Overview

Amazon's inventory supply metrics help FBA sellers monitor their stock levels and maintain healthy inventory performance. This reference covers frequently asked questions about how the days of supply metric works, which SKUs to prioritize when taking corrective action, and which ASINs are exempt from performance calculations. For sellers enrolled in or flagged by the Automated Storage Balance (ASB) program, understanding these details is essential to avoiding excess inventory fees and maintaining strong account health.

Key Points / What Sellers Need to Know

• Days of supply is FBA-only — The metric exclusively considers inventory stored within Amazon's fulfillment network. Seller-fulfilled inventory housed in your own warehouse or through third-party logistics providers does not factor into the calculation.
• Prioritize high-sales SKUs first — When multiple SKUs need attention, Amazon recommends starting with those flagged in ASB program communications, then moving to SKUs with the highest sales volume to maximize business impact.
• Several ASIN types are exempt — Oversize and non-standard size products, auto-replenished items, low-volume ASINs, and certain returned or refurbished products are excluded from performance calculations.
• Historical tracking is available — Sellers can view their historical days of supply data through the FBA Inventory dashboard in Seller Central, allowing them to spot trends and take proactive action.
• Regular monitoring is recommended — Amazon advises checking your days of supply metrics on an ongoing basis rather than waiting for program notifications to arrive.

How the Days of Supply Metric Works

The days of supply metric measures how many days your current FBA inventory will last based on recent sales velocity. It is calculated using only the inventory physically stored in Amazon's fulfillment centers, which means any stock you fulfill yourself from your own warehouse or through merchant-fulfilled channels is completely excluded from this figure. This is an important distinction for sellers who use a hybrid fulfillment strategy, as your FBA performance score will only reflect what Amazon is storing and shipping on your behalf. The metric helps Amazon and sellers alike identify when stock levels are either too high, leading to long-term storage fees, or too low, risking stockouts that hurt sales rank and the Buy Box.