Stockouts rarely arrive without warning. The warning is usually sitting in the data three weeks earlier, unread.
The three numbers that matter
- Cover — how many days of demand your current stock represents. Not units on hand. Days.
- Velocity trend — whether an item is accelerating or slowing. An item with 40 days of cover and rising demand is more urgent than one with 20 days and falling demand.
- Lead time gap — cover minus supplier lead time. When that number goes negative, you are already too late.
Why unit counts mislead
A warehouse report showing 800 units feels reassuring. If you sell 200 a week, it is four weeks of cover. If your supplier takes six weeks, you have a problem that a units-on-hand report will never show you.
Building the early warning
The useful version is a single ranked list: every SKU where lead time exceeds cover, sorted by revenue at risk. Not a chart — a list of things to act on this week.
That one view replaces most of what an inventory report usually contains, and it is the thing buyers actually open on a Monday morning.