Days of cover
Days of cover is the number of days current stock will last at the current rate of sale. It is calculated as units on hand divided by average daily unit sales. Ecommerce operators use it to time reorders, flag looming stockouts and expose overstock before it becomes dead stock.
| Units on hand | Sellable units in stock now. Decide, and state, whether in-transit and reserved units count |
| Average daily unit sales | A trailing average (28 days is common) or a forecast rate, per SKU |
Worked example
A single SKU, priced at $50, with a 45-day supplier lead time (example numbers).
If the purchase order is not placed within 15 days, the store runs dry before the next receipt lands. At 9 units a day and $50 a unit, every stocked-out day after that forfeits about $450 of revenue.
What is a good days of cover?
There is no universal day count - cover is only good or bad relative to your lead time. The floor is set by supplier lead time plus a buffer sized to your demand volatility and how often you review stock; anything below that is a stockout being scheduled. The ceiling is set by cash: every day of cover above what lead time and volatility require is money sitting still, and for seasonal or short-shelf-life goods it is also markdown risk. Judge each SKU against its own lead time, not against a quoted number.
Days of cover vs related metrics
| Metric | What it measures | How it differs |
|---|---|---|
| Reorder point | The stock level that triggers the next purchase order | The same decision expressed in units instead of days. Cover says how long the runway is; the reorder point says when to act. |
| Inventory turnover | How many times average inventory converts to sales in a year | Backward-looking and at cost. Days of cover is forward-looking, per SKU, in units. |
| Stockout | Demand arriving with no stock to serve it | The event days of cover exists to prevent - cover below lead time is a stockout with a date on it. |
| Demand forecasting | Predicting the future sales rate | Upgrades the denominator: a forecast rate replaces the trailing average when demand is trending or seasonal. |
Common mistakes
- Averaging across a stockout. Zero-sales days drag the daily rate down and inflate cover exactly when the SKU is in trouble. Exclude out-of-stock days from the average.
- Averaging across a promo spike. A sale week overstates the run rate and triggers over-ordering. Normalise or annotate promotional periods.
- Computing cover at catalogue level. A healthy blended number can hide one SKU at 400 days and another at 4. Cover only means anything per SKU and variant.
- Ignoring committed and in-transit units. Reserved stock is not sellable, and inbound stock changes the reorder decision. State what the on-hand figure includes.
- Ignoring seasonality and planned promotions. Sixty days of cover at today's rate can be twenty at the rate your calendar says is coming.
Frequently asked questions
In Blufire, S7 Inventory computes days-of-cover and reorder timing per SKU on the ABC x XYZ grid, so the SKUs about to run dry and the ones hoarding cash surface in the same view.
Updated July 2026