Guide
How to calculate days of cover
Updated 13 October 2026
Days of cover is stock on hand divided by the average daily rate of sale. A store holding 24 units of a line that sells 3 a day has 8 days of cover: if nothing new arrives, the shelf will be empty in about 8 days.
The formula
Days of cover
- Stock on hand ÷ average units sold per day
- 24 units ÷ 3 a day = 8 days
Weeks of cover
- Stock on hand ÷ average units sold per week
- 24 units ÷ 21 a week ≈ 1.1 weeks
The calculation is simple. The judgement is in the rate of sale: which days you average over, and what you leave out.
Choosing the rate of sale
- Use a recent window, such as the last four weeks. Too short and one odd day swings the answer; too long and it misses a trend.
- Leave out promotion weeks, or the boosted sales will make normal stock look thin.
- Leave out days the line was out of stock. Zero sales on an empty shelf is not low demand, and counting it understates the rate of sale.
- Work per store and per product. A national average hides the stores that are about to run out.
What a good number looks like
There is no single right answer. The cover a store needs depends on how often it is delivered to, how long an order takes to arrive, and how much demand varies. A line delivered twice a week needs less cover than one delivered every two weeks.
- Too little cover: the shelf will empty before the next delivery arrives. Order now, or expect an out-of-stock.
- About right: enough to reach the next delivery, with a small buffer for a busy day.
- Too much cover: stock is sitting still. It ties up the retailer's money, ages on the shelf, and becomes the first candidate for returns and markdowns.
- No sales at all: cover is infinite. The line is either dead in that store, or the stock is not really there (see phantom stock).
Using days of cover
- Rank stores by days of cover on your best sellers, lowest first, and you have a list of where to send an order or a rep.
- Rank by highest cover and you have the over-supply list: stores to stop ordering for, or to move stock from.
- Suggest an order quantity: the units needed to bring a store back to its target cover, rounded to the pack size.
- Watch cover through a promotion, when the rate of sale jumps and normal stock disappears in days.
How OuterJoin helps
Days of cover is shown for every store and product in our stock health dashboards and store reports. Low-cover lines are flagged and ranked by the sales at risk, and the store reports suggest a pack-rounded order for about two weeks of cover.
Common questions
- Is days of cover the same as stock cover or days of supply?
- Yes. Stock cover, days of supply, days on hand and days of cover all describe the same idea: how long current stock will last at the current rate of sale.
- Should cover be measured at the store or the distribution centre?
- Both, if you can. Store cover tells you whether the shelf will empty; distribution centre cover tells you whether the retailer can refill it.
- What if a line has stock but no recent sales?
- Its days of cover cannot be calculated, and that is a warning in itself. Either the line does not sell in that store, or the stock figure is wrong and the shelf is empty.