Inventory Turnover

The numerator must be measured on a cost basis, not a selling-price basis, because inventory itself sits on the balance sheet at cost. Cost of goods sold and average inventory therefore speak the same language, and the resulting figure is a genuine count of how many times the stock pile is cycled through during the period.

Average inventory is normally the simple mean of opening and closing balances, which assumes the balance moves smoothly through the year. For seasonal businesses that assumption breaks down: a toy retailer measured on a December-to-December average understates the inventory it actually carried in autumn. Where interim data exist, averaging quarterly or monthly balances produces a more faithful denominator. When only a closing balance is available, the ratio can still be computed, but the analyst should note that it is a point-in-time approximation.

Turnover is easier to interpret once inverted into time. Dividing the number of days in the period by inventory turnover yields days of inventory on hand, the average shelf life of a unit of stock. A turnover of four implies roughly ninety days of inventory; a turnover of twelve implies about thirty. Analysts often prefer the days form because it is directly comparable to the payment terms a firm negotiates.

Days of inventory on hand is also the first term of the cash conversion cycle: add days of sales outstanding from receivables, subtract days of payables outstanding, and the result estimates how long cash is locked into working capital before it returns. Shortening inventory days therefore has a direct funding consequence, releasing cash that would otherwise require short-term borrowing or equity to finance.

A rising ratio can mean disciplined procurement and strong demand, or it can mean the firm is running too lean and losing sales to stockouts. The corroborating evidence is revenue growth: turnover improving alongside sales growth that matches or beats peers supports the efficiency story, while turnover improving as sales stagnate suggests inventory has been cut below the level the business needs. Gross margin adds a second check, since a firm can inflate turnover by discounting aggressively.

Accounting events distort the ratio too. A large write-down reduces the carrying amount of inventory and inflates cost of goods sold in the same period, pushing turnover up for reasons that have nothing to do with operating improvement. Conversely, deliberate stockpiling ahead of an anticipated price rise or supply disruption depresses turnover while being economically rational.

At Level I, candidates should be able to extract cost of goods sold from the income statement and inventory from two consecutive balance sheets, compute the ratio, convert it to days of inventory on hand, and embed that figure in the cash conversion cycle. The same fluency is expected in reverse: given days of inventory on hand and cost of goods sold, back out the average inventory balance.

Comparability work matters as much as arithmetic. Where one firm reports under LIFO and a peer under FIFO, a LIFO reserve disclosure allows the LIFO firm's inventory to be restated upward and its cost of goods sold adjusted, placing both on a common basis before the ratios are ranked. Comparisons should stay within an industry and, ideally, within a similar business model, since the appropriate level of stock is set by product perishability, customer expectations and sourcing lead times.