Free tool
Weeks of Supply Calculator
See how long available stock lasts at the rate you enter.
A weeks of supply calculator connects available units with a stated unit-demand rate. It helps you check the depth of a SKU, size or product group without mixing units with inventory value. The result is a stock-cover scenario under your entered rate.
Use stock that is sellable and available after reservations or other commitments. Incoming inventory needs its own timing consideration because an arrival next month cannot cover a shortfall next week. For historical inventory efficiency measured at cost, use the Inventory Days Calculator. The Inventory Planning Calculator brings cover into the wider replenishment decision.
Available units · Entered demand rate · Incoming stock excluded from current cover
Current stock
Use a consistent scope and cost basis for every figure.
The example is illustrative. Replace it with your own figures; results update as you type. Your entries stay in this page until you choose to copy them.
Need help finding your figures in Shopify?
Copy an input checklist for Sidekick. Store reports may not contain every cost or scenario assumption; verify the source and mark missing figures rather than guessing.
Incoming stock
Demand assumption
How this tool works
How stock cover is calculated
Divide available units by weekly unit demand to calculate weeks of supply. Multiply weeks by seven to express the same cover in days. If you start from a daily rate, multiply that rate by seven before comparing it with a weekly figure.
The demand rate is your assumption, not an automatic forecast. Check whether the period behind it includes a promotion, stockout or seasonal change. At zero demand there is no finite depletion time in this model; that is different from evidence that inventory will never sell. Incoming stock is excluded from current cover unless a separate scenario explicitly says otherwise.
Weeks of supply = available units ÷ units demanded per week. Days of supply = weeks of supply × 7.
Separating available stock from the pipeline
If 300 units are on hand and 60 are reserved, 240 remain available. At 40 units per week, current cover is 6 weeks or 42 days. Another 200 units expected later do not change today’s cover; their arrival date must be considered separately.
Your full calculation
| Measure | Result · USD |
|---|---|
| Current weeks of supply | 8 weeks |
| Current days of supply | 56 days |
| On-hand units | 1,000 |
| Reserved on-hand units | 200 |
| Currently available units | 800 |
| Incoming units, excluded from current cover | 300 |
| Hypothetical available units after all incoming arrives | 1,100 |
| Hypothetical cover after all incoming arrives | 11 weeks |
| Entered weekly demand | 100 |
Questions & answers
Understanding your result
How do you calculate weeks of supply?
Divide available, sellable units by the weekly demand rate you want to test. At 250 available units and 50 units per week, cover is 5 weeks. Keep the unit and product scope the same in both inputs.
Should I include reserved or incoming inventory?
Exclude reserved or committed units from currently available stock. Do not add incoming units to current cover without considering their receipt date. A shipment arriving after depletion will not prevent the earlier gap.
What happens when weekly demand is zero?
There is no finite number of weeks to depletion under a zero-demand assumption. The calculator should identify that condition rather than present an ordinary cover number. Check whether zero reflects genuine demand, missing data or a period when the product was unavailable.
Can weeks of supply tell me when to reorder?
It is one input to the decision. Compare demand during supplier lead time with available stock and your chosen buffer, using the Reorder Point Calculator. Also check confirmed arrivals and cash commitments before placing an order.