What days of supply is
Days of supply (DOS) is on-hand inventory divided by average daily demand: how many days your current stock lasts before you run out at the rate it is selling. Weeks of supply (WOS) is the same idea on a weekly clock, which is the unit most CPG planners actually speak in because retailer POS and KeHE Connect report by week. When I ran replenishment for a natural brand, WOS was the number that decided whether I slept, because too little meant stockouts at Sprouts and too much meant a cash-flow problem in a warehouse.
The math is deliberately simple so it stays honest. DOS equals units on hand divided by average units sold per day. WOS equals units on hand divided by average units sold per week. The judgment is not in the formula, it is in the denominator: pick the wrong demand rate and the number lies. If you searched "weeks of supply" because a buyer flagged your inventory as high or low, the rest of this page is the conversion they ran.
How to calculate it
Start with velocity, because DOS and WOS are just velocity turned upside down. Take a granola SKU selling across 220 Sprouts stores.
| Input | Value |
|---|---|
| Units sold per store / week | 6 |
| Store count | 220 |
| Total weekly demand | 1,320 units |
| Average daily demand | 188.6 units |
| On-hand inventory | 9,240 units |
Weeks of supply is 9,240 / 1,320 = 7.0 weeks. Days of supply is 9,240 / 188.6 = 49 days, which is the same 7.0 weeks expressed in days (7.0 x 7 = 49). They are one number in two units, so quote whichever your counterpart speaks. A buyer who lives in WOS does not want a 49 in the cell.
The denominator is where people go wrong. If that granola SKU is about to run a promotion that triples velocity to 18 units per store per week, the honest WOS at promoted demand is 9,240 / (18 x 220) = 2.3 weeks, not 7.0. Same inventory, very different risk. Always state DOS or WOS against the demand rate you actually expect, not the trailing average, especially around a promotion or a seasonal swing.
Target ranges and what they signal
There is no universal target. The right band depends on lead time, shelf life, and how volatile demand is. The working rule is that on-hand supply should cover replenishment lead time plus a safety cushion, and not much more. The table below is the kind of band I planned against for shelf-stable natural grocery; perishables run far tighter and slow imports run looser.
| Weeks of supply | What it usually signals |
|---|---|
| Under 2 | Stockout risk; lead time barely covered |
| 4 to 8 | Healthy band for shelf-stable grocery |
| 10 to 14 | Overstocked; cash tied up, markdown risk rising |
| Over 16 | Dead stock forming; forecast or ordering is off |
Too low is the loud failure. You miss sales you cannot recover and you bruise your on-shelf availability, which retailers score and remember. Too high is the quiet one. The inventory does not disappear, it just sits there absorbing cash, aging toward markdowns, and on a perishable SKU walking straight into spoilage. A WOS creeping up week over week while velocity holds flat is usually the first sign a forecast ran hot and the orders followed it.
Why it matters to a CPG analyst
DOS and WOS are the bridge between a demand forecast and a purchase order. Your demand forecast sets the denominator, your target WOS sets how much cushion you carry, and the two together size the next order. Get the velocity assumption right and the supply number does its job. Get it wrong and you either starve the shelf or drown the warehouse, and both show up in the P&L a few weeks later.
It is also a diagnostic, not just a planning input. When I saw WOS diverge across two retailers for the same SKU, it pointed straight at a problem: one DC over-ordered, or one banner's velocity quietly fell off and nobody adjusted the orders. The number does not fix anything by itself, but it tells you exactly where to look.
Where Scout fits
DOS and WOS only mean something next to real velocity, and that velocity lives in your SPINS or retailer POS data. Scout connects that data so you can track weeks of supply by SKU and by retailer and catch the slow creep before it becomes a markdown. Scout measures and analyzes the velocity side. It does not place your purchase orders, hold your inventory record, or run the replenishment system.
The short version
- Days of supply is on-hand inventory divided by average daily demand; weeks of supply is the same thing on a weekly clock, and CPG planners mostly speak in WOS.
- The formula is trivial; the judgment is in the demand rate you put in the denominator. Use expected velocity, not the trailing average, around promotions and seasonality.
- Too low risks stockouts and lost sales; too high ties up cash and invites markdowns. For shelf-stable grocery, 4 to 8 weeks is a healthy band, with perishables much tighter.