Inventory management is the practice of keeping enough stock to meet demand without tying up more cash than you need. The basics are simple: measure how fast each category sells, reorder based on real sales and supplier lead times, and clear out slow stock before it becomes dead stock. Every dollar sitting on a shelf is a dollar that can't pay bills, fund marketing or cushion a slow month.
This guide is for retailers, distributors, makers and service businesses that carry parts. You'll learn to measure turnover and days on hand, sort stock by what actually matters, calculate the cost of slow inventory, set reorder points, and free up cash without running out of your best sellers.
Why inventory is really a cash problem
When you buy inventory, cash leaves your bank account and turns into boxes. It only turns back into cash when those boxes sell and the customer pays. Until then, the money is stuck.
Holding inventory also costs money every month, even if you never think about it. Those carrying costs include:
- Financing: interest on the credit line or the return you give up on the cash
- Storage: the share of rent, shelving and utilities the stock takes up
- Insurance on the value of stock
- Shrinkage: theft, damage and miscounts
- Obsolescence: styles change, models update, products expire, and you end up marking down
Too little inventory costs you too, in lost sales and rush shipping. The goal isn't the least inventory possible. It's the right amount in the right items.
How to measure inventory: turnover and days on hand
- Inventory turnover = cost of goods sold for the year ÷ average inventory value (at cost)
- Days on hand = 365 ÷ inventory turnover
- Average inventory = (starting inventory + ending inventory) ÷ 2, or better, the average of monthly counts
Turnover tells you how many times you sell through your stock in a year. Days on hand translates that into how long a typical item sits before it sells. Always use cost, not retail price, on both sides of the formula. Our explainer on inventory turnover covers the measure in more depth.
Worked example: an independent bike shop
Suppose a hypothetical bike shop had $420,000 in cost of goods sold last year and carried an average of $140,000 of inventory.
- Turnover: $420,000 ÷ $140,000 = 3.0 times a year
- Days on hand: 365 ÷ 3.0 ≈ 122 days
The average item sits for about four months. Now break it down by category:
| Category | Annual COGS | Average inventory | Turnover | Days on hand |
|---|---|---|---|---|
| Complete bikes | $250,000 | $95,000 | 2.6 | about 139 |
| Parts and tubes | $90,000 | $18,000 | 5.0 | 73 |
| Accessories | $60,000 | $17,000 | 3.5 | about 103 |
| Apparel | $20,000 | $10,000 | 2.0 | about 183 |
| Total | $420,000 | $140,000 | 3.0 | about 122 |
Now the picture is clearer. Parts move quickly. Apparel sits for half a year. And complete bikes hold most of the money: $95,000, or about two-thirds of all inventory.
Suppose the owner sets a target of 3.5 turns. At the same sales, average inventory would need to be $420,000 ÷ 3.5 = $120,000. That frees $20,000 of cash, and days on hand fall to about 104. Most of that improvement should come from bikes and apparel, not from parts, which already move well. To run your own numbers, use our inventory turnover calculator.
Sort your stock with ABC analysis
Not every item deserves the same attention. ABC analysis ranks items by how much money they move each year (annual units sold × unit cost):
| Class | What it includes | How to manage it |
|---|---|---|
| A | The relatively few items that make up most of your annual cost of sales | Count often, forecast carefully, reorder frequently in smaller quantities, negotiate hard on price |
| B | Middle items with moderate value and volume | Review monthly; standard reorder points |
| C | Many low-value items that make up a small share of cost | Keep simple: larger, less frequent orders; minimal tracking effort |
To build it, export a year of sales by item with unit cost, calculate annual cost for each, sort from highest to lowest, and draw lines where cumulative cost reaches roughly the top 70–80% (A) and the next 15–20% (B). The exact cutoffs matter less than the habit of focusing effort where the money is.
What to do with dead stock
Run a report of items with no sales in 180 days. Suppose the bike shop finds $22,000 (at cost) of slow-moving stock: last year's apparel colors, accessories for discontinued models, and a few high-end bikes.
First, estimate what holding it costs. Suppose the owner estimates carrying costs as 10% for financing, 2% for shrinkage and damage, 4% for storage and insurance, and 6% for obsolescence, a total of 22% a year. That's an illustrative estimate; build yours from your own costs.
- Annual cost of holding the dead stock: $22,000 × 22% = $4,840
Next, test a markdown. If the shop normally prices at a 45% gross margin, the stock's full retail value is about $22,000 ÷ (1 − 0.45) = $40,000. Selling it at 30% off brings in $40,000 × 70% = $28,000. That's still $6,000 above cost, and it turns $22,000 of shelf space into cash now.
Options for dead stock, roughly in order of preference:
- Bundle it with fast sellers or use it as a gift with purchase.
- Mark it down in stages, with a deadline for each step.
- Return it to the supplier, even with a restocking fee.
- Sell it through a liquidation or clearance channel.
- Donate it, and ask your CPA about the tax treatment.
Then find out why it happened. Dead stock usually traces back to over-ordering on optimism or minimum order quantities. Fixing that is cheaper than clearing it later.
Set reorder points so you order less, more often
A reorder point tells you when to place an order so new stock arrives just before you run out.
- Reorder point = average daily sales × supplier lead time in days + safety stock
- Safety stock = extra units to cover demand spikes or late deliveries
The bike shop sells about 6 inner tubes a day. The supplier takes 7 days to deliver, and the owner wants 3 days of safety stock.
- Reorder point: (6 × 7) + (6 × 3) = 42 + 18 = 60 tubes
When stock hits 60, reorder. Set higher safety stock for A items that customers expect you to have, and lower for C items. Review the numbers quarterly, since sales and lead times change. For seasonal businesses, our guide to inventory forecasting shows how to adjust reorder quantities ahead of busy periods.
Common inventory mistakes
- Buying big for a discount you can't afford. A volume discount that doubles your stock can cost more in carrying costs and cash strain than it saves. Compare the discount with your carrying cost rate.
- Managing all items the same way. Spending as much time on $2 items as on $2,000 items wastes attention. Use ABC analysis.
- Ignoring slow movers until they're dead. Review aging stock monthly and act at 90 days, not 18 months.
- Trusting system counts without checking. Records drift. Cycle count A items monthly and do a full count at least yearly.
- Measuring turnover at retail value. Mixing cost and retail distorts the ratio. Use cost on both sides.
- Cutting inventory across the board. Running out of best sellers loses customers. Cut slow categories and protect fast ones.
Inventory is one of the three pieces of your cash conversion cycle, alongside how fast customers pay you and how fast you pay suppliers. Improving it has a direct effect on cash.
Where AI can help
AI tools are well suited to the analysis. Export item-level sales and inventory from your point-of-sale or inventory system and ask an assistant to calculate turnover and days on hand by category, run an ABC classification, and list items with no sales in 90 or 180 days. It can also calculate reorder points for your top items from daily sales and lead times you supply.
Check its output against what you know. It won't know that a slow item is a deliberate special order, that a supplier's lead time just doubled, or that a new model launch will make current stock obsolete next month. Use it to find the questions; answer them yourself.
Frequently asked questions
What is a good inventory turnover ratio?
It varies widely by industry. Businesses selling perishable or fast-moving goods turn inventory far more often than those selling durable, high-value items. Compare against your own history and similar businesses, and look at turnover by category rather than one overall figure.
How often should I count inventory?
Count high-value (A) items monthly or even weekly through cycle counts, and do a full physical count at least once a year. Counting a few items at a time on a rotating schedule is easier than shutting down for a full count.
How much safety stock should I keep?
Enough to cover typical variation in demand and delivery times for items customers expect you to have. Start with a few days of average sales, then adjust based on how often you run out or end up with excess.
Is it better to have too much or too little inventory?
Neither. Too much ties up cash and risks markdowns; too little loses sales and customers. Aim for high availability on your top sellers and lean stock on slow, low-value items.
Key takeaways
- Inventory is cash on a shelf; it costs money every month you hold it.
- Measure turnover and days on hand by category, using cost values.
- Use ABC analysis to focus attention on the items that tie up the most money.
- Calculate the carrying cost of slow stock and clear it before it becomes dead stock.
- Set reorder points from daily sales, lead time and safety stock, and review them quarterly.
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