Weeks of Supply (WOS)
Weeks of Supply (WOS) is a replenishment planning metric that measures how many weeks the current inventory on hand will last at the current rate of sale — used in apparel planning to identify replenishment needs, reallocation opportunities, and overstock risk.
Weeks of Supply (WOS) measures how many weeks the current on-hand inventory will last at the current rate of sale:
WOS = On-Hand Units ÷ Average Weekly Unit Sales
A style with 240 units on hand selling at 40 units per week has 6 weeks of supply. That figure tells the planner how much selling time remains before stockout — and whether to reorder, reallocate, or take no action.
WOS in apparel allocation and replenishment
Weeks of Supply is the primary signal for operational inventory decisions in-season:
Low WOS: A style running at 2–3 weeks of supply is approaching stockout. If there are more weeks remaining in the full-price sell window than the WOS indicates, the style needs replenishment or reallocation from slower-moving doors.
High WOS: A style with 10+ weeks of supply midway through a 12-week sell window is likely to have residual inventory at season end. This is an early markdown risk signal — the style may not sell through at full price within the remaining window.
WOS by door or location: Aggregate WOS can mask imbalance. A style averaging 6 WOS across all doors may be running 2 WOS at one door (heading toward stockout) and 14 WOS at another (heading toward residual). Door-level WOS drives reallocation decisions.
WOS vs Sell-Through Rate
WOS and Sell-Through Rate measure inventory performance from different angles:
| | Weeks of Supply | Sell-Through Rate | |---|---|---| | Measures | Time remaining before stockout | % of inventory sold to date | | Direction | Forward-looking (how long?) | Backward-looking (how much sold?) | | Primary use | Replenishment / reallocation trigger | Hindsight performance assessment |
Both metrics are typically used together in allocation and in-season management.
WOS and the sell window
WOS must be interpreted relative to the remaining sell window. A WOS of 8 is fine if there are 10 weeks of full-price selling left; it represents significant stockout risk if only 4 weeks remain.
Effective WOS monitoring compares current WOS to remaining full-price weeks in the season — not an absolute threshold. A WOS that looks comfortable in February may signal stockout risk in April.
RetailNorthstar tracks Weeks of Supply at the style and door level throughout the season, surfacing both stockout risk (low WOS vs remaining sell window) and residual risk (high WOS with limited time remaining) as actionable signals.