What is Weeks of Supply?

Weeks of supply (WOS) measures how many weeks your current inventory will last if sales continue at their current average rate. It is calculated by dividing on-hand inventory by the average weekly sales rate. A WOS of 8 means you have roughly two months of inventory; a WOS of 2 means you need to reorder urgently. WOS is the weekly equivalent of Days of Supply and is commonly used for merchandise planning and purchasing decisions.

Why It Matters

Weeks of supply provides an intuitive measure that bridges inventory levels with purchasing timelines. Since most purchasing cycles operate on weekly cadences and supplier lead times are often measured in weeks, WOS aligns naturally with buying decisions. It is the standard metric used in retail merchandising and is particularly useful for seasonal planning where you need to ensure sufficient stock for an entire selling season.

How It Works

• Calculation: Weeks of Supply = On-Hand Units ÷ Average Weekly Sales Rate. Use forward-looking projected sales (not just historical) for more accurate planning during seasonal shifts.
• Target Setting: Set WOS targets by product category and selling phase. Pre-season might target 12–16 weeks; mid-season 6–8 weeks; end-of-season 2–4 weeks to minimize end-of-season markdowns.
• Open-to-Buy: WOS feeds directly into open-to-buy planning, determining how much budget remains for new inventory purchases within a category or time period.
• Markdown Triggers: When WOS exceeds targets (especially late in a season), it triggers markdown decisions to accelerate sell-through and free up capital and warehouse space.

How Nventory Helps

Nventory calculates weeks of supply for every product across all locations, updated in real time. The system alerts you when WOS falls below minimum thresholds (reorder urgently) or exceeds maximum thresholds (consider markdowns), helping you maintain optimal stock levels throughout the product lifecycle and selling seasons.