Lumina

Weeks of supply

How many weeks of forward demand the current stock-on-hand will satisfy — the weekly-cadence equivalent of days of cover, used in retail and wholesale.

By Oana Bradulet

Weeks of supply (WOS) measures how many weeks of forward demand your current stock-on-hand will satisfy at the current sell-through rate. It's the weekly-cadence sibling of days of cover, preferred in industries that plan and report on weekly cycles — retail buying, wholesale, fashion, FMCG.

Weeks of Supply = Stock on hand / Average weekly demand

If a SKU has 800 units on hand and is selling 100 a week, weeks of supply = 8. The current stock will run out in 8 weeks at current sell-through.

Why weekly cadence matters

Most retail and wholesale planning runs on weekly cycles:

  • Buying decisions made Mon-Tue based on previous week's sell-through
  • Replenishment orders cut weekly
  • Supplier shipments arriving in week-stamped batches
  • Sales reporting cadenced weekly

Days of cover and weeks of supply are mathematically equivalent (just different units), but the metric matches the cadence of the decision. WOS slots into the language of weekly retail planning more naturally than DOC.

Worked example

A wholesale apparel brand has 4,800 units of a SKU on hand. Last 13 weeks averaged 600 units/week of demand.

WOS = 4,800 / 600 = 8 weeks

Compared to a target band of 6–10 weeks for this category, the SKU is in the middle of the range. Holding pattern.

Choosing the demand denominator

Same considerations as days of cover, weekly:

  • Last 4 weeks — most reactive, can swing on noise
  • Last 13 weeks — standard for most categories; smooths short-term variation
  • Last 26 or 52 weeks — useful for seasonal SKUs to smooth cycle effects
  • Forward forecast — best for known seasonal peaks or upcoming promotional periods

Most retail planning uses 13 weeks as the default with manual override for seasonal or promo-affected SKUs.

Target WOS bands

Healthy weeks of supply varies by category and lead time:

  • Fast fashion: target 4–8 weeks
  • Standard fashion: 6–12 weeks; pre-season can be higher
  • FMCG: 4–8 weeks for fast-movers; 8–12 for slower SKUs
  • Beauty / wellness: 6–10 weeks
  • Furniture / homeware: 12–20 weeks because lead times are longer
  • Long-lifecycle goods: 16+ weeks

The general rule: WOS target ≈ supplier lead time + safety period. A SKU with a 6-week lead time should hold around 8–10 weeks of supply right after a delivery, dropping to 2–3 weeks (the safety stock floor) at the next reorder point.

WOS vs DOC vs DIO

The trio of "how many days/weeks of stock?" metrics:

  • Days of Cover — same calculation, daily units, operational
  • Weeks of Supply — weekly units, retail/wholesale standard
  • DIO — backward-looking accounting measure of days of past COGS

WOS and DOC are forward-looking and operational. DIO is backward-looking and financial. All three answer related questions in different languages.

How retail buyers use WOS

In a typical weekly buying review, WOS is the headline number per SKU:

  • WOS < lead time → urgent reorder; may need to expedite
  • WOS < 1.5× lead time → reorder this week; plan normal
  • WOS within target band → no action; let the planning rule fire when it does
  • WOS > 2× target → investigate; markdown candidate or forecast revision needed

The WOS-vs-target ratio is what triggers the buying conversation. Out-of-band SKUs get reviewed; in-band SKUs are left alone.

When WOS misleads

Same traps as days of cover:

  • Recent stockout depresses the demand denominator, inflating WOS artificially
  • Promotion about to start will collapse WOS once the sale traffic arrives
  • Seasonal end-of-season SKU will look healthy on trailing demand but face a demand cliff

For SKUs with strong seasonality or promotional activity, switch to a forward-forecast denominator. The trailing-average WOS is comfortable; the forward WOS reveals the actual exposure.

WOS at the category and channel level

Aggregating WOS up:

  • Category WOS — total category stock / total category weekly demand. Useful for buying budget allocation.
  • Channel WOS — same calc per channel. Often reveals allocation imbalances (D2C overweight while wholesale starves, or vice versa).

A balanced category WOS can hide unbalanced SKU-level WOS. Always look at the distribution, not just the average.

Formula

Weeks of Supply = Stock on hand / Average weekly demand
Stock on hand
= Current sellable units (excludes damaged, allocated, in QC)
Average weekly demand
= Recent rolling average — typically 13-week trailing for stable, forecast-based for seasonal

Worked example

Wholesale apparel brand has 4,800 units of a SKU. Last 13 weeks averaged 600 units/week. WOS = 4,800 / 600 = 8 weeks. Against a target band of 6–10 weeks for this category, the SKU is mid-range — holding pattern.

Common mistakes

  • →Using a denominator that includes a recent stockout. The depressed demand average inflates WOS, hiding the real exposure.
  • →Reporting one WOS number per SKU when the SKU is sold across multiple channels with different sell-through rates.
  • →Missing the forward forecast on seasonal SKUs. Trailing average WOS can look healthy heading into a demand cliff.
  • →Treating the target WOS as static. Targets should track lead time and supplier reliability — both of which change.

How Lumina handles weeks of supply for scaling brands

Lumina calculates weeks of supply against your demand forecast, so the number reflects how your sales are shifting — one comparable measure across every SKU, showing what's healthy, what's overstocked, and what's running short relative to its lead time.

Frequently asked questions

What is weeks of supply?
Weeks of supply (WOS) is how many weeks of forward demand your current stock-on-hand will satisfy at current sell-through. Stock on hand divided by average weekly demand. It's the weekly-cadence equivalent of days of cover.
How do I calculate weeks of supply?
Weeks of Supply = Stock on hand / Average weekly demand. The denominator is usually the trailing 13-week average for stable SKUs, or the forward forecast for seasonal and promo-affected ones.
What's a good weeks of supply target?
Roughly: lead time + safety period. Fast fashion: 4–8 weeks. Standard fashion: 6–12. FMCG fast-movers: 4–8. Furniture: 12–20 (longer lead times). The right target tracks the SKU's lead time, not a single business-wide number.
What's the difference between WOS and days of cover?
Mathematically equivalent — just different units. Days of cover uses daily demand; WOS uses weekly. Pick the cadence that matches your planning rhythm. Retail and wholesale use WOS; daily replenishment teams often prefer days of cover.
How is weeks of supply different from DIO?
WOS is forward-looking and operational (current stock vs expected demand). DIO is backward-looking and financial (average inventory vs past COGS). WOS reacts immediately to changes; DIO smooths over the period. Use WOS for daily decisions, DIO for financial reporting.

Related terms

Days of cover

How many days of forward demand the current stock-on-hand will satisfy at the current sell-through rate — the operator-friendly view of inventory health.

Inventory turnover— Inventory Turnover Ratio

How many times you sold through your average inventory over a period — usually a year.

Sell-through rate

The percentage of an inventory batch sold within a defined window — the standard measure of whether a buy worked.

Reorder point— Reorder Point (ROP)

The stock level at which you trigger the next purchase order, calculated to land replenishment before you run out.