Inventory carrying cost: the formula, and the cash safety stock ties up
Inventory carrying cost is the annual cost of holding stock, written as a percentage of the average value of that stock: annual holding cost divided by average inventory value, times 100. This page gives you the formula, what belongs in the top half of it, and how to use it to price the safety stock you are carrying on your hero SKUs.
The formula
Carrying cost rate = (annual holding cost / average inventory value) x 100
And in money, once you have a rate:
Carrying cost = average inventory value x carrying cost rate
Two inputs, both of which you already own. Average inventory value is the landed cost of the stock you hold on an average day, not its retail price. Annual holding cost is everything you pay over a year because that stock exists rather than the cash.
Most merchants get the bottom half right and the top half wrong. They count warehouse rent and stop. The number only becomes useful when you include the cost of the money and the cost of the stock going bad.
What goes into annual holding cost
| Cost bucket | What sits in it | Where you find the number |
|---|---|---|
| Cost of capital | The money paid for stock is money you cannot spend on ads, a new line, or payroll. If you borrowed it, it is interest. | Your loan or credit line rate, or your own judgement of what the cash would have earned. |
| Storage | The share of rent, shelving, racking and utilities your stock takes up, or the per-unit fee a 3PL charges. | Your lease or 3PL invoice, apportioned by the space inventory actually occupies. |
| Handling | Time spent receiving, counting, moving and picking. For a small store this is usually your own hours. | Hours per week on stock work, costed at what that hour is worth. |
| Insurance and tax | Premiums tied to stock value, plus any local inventory or property tax on goods held. | Your policy schedule and tax statements. |
| Risk and shrinkage | Damage, theft, expiry, and the big one for apparel and seasonal goods: markdowns on stock that aged out. | Last year's write-offs and markdown total, divided across the year. |
A worked example
These figures are illustrative, not a benchmark. Use your own.
Say one SKU, a candle, lands at $6 a unit. Across the year you hold an average of 400 units, so your average inventory value for that SKU is $2,400.
Now the top half. Capital: you funded stock on a credit line, and your share of interest attributable to this SKU over the year is $200. Storage and handling: $250. Insurance and tax: $50. Risk: $100 written off in damage and discontinued scents. Annual holding cost is $600.
$600 divided by $2,400 is 0.25. The carrying cost rate is 25 percent.
Read that back: every dollar of candle stock costs you 25 cents a year to hold. That is the number you weigh against the cost of running out. One of those costs is visible on your bank statement; the other shows up as a sale that never happened.
The cash safety stock ties up
Safety stock is the buffer you hold above lead time demand so a supplier delay does not empty the shelf. It is insurance, and like insurance it has a premium. Your carrying cost rate is the premium.
Cost of safety stock = safety stock units x unit cost x carrying cost rate
Staying with the candle at a 25 percent rate: 120 units of safety stock at $6 is $720 of stock held permanently in reserve, and holding it costs about $180 a year.
If you size your buffer as a percentage on top of lead time demand rather than a flat number of units, the same arithmetic holds. Work out the units that percentage produces for a SKU, cost them at landed cost, apply your rate, and you have the annual premium for that one line.
That is the trade-off in one line. More safety stock means fewer stockouts and more cash parked on a shelf. Less safety stock frees the cash and moves the risk onto your supplier's punctuality. Carrying cost does not make the decision for you, but it stops the decision being a guess, because it puts both sides in the same unit: dollars per year.
Two things make the premium worse than the arithmetic suggests. Long lead times force a bigger buffer, so the slowest suppliers quietly carry the highest holding cost. And buffer stock that never turns is the raw material of dead stock, where the risk bucket stops being a percentage and becomes a markdown.
Related terms
Carrying cost sits in the middle of a small cluster of numbers. Each one is worked through on its own page in this pillar.
- Safety stock: the buffer carrying cost prices. Size it first, then cost it.
- Days of inventory on hand: how long your current stock lasts at current velocity. Long cover and a high carrying rate is expensive cover.
- Inventory turnover: how many times a year stock cycles. Turnover and carrying cost move in opposite directions.
- Economic order quantity: the formula that balances carrying cost against ordering cost to pick an order size. It needs your carrying rate as an input.
- Dead stock: where carrying cost ends up if the risk bucket is ignored.
- Reorder point: the trigger level. Carrying cost tells you what the buffer inside it costs.
Questions
What is the inventory carrying cost formula?
Annual holding cost divided by average inventory value, times 100, gives you a carrying cost rate as a percentage. Multiply average inventory value by that rate to get the cost in money. Average inventory value is at landed cost, not retail.
What is a normal carrying cost percentage?
Figures get quoted widely and we are not going to repeat one we cannot source for you. Build your own instead: it takes an afternoon with your lease, your credit line rate, your insurance schedule and last year's write-offs, and it is the only version that reflects your actual store.
Is carrying cost the same as holding cost?
In practice the terms are used interchangeably. Holding cost usually names the dollar total for the year, and carrying cost rate names that total as a percentage of average inventory value.
Should I calculate carrying cost per SKU or for the whole store?
Do the store level first, because most of the inputs such as rent, insurance and your cost of capital are store-wide. Then apply the resulting rate per SKU when you want to price a specific decision, like how much safety stock a slow supplier justifies.
Does carrying cost include the purchase price of the stock?
No. The purchase price is the cost of the goods. Carrying cost is what you pay on top because the goods sit with you rather than with a customer, including the cost of having that purchase money tied up.
How does carrying cost change how much I reorder?
A high rate pushes you towards smaller, more frequent orders and a leaner buffer. A low rate, or a supplier with steep per-order costs or minimums, pushes the other way. Economic order quantity is the formula that balances the two.
Can Restoc tell me my carrying cost?
No. It is built to give you the units, not the money. Restoc takes a sales velocity window of 7, 14 or 30 days, the lead time you enter per SKU and a store-wide safety stock percentage, works out a reorder point, and shows safety stock units and days of inventory remaining per SKU. Per tracked SKU it stores the title, your own SKU code, the Shopify variant id, current stock, lead time and the computed reorder point, and separately sales quantities and dates with the Shopify order reference. There is no field anywhere for a landed cost, a rent figure or an insurance premium.