Overview

Amazon's Inventory Supply Metric is a brand-level performance indicator that measures whether FBA sellers are maintaining adequate stock relative to customer demand. The metric evaluates inventory levels using historical days of supply, comparing both 30-day and 90-day windows to determine whether products are sufficiently stocked. Sellers who fall short of Amazon's benchmarks may see degraded delivery speeds and reduced distribution across fulfillment centers, ultimately impacting customer experience and sales.

Key Points / What Sellers Need to Know

• Brand-level aggregation — The Inventory Supply Metric is calculated across all of a seller's ASINs within a brand, not at the individual product level. This means a few poorly stocked items can drag down overall brand performance.
• Days of supply threshold — Amazon uses a 28-day threshold as the dividing line. ASINs with more than 28 historical days of supply are considered well-stocked, while those below may indicate inventory shortfalls.
• Dual time windows — The metric compares both 30-day and 90-day historical periods and takes the greater of the two values, ensuring that both recent and longer-term supply patterns are captured.
• Parent-ASIN calculation — Days of supply is calculated at the parent-ASIN level, meaning all child variations (sizes, colors, etc.) share the same historical days of supply figure.
• Seller-specific data — Only your own inventory units and shipped units factor into the calculation. Competitor inventory has no bearing on your metric.
• Low inventory impacts fulfillment — When sellers carry insufficient stock, Amazon cannot efficiently distribute products across its network, which can result in slower delivery times for customers.

How the Metric Is Calculated

The Inventory Supply Percentage is calculated by dividing the total on-hand inventory for well-stocked ASINs (those with more than 28 historical days of supply) by the total on-hand inventory across all ASINs. The result is expressed as a percentage that reflects how much of your FBA inventory is adequately stocked relative to demand.