The eBay Inventory Calculator estimates ending stock, sell-through rate, weeks of supply, and a suggested reorder quantity from opening inventory, additions, sales, and a target coverage period. It is designed for sellers who need a quick view of whether current stock can support expected demand.
The forecast assumes the entered recent sales rate continues. Seasonal demand, listing interruptions, supplier delays, and one-time bulk orders can change actual requirements, so review the suggested reorder against lead time and business risk.
1. Enter opening inventory
Use the on-hand quantity at the start of the measured period.
2. Add received units
Include stock added during the same period.
3. Enter units sold
Use fulfilled sales and do not exceed total available units.
4. Set the period length
Express the measured sales period in weeks.
5. Choose target coverage
Enter the number of weeks you want on hand and review the suggested reorder.
The reorder result is rounded up to a whole unit and assumes demand continues at the measured average rate. It does not separately add supplier lead-time demand or safety stock.
The main result is the estimated number of units remaining at the end of the period.
Use a longer or seasonally comparable sales period when recent demand is unusually volatile.
Given: Opening inventory is 180 units, 40 units are received, 75 are sold over 4 weeks, and target coverage is 8 weeks.
Calculation: Available = 180 + 40 = 220. Ending inventory = 220 − 75 = 145. Weekly sales = 75 ÷ 4 = 18.75. Target stock = 18.75 × 8 = 150. Reorder = 150 − 145 = 5 units.
Result: Ending inventory is 145 units, with a suggested reorder of 5 units to reach eight weeks of supply.
Use fulfilled or recognized sales for the measured period. Exclude canceled orders and add returned sellable units back through your inventory records.
A zero sales rate cannot be used as a denominator. In that case, review demand manually rather than treating supply as infinite.
No. Increase target weeks or add safety stock separately when you need a buffer for uncertainty.
Choose target coverage that is long enough to cover lead time and your desired buffer, or use a dedicated reorder-point model.
No. Sell-through compares units sold with available units for a period. Turnover generally compares cost of goods sold with average inventory value.