Why fulfillment-program storage isn't unlimited
When you use a marketplace's own fulfillment service (Amazon FBA, Walmart WFS, and similar), you're storing inventory in the platform's own warehouse network — which means the platform, not you, controls how much space you're allotted, and that allotment is commonly tied to how efficiently you're using the space you already have, not just a flat cap.
Amazon's Inventory Performance Index (IPI) approach
Amazon's system scores sellers on an inventory health metric that factors in elements like excess inventory (units far exceeding likely near-term sales), sell-through rate, stranded inventory (unsellable due to a listing or catalog issue), and in-stock rate. A lower score commonly triggers storage capacity limits — meaning that a poor score doesn't just carry a reputational or informational cost, it can directly reduce how much inventory you're allowed to store, at the exact moment you might want to reorder more. This creates a genuine feedback loop worth planning around: overstocking (which lowers the score) can restrict your storage capacity precisely when you're trying to work through that overstock.
Because the score and its exact thresholds are revised periodically, don't anchor planning to a specific number you read somewhere online — check your current score and its component factors directly in your seller dashboard, and treat any external description (including this one) as a guide to the mechanism, not a citation for the current threshold.
Walmart's approach
Walmart's WFS program similarly monitors inventory performance and applies fees or restrictions tied to excess or aged inventory, though its specific mechanics and terminology differ from Amazon's IPI system. Sellers running both programs should treat each platform's inventory health system as genuinely separate — a habit that works to protect your score on one platform doesn't necessarily translate directly to the other's specific rules, so it's worth reviewing each platform's current documentation independently rather than assuming they're equivalent.
Marketplaces without a comparable formal system
eBay, Etsy, and similar marketplaces that don't offer their own large-scale fulfillment-center storage program generally don't have an equivalent formal inventory-health/storage-limit score, since you're typically storing and shipping from your own location rather than the platform's warehouse network. That doesn't mean inventory management matters less there — a stockout still costs you ranking and sales the same way (see How to Prevent and Recover From Stockouts) — it just isn't formalized into a platform-enforced storage cap the way it is on Amazon or Walmart's fulfillment programs.
Protecting your score/standing proactively
Regardless of the specific platform's formula, the underlying behaviors that protect inventory-health standing are consistent:
- Keep sell-through rate healthy by sizing purchase orders against realistic demand forecasts (see Demand Forecasting for Ecommerce) rather than ordering opportunistically in large batches.
- Address aged and excess inventory promptly (see Overstock and Aged Inventory) rather than letting it sit and drag down the score further while also accruing storage fees.
- Fix stranded/unsellable inventory issues quickly — inventory that can't sell due to a listing error or catalog issue commonly counts against inventory health even though it's a catalog problem, not truly an overstock problem.
- Maintain a healthy in-stock rate by managing reorder points properly (see How to Calculate Safety Stock) — since these scores often weigh being frequently out of stock similarly negatively to being significantly overstocked.
If you're already storage-restricted
Prioritize working through your highest-holding-cost, lowest-turnover units first (see Inventory Turnover Explained to identify them), since clearing those tends to improve the underlying score components fastest and frees the most storage capacity per unit cleared. Avoid the instinct to simply order less of everything indiscriminately — a targeted cleanup of the actual problem SKUs is more effective than a blanket pullback that could create stockouts on your healthy, fast-moving SKUs instead.