toolbox
Home / Online Selling & Retail / eBay Reorder Calculator

eBay Reorder Calculator

The eBay Reorder Calculator estimates when to place the next inventory order and how many units to buy. It combines average daily sales, supplier lead time, safety-stock days, current stock, outstanding purchase orders, and a target coverage period.

The tool is designed for sellers who want a simple replenishment rule without building a full forecasting model. It reports the reorder point, projected stock at arrival, urgency, and suggested order quantity. Demand is treated as steady, so seasonal listings or volatile items should use a more conservative safety allowance.

Calculator inputs

units
days
days
units
units
days
Result
—
Suggested reorder quantity
Reorder point—
Inventory position—
Current days on hand—
Projected stock at arrival—
Reorder status—
Coverage after suggested order—

1. Estimate daily sales
Use a recent period representative of expected demand and divide units sold by selling days.

2. Enter lead time
Count calendar days from placing the order until units are available for sale.

3. Choose safety coverage
Add buffer days for demand variation, late suppliers, or receiving delays.

4. Record available and incoming units
Current stock should exclude damaged or committed inventory; incoming stock should include only confirmed orders.

5. Review the reorder point and quantity
Order when inventory position reaches the reorder point, and adjust the suggested quantity for case packs or cash limits.

Reorder point = Average daily sales × (Lead time + Safety-stock days)
Inventory position = Current stock + Incoming stock
Suggested order quantity = max(0, Average daily sales × Target coverage − Projected stock at arrival)

Where:

  • Average daily sales: expected units sold per day
  • Projected stock at arrival: inventory position minus demand during lead time
  • Target coverage: desired days of stock available after replenishment arrives

Assumptions: Demand remains constant and no additional purchase orders arrive beyond the entered incoming stock.

What the result means

The suggested quantity restores projected arrival stock to the selected coverage target.

Use supplier case packs, minimum order quantities, seasonality, and cash constraints to refine the order.

Given:

  • Average daily sales: 2.5 units
  • Lead time: 14 days
  • Safety stock: 7 days
  • Current stock: 60 units
  • Incoming stock: 0 units
  • Target coverage: 45 days

Calculation:
Reorder point = 2.5 × (14 + 7) = 52.5 units. Projected stock at arrival = 60 − (2.5 × 14) = 25 units. Target stock = 2.5 × 45 = 112.5 units. Suggested order = 112.5 − 25 = 87.5, rounded up to 88 units.

Result:
Order approximately 88 units; current inventory is above the 52.5-unit reorder point.

Interpretation:
The stock is not yet below the trigger, but placing an order soon may be reasonable if demand or lead time is uncertain.

Should I use calendar days or selling days?

Use the same day basis for daily sales and lead time. Calendar days are usually simpler when orders can occur every day.

Why is the suggested quantity rounded up?

Inventory is ordered in whole units, and rounding down can leave the target coverage slightly short. Adjust further for supplier case packs.

What does inventory position mean?

It is current sellable stock plus confirmed incoming units. More advanced systems may also subtract backorders or committed units.

How should I handle seasonal demand?

Use a forward-looking daily sales estimate for the upcoming season and increase safety coverage when forecast uncertainty is high.

Is the reorder point the same as the order quantity?

No. The reorder point is the stock level that triggers action; the order quantity is how many units are needed to restore the chosen coverage.