Stockout (Out of Stock)

A stockout happens when demand meets an empty shelf: the product page shows "sold out", the size is greyed out, or the product disappears from listings. Online, partial stockouts are common: a dress may be in stock in two sizes out of six, which for most shoppers means it is out of stock.

Stockouts are a long-standing retail problem. A 2002 worldwide study by Gruen, Corsten and Bharadwaj for the grocery trade bodies FMI, GMA and CIES (funded by Procter & Gamble) put the world average out-of-stock rate at 8.3 percent, according to FMI's announcement of the study. That figure comes from grocery and consumer-goods stores in 2002; treat it as an order of magnitude, not a benchmark for ecommerce today.

What shoppers do next decides who gets the sale. In the same 2002 study, as tabulated in a 2011 University of Regensburg working paper (Helm and Hegenbart), 31% of shoppers facing a stockout switched to another store, 26% switched brand, 19% chose another item of the same brand, 15% postponed and 9% did not buy at all.

For an ecommerce brand, that makes a competitor's stockout one of the cheapest opportunities there is. While their best seller is out of stock, shoppers who searched for it are looking for an alternative, and an ad, a product listing or a small offer on your comparable product reaches them at the right moment. When the competitor restocks, the window closes.

Your own stockouts are the mirror image: they send shoppers to competitors, and some do not come back.

This example is hypothetical. An activewear brand sees that a competitor's best-selling leggings are out of stock in the three most common sizes for nine days. The brand moves budget to its own comparable leggings for those days and features them on its homepage. When the competitor's sizes come back, it moves the budget back.

The decision depended on knowing the dates. A stockout discovered after the restock is history, not an opportunity.

1. Track stock at product and size level. A product that is "in stock" in one rare size is effectively sold out.

2. Record the dates. Start and end dates show how long the window lasts and whether stockouts repeat at the same time each season.

3. Watch for removals too. A product that disappears from the catalog may be discontinued rather than sold out.

4. Act within the window. RivalSweeper tracks stock status on supported websites, along with catalog changes such as removed products, and checks each monitored competitor site daily, so a change is known within 48 hours. Its ad tracking also flags competitors' Meta ads that land on broken, sold-out or ended-offer pages.