What it tells you
Days of Supply (DOS) tells you how many days of upcoming demand your available inventory will cover before you run out. If a product has a DOS of 12, you have roughly twelve days of selling left at the expected pace of demand, based on the inventory you can actually use to meet it. It appears as two rows on the Supply planning grid: DOS - start (the coverage at the start of the period) and DOS - end (the coverage at the end, after that period’s demand and supply play out). Watching both tells you whether your buffer is growing or shrinking across the period. DOS is a continuous forward simulation. Starting from the selected inventory point, Spherecast consumes the actual forecast in each future period until the first moment demand can no longer be fulfilled. Unequal future demand therefore matters: a high-demand week uses inventory faster than a low-demand week. Inventory losses are kept separate from demand. Expirations, discontinuation disposals, and transfer departures reduce available inventory, but they do not inflate the demand rate used beyond the forecast horizon. For an internal transfer, inventory leaves the network at departure and becomes available again at arrival. If the remaining network stock cannot cover demand during that in-transit interval, DOS stops at that availability gap. Supply Planning treats DOS as a snapshot at each grid point. Inventory and receipts that have already occurred by that point are reflected in Available, while future external supply after that point is not assumed by DOS. Stored product and warehouse coverage also offers a separate with inbound value; that version uses the same forward simulation but includes allowed future receipts. Overall DOS is calculated from total network inventory and total network demand; it is not the sum of the warehouse DOS values. Days are a duration, not an inventory quantity, so adding them would double-count calendar time. When the network contains exactly one warehouse, the overall and warehouse-specific DOS use the same inputs and therefore match. The network boundary is shared by Supply Planning and stored product coverage. Supplier warehouses without their own sales or production demand are outside the boundary, so their stock and transfers into the network are external supply. If a supplier-mapped warehouse itself carries production demand, its operational role wins: it is included as a Consumable warehouse. This same boundary controls starting stock, demand, losses, and whether a transfer is internal or external. The expanded Available breakdown can still show physical stock in excluded buckets; that stock remains visible for follow-up but does not inflate DOS.How to read it
DOS is color-coded so you can scan a product’s health at a glance. By default the color keys off your available inventory compared with your safety stock (the buffer you want to keep on hand) and your excess threshold (the top of the healthy range).
There is also a simpler days-based fallback where a very low number of days shows red and a very high number shows purple, used when the inventory-based coloring does not apply.
Where DOS cannot be computed, you will see n.a. For example, after a product’s discontinuation date there is no forward demand to cover, so the value is not available.
What to do about it
- Red or orange (low coverage): you are at or heading toward a stockout. Order now, or expedite an open order, to rebuild the buffer before it runs dry.
- Green: healthy, no action needed.
- Purple (excess): you are overstocked. Consider deferring or reducing incoming orders, or transferring the surplus to a location that needs it.
Example
A product shows DOS - start of 6 in orange. Your safety stock target is about 10 days of coverage, so 6 days sits below the buffer you want. That orange cell is your cue to pull in supply before the buffer erodes further. If the next period showed purple at 40 days, you would instead look to slow orders down.Tip: DOS and WOS (Weeks of Supply) measure the same thing on different scales. Pair DOS with Available to see the inventory behind the number, and check Shortage when coverage drops to zero.