and the EOQ formula
Purchasing formulas need the holding cost of a single unit for a year:
This is the input to the economic order quantity, the order size that minimizes ordering plus holding cost:
D is annual demand in units, S is the cost of placing one order in dollars, and H is the holding cost per unit per year. A higher carrying cost rate means a smaller optimal order.
When a volume discount is a trap
A supplier offers a lower price if you buy more. The discount is only worth taking if it exceeds the cost of holding the extra units until they sell:
Total discount savings is the price cut per unit times every unit in the larger order. Extra months is how much earlier the extra units arrive than they would in a separate, later order. Use the carrying cost rate as a decimal here too.
Say a unit costs $20 when you buy 500, and $19 (5% off) when you buy 1,000. Your carrying cost rate is 25%, and the extra 500 units would sit for 8 additional months.
- Discount savings = 1,000 units × $1 = $1,000
- Extra holding cost = 500 × $19 × 25% × 8 ÷ 12 = $1,583
- Net benefit = $1,000 − $1,583 = −$583, so the discount loses money
At 20% off ($16 per unit) the savings are $4,000 against holding cost of 500 × $16 × 25% × 8 ÷ 12 = $1,333, a net gain of about $2,667. With these inputs the break-even discount is about 7.7%. If the larger order also saves the admin and freight of a second order, add that to the savings.
Ways to reduce carrying cost
- Order closer to what you will sell. Buying the right amount avoids overstock without causing stockouts. See demand forecasting.
- Raise inventory turnover. For the same sales, faster turnover means less average inventory. See inventory turnover ratio.
- Spend attention where the money is. ABC analysis shows which items hold most of your inventory investment, so you can run leaner on low-value items.
- Shorten lead times and reduce minimums. Shorter, more consistent lead times let you hold less safety stock. Ask suppliers about faster processing, smaller minimum orders or consignment.
- Right-size reorder points and safety stock. Calculate buffers from demand variability and lead time instead of gut feel. See the reorder point formula and safety stock formula.
- Clear dead stock and cut shrinkage. Pick a threshold for "dead" that fits your products, for example no sales in 180 days, and review it regularly. Options include markdowns, bundles, liquidation and donation (check the tax treatment with an accountant). For losses from theft, errors and miscounts, see inventory shrinkage.
Just-in-time ordering
Just-in-time (JIT) means ordering and receiving stock close to when you need it instead of buying far ahead. The aim is to hold the least inventory that still meets demand, which lowers the capital, storage and risk costs above and the insurance and tax part of service cost.
In e-commerce, JIT rarely means zero inventory. It means right-sized inventory: enough cover for supplier lead time and demand variability, bought in smaller and more frequent batches. The reorder point still applies:
Demand is in units per day and lead time in days, so the first term is in units, like safety stock. See the reorder point formula for how to set each term.
The trade-off, with numbers
Smaller orders cut average stock but raise the number of orders, and sometimes the unit price. More frequent ordering pays when the extra annual cost (extra orders × cost per order, plus any unit price premium) is lower than the carrying cost saved.
Say you sell 4,000 units a year, a unit costs $20, your carrying cost rate is 25% (so H = $5 per unit per year), and each order costs $40 in admin and freight. Assume steady demand, so average cycle stock is half the order quantity, and ignore safety stock, which you hold either way.
| 4 orders of 1,000 | 16 orders of 250 | |
|---|---|---|
| Average cycle stock | 500 units | 125 units |
| Holding cost | 500 × $5 = $2,500 | 125 × $5 = $625 |
| Ordering cost | 4 × $40 = $160 | 16 × $40 = $640 |
| Total | $2,660 | $1,265 |
Smaller, more frequent orders save $1,395 a year. If the supplier charges $0.10 more per unit for small orders, that costs 4,000 × $0.10 = $400, and you still come out $995 ahead. For these inputs the EOQ is √(2 × 4,000 × $40 ÷ $5) = √64,000, about 253 units, so an order size of 250 is close to the cost-minimizing point.
When JIT fits, and when it does not
It fits when supplier lead times are short and reliable, demand is fairly steady, holding cost per unit is high (perishable, bulky or expensive items) and suppliers accept small orders. It fits poorly when:
- lead times are long or vary widely, so the safety stock you need cancels out the savings
- products are strongly seasonal and you build stock ahead of the peak (see seasonal inventory planning)
- suppliers set large minimum orders
- the product is new and has no sales history to forecast from
Common JIT mistakes
- Going lean everywhere at once. Start with a few fast-moving SKUs that have dependable suppliers, then expand.
- Planning on best-case lead time. If a supplier delivers in 5 to 15 days, base the buffer on the slower end.
- Forgetting planned promotions. Raise reorder points ahead of a known sale.
- Trusting inaccurate counts. If the system says 50 units and you hold 30, a lean plan will stock out. See preventing stockouts.
Tracking carrying cost over time
- Calculate average inventory value each month.
- Record each of the four cost groups separately, so you can see which one moves.
- Calculate the rate each quarter, with costs scaled to a full year, and watch the trend.
- Look at carrying cost by SKU. Items that are expensive to hold and earn a low margin are the first candidates for smaller orders or removal.