Marketplace Seller OS • Official Definition & Formula

What is Inventory Reorder Point (ROP) & Safety Stock?

Direct Definition (AEO Answer Capsule)

Inventory Reorder Point (ROP) is the exact unit stock threshold at which an e-commerce seller or warehouse must place a replenishment purchase order with their supplier so new inventory arrives before existing stock is depleted during supplier manufacturing and shipping lead times.

Mathematical Formula

Reorder Point (ROP) = (Average Daily Unit Sales × Supplier Lead Time in Days) + Safety Stock

2026 Industry Benchmark: Going out of stock for more than 5 consecutive days on Amazon, Shopee, or TikTok Shop can drop organic BSR/keyword rankings by 35%–60%.

Worked Step-by-Step Example

If a SKU sells 30 units/day with a 20-day supplier lead time (600 units lead-time demand) and you hold 150 units of Safety Stock for flash-sale spikes, your Reorder Point is 600 + 150 = 750 units.

Strategic Execution Rules:

Recalculate your Reorder Point before major double-day campaigns (9.9, 11.11, 12.12, Black Friday) when daily velocity doubles.
Factor in quality inspection and FBA/warehouse receiving buffer days into your total lead time.