Days of cover converts a stock level into time, which is the unit reordering decisions are actually made in. It is sellable stock divided by average daily sales. The number only means something next to your lead time: cover shorter than lead time means you will run out before a replacement order can arrive.
Work out your days of cover
Nothing is sent anywhere. The calculation happens in this page.
Days of cover = sellable stock ÷ average daily sales
Reading the result
Compare the result against your lead time, because that comparison is the whole point. Cover of 42 days against a 21-day lead time is comfortable. The same 42 days against a 60-day lead time means you are already late.
Days of cover is the most useful number on this page for talking to people who do not think in units. "We have six weeks" lands in a way that "we have 168" does not, and it makes the urgency of a reorder obvious without explanation.
Watch it fall rather than reading it once. A line whose cover has halved in a month is accelerating, and the reorder point calculated on last month's rate is now too low.
When the number looks wrong
The inputs look simple and one of them is routinely wrong.
- Cover looks far too high. Check whether the sales rate includes a period when the product was out of stock. Zero sales during a stockout drag the average down and make cover look generous.
- Cover looks too low on a slow mover. Products selling a few units a month produce noisy daily averages. Use a longer period, or work in weeks.
- Stock on hand does not match the shelf. Use sellable stock, not total. Units allocated to unfulfilled orders, damaged, or reserved for a wholesale order are not cover.
Where the inputs come from
- Sellable stock: what you could sell today. Not total inventory, and not including anything already committed to an order.
- Average daily sales: units over a representative period divided by its days, excluding any stretch where the product was unavailable.
The derivation and a worked example are on the days of cover definition.
Common questions
What is a healthy days of cover?
Whatever comfortably exceeds your lead time, plus a margin. There is no universal figure: 30 days is generous for a domestic supplier and dangerously thin for a 60-day import.
Why is my days of cover misleading after a stockout?
Because the days the product was unavailable sold nothing, which pulls the average sales rate down and makes remaining stock look like it will last longer than it will.
Should I use total stock or sellable stock?
Sellable. Units allocated to unfulfilled orders or reserved for wholesale are not available to cover future demand, and counting them is how stores oversell.
How does this relate to reorder point?
They are the same judgement in different units. Days of cover expresses it as time, a reorder point as a stock level. Cover is easier to discuss; a reorder point is easier to act on.