What is Days Sales of Inventory (DSI)?

Why It Matters

DSI matters because inventory sitting unsold is cash a business can't use anywhere else, tied up in warehouse space, storage costs, and the risk of that stock becoming obsolete or needing to be discounted. A rising DSI, even without any change in cost of goods sold, is a direct signal that inventory is accumulating faster than it's selling, which ties up working capital that could otherwise fund growth. Because DSI moves before the cash flow problem becomes obvious on a balance sheet, catching the trend early gives a business time to adjust purchasing or run a promotion before too much capital gets locked up. It's typically read alongside sell-through rate and stockout rate so a team can tell whether a high DSI reflects genuinely slowing demand versus simply having ordered too much of one particular product.

Example

A retailer holds an average inventory worth $300,000 and records $1,800,000 in cost of goods sold over a 90-day quarter. DSI is $300,000 divided by $1,800,000, times 90, which equals 15 days. If DSI climbs to 40 days the following quarter without a change in COGS, that usually means inventory is building up faster than it is selling, a warning sign worth investigating alongside sell-through rate and stockout rate before it ties up more cash than necessary.

Frequently Asked Questions

• How is DSI different from inventory turnover?

  They measure the same underlying efficiency from opposite angles: inventory turnover counts how many times inventory is sold and replaced in a period, while DSI expresses that same relationship as an average number of days. A high turnover corresponds to a low DSI, and vice versa.

• What's considered a good DSI?

  It varies enormously by industry, since perishable goods retailers naturally run a much lower DSI than businesses selling durable or seasonal products. What matters most is whether a company's own DSI is trending up or down relative to its historical norm.

• What causes DSI to increase?

  Overordering relative to actual demand, slowing sales due to demand shifts or increased competition, and poor forecasting ahead of a seasonal transition are the most common causes of a rising DSI.

• How often is DSI typically calculated?

  Most retail and inventory-holding businesses calculate it monthly or quarterly, aligning with their broader financial reporting cycle, though categories with fast-moving or seasonal inventory may track it more frequently.

• How can a business lower a high DSI?

  Running promotions or discounts to accelerate sell-through, adjusting future purchase orders downward, and improving demand forecasting to avoid overordering in the first place are the standard levers used to bring DSI back down.