Glossary term
Days Sales of Inventory (DSI)
Days sales of inventory, or DSI, estimates how many days inventory sits before it is sold.
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What Is Days Sales of Inventory (DSI)?
Days sales of inventory, or DSI, estimates how many days it takes a company to sell through its inventory. It is also commonly called days inventory outstanding or days in inventory.
DSI is an inventory efficiency metric. It helps show whether cash is tied up in inventory for a short or long period before products are sold.
Key Takeaways
- DSI estimates the number of days inventory remains on hand before sale.
- A lower DSI often means inventory turns faster.
- A higher DSI can point to slow-moving stock, overbuying, or weak demand.
- DSI varies widely by industry and product type.
- It should be read with margins, stockout risk, seasonality, and inventory quality.
DSI Formula
A common formula is:
Average inventory is the average inventory balance for the period. Cost of goods sold is used because inventory is usually carried at cost, not selling price. Days in period is commonly 365 for annual analysis.
If average inventory is $1 million, annual cost of goods sold is $6 million, and the period is 365 days, DSI is about 61 days.
DSI is closely related to inventory turnover. Turnover shows how many times inventory is sold during a period; DSI translates that speed into days.
How to Read DSI
DSI pattern | Possible meaning | Watch for |
|---|---|---|
Low DSI | Fast inventory movement | Stockouts or too little safety stock |
High DSI | Slow inventory movement | Obsolescence or weak demand |
Rising DSI | Inventory building faster than sales | Markdowns or cash tied up |
Falling DSI | Inventory selling faster | Better demand or leaner inventory |
Why It Matters
DSI matters because inventory uses cash before it creates cash. Holding too much inventory can increase storage, insurance, financing, spoilage, markdown, and obsolescence costs.
But holding too little inventory can also hurt sales. A low DSI may look efficient, yet still be a problem if customers cannot buy what they want when they want it.
Managers often track DSI by product line to spot stale stock earlier.
Limits and Misunderstandings
DSI is not comparable across every business. Grocery, fashion, auto, pharmaceutical, and heavy-equipment companies can have very different normal inventory cycles.
It can also be distorted by seasonality, supply-chain disruptions, accounting methods, product launches, write-downs, or temporary inventory builds ahead of expected demand.
The Bottom Line
DSI estimates how long inventory stays on hand before sale. It is useful for spotting inventory efficiency, but it should be interpreted with product type, seasonality, margins, and service-level goals.