How to Predict Shopify Stockouts Before They Kill Your Growth

The Real Cost of Running Out of Bestsellers

When a hero SKU sells out, your ad spend keeps driving visitors to a 'Sold Out' button. Most brands calculate lost revenue by multiplying out-of-stock days by average daily sales, but the true cost includes customer acquisition erosion and long-term brand equity damage.

Step 1: Calculate Variant Sales Velocity

Never calculate velocity at style level. A t-shirt selling 30 units a day might sell 18 in Medium, 8 in Large, and 4 in Small. Track daily units sold per individual SKU variant over 7-day, 30-day, and 90-day moving windows.

• Isolate SKU-level daily velocity
• Account for recent promo or paid traffic spikes
• Separate recurring core basics from limited seasonal drops

Step 2: Add Total Lead Time (Production + Transit + Docking)

Supplier lead time is rarely just manufacturing time. Always include fabric sourcing, factory production, ocean/air shipping, customs clearance, and warehouse receiving. If factory lead time is 21 days and ocean transit is 14 days, your total lead time is 35 days.

Step 3: Set Your Reorder Trigger Point

Reorder Point = (Daily Sales Velocity × Total Lead Time in Days) + Safety Stock. When variant inventory drops below this threshold, issue a purchase order immediately.