IPI (Inventory Performance Index)

The Inventory Performance Index (IPI) is Amazon’s 0-1000 rolling score that measures how efficiently an FBA seller manages inventory across four pillars: excess inventory, sell-through rate, stranded inventory, and in-stock rate. Amazon uses IPI to decide whether to apply FBA storage limits and restock caps on the account.

Why It Matters for Sellers

IPI directly controls how much inventory Amazon lets you send into its warehouses. Accounts with an IPI below 400 face storage limits that can prevent restocks during peak season, capping revenue at exactly the moment when demand is highest. Accounts with an IPI comfortably above 400 keep unlimited storage and full restock flexibility. IPI recalculates weekly, so short-term inventory decisions (removing excess, fixing stranded units, keeping bestsellers in stock) directly move the score within days, not months.

How It Works

  1. Every week, Amazon calculates each of the four pillar scores based on the last 90 days of inventory activity.
  2. The pillars are combined into a single 0-1000 index shown in the Inventory Performance dashboard in Seller Central.
  3. Amazon checks the score at quarterly assessment intervals (roughly every 3 months).
  4. If IPI is below 400 at assessment, Amazon assigns storage limits — a maximum cubic-foot cap by storage type (standard, oversize, apparel, footwear).
  5. If IPI is at or above 400, the account keeps unlimited FBA storage until the next assessment.

Formula and Worked Example

IPI has four weighted pillars. Amazon does not publish exact weights, but the practical impact is roughly:

  • Excess inventory: units with >90 days of supply on hand.
  • Sell-through rate: units sold and shipped over the last 90 days divided by average inventory level.
  • Stranded inventory: FBA units in warehouses with no active buyable listing.
  • In-stock rate: percentage of days your top-selling ASINs were in stock over the last 30 days.

Worked example: A seller has IPI = 380 heading into a quarterly assessment. They:
1. Remove 500 units of aged excess inventory → excess pillar improves.
2. Fix 40 stranded units in one afternoon → stranded pillar recovers immediately.
3. Restock two out-of-stock bestsellers → in-stock rate climbs within a week.

Two weeks later, IPI is 460. The account passes the next assessment with no storage limits applied.

The 400 threshold is the number that matters. Anything above 400 = unlimited storage. Anything below = capped storage until the next quarterly window.

FAQ

What is a good IPI score?

Anything at or above 400 keeps unlimited FBA storage. Amazon suggests targeting 500+ as a comfortable buffer against fluctuations, especially heading into Q4 when demand spikes and holding excess is riskier.

How often does Amazon update IPI?

The IPI score itself updates weekly. Amazon’s storage-limit assessment happens quarterly — roughly every 3 months — based on the score at the assessment date.

How do I improve my IPI score fast?

The fastest levers are: fix all stranded inventory (same-day impact), create removal orders on aged excess (visible within a week), and restock any out-of-stock bestsellers. Sell-through takes longer because it is a 90-day trailing measure.

What happens if my IPI drops below 400?

Amazon applies storage limits per storage type at the next assessment. You can still sell existing inventory, but new inbound shipments are capped at the assigned volume until the score recovers.

How SellerSonar Helps

  • Retail Issues Alerts fire on the listing-level events (suppressions, out-of-stock, offer closures) that hurt the stranded and in-stock pillars of IPI.
  • Product Monitoring tracks stock status and Buy Box across your catalog, so you catch out-of-stock events before they hit the 30-day in-stock-rate window.
  • Real-time alerts let you fix stranded units the same day, protecting the fastest-moving pillar of the IPI score.

Start a free 14-day trial and protect the IPI pillars that Amazon updates fastest.

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