The Inventory Performance Index is a score from 0 to 1,000 that Amazon assigns to FBA sellers on a Professional plan, and it moves on four things: how much excess inventory you hold, your 90-day sell-through rate, how much stranded inventory sits without an active offer, and whether your replenishable products stay in stock. Amazon describes all four on its own seller blog ("What is the FBA Inventory tool?", sell.amazon.com, May 2025). Falling below Amazon's cutoff costs you storage capacity, and the units that drag the score down are the same units that cost you storage fees, aged-inventory surcharges, and tied-up cash in the books.
Amazon's blog post spells out what the score reads. The four inputs below are quoted or paraphrased from it.
Excess inventory. Amazon treats a product as excess when you hold more than 90 days of supply against customer demand. Every unit past that line counts against you, and it also counts toward monthly storage.
Sell-through rate. Amazon defines it as units sold and delivered over the past 90 days divided by the average number of sellable units in fulfillment centers over the same window. A 90-day rolling figure, so one bad month lingers for a quarter.
Stranded inventory. Units in an Amazon fulfillment center with no active offer. Customers cannot buy them, Amazon still charges storage on them, and the score treats them as a listing problem you have not fixed.
In-stock rate. How well you keep replenishable ASINs available. Stockouts on products that sell hurt the score and the sales line at the same time.
Two more details from the same post matter for what follows. Amazon calculates inventory age on a first-in, first-out basis across the whole fulfillment network, and you only get a score at all if you hold a Professional selling plan, have recent activity, and have inventory in an Amazon fulfillment center.
Amazon does not publish the score cutoff on its public seller pages. The number lives in the Inventory Performance dashboard inside Seller Central, and it has moved more than once since the score launched. This article quotes no cutoff for that reason. Check the dashboard for the figure that applies to your account this quarter.
What sits below the line is a capacity problem. Amazon's FBA page (sell.amazon.com/fulfillment-by-amazon) describes restock limits as the mechanism that determines how much inventory you can ship into the network, and notes that exceeding a restock limit can raise your storage costs. The practical effect for a seller under the cutoff: less room to send in the products that are selling, at the moment you most need to send them in, because the products that are not selling are occupying the space.
The score also lags. Amazon says its IPI accounts for seasonal fluctuations and rewards long-term performance, which is generous when you have a bad month and punishing when you try to fix a bad quarter in three weeks.
Illustrative numbers. Take a seller with 40 FBA SKUs, and look at one of them, a set of ceramic planters.
Sell-through. 300 divided by 1,100 equals 0.27, or 27 percent for the 90-day window. For a seller whose catalog as a whole turns at 60 percent, this SKU is a drag.
Days of supply. 300 units over 90 days is 3.33 units a day. 1,200 on hand divided by 3.33 equals 360 days of supply. Amazon's excess line is 90 days. Ninety days of supply at this velocity is 300 units, so 900 of the 1,200 units are excess by Amazon's definition.
Storage on the excess. 900 units times 0.05 cubic feet equals 45 cubic feet. Amazon charges storage monthly on the daily average cubic feet your inventory occupies, with higher seasonal rates in the holiday months (sell.amazon.com FBA fees guide, July 2026). This article does not quote a per-cubic-foot rate because the schedule changes; at an illustrative $0.80 per cubic foot, the excess alone costs $36 a month, and more in Q4. Small on one SKU. Multiply across a catalog.
The aged surcharge. Amazon charges an aged-inventory surcharge monthly on units stored more than 181 days (sell.amazon.com/fulfillment-by-amazon). At 360 days of supply and FIFO aging, half of these units will cross 181 days before they sell, and the surcharge stacks on top of monthly storage.
Cash. 900 excess units at $6.20 is $5,580 of landed cost sitting on a shelf in an Amazon building, paid for months ago, earning nothing.
Now put the SKU back into the catalog. If the other 39 SKUs hold 6,800 units and sold 5,400 in 90 days against an average of 6,500 sellable, catalog sell-through without the planters is 5,400 divided by 6,500, or 83 percent. With the planters included: 5,700 divided by 7,600, or 75 percent. One SKU knocked eight points off the catalog's sell-through and added 900 units of excess. That is how a score falls: one or two products, held too long, while the rest of the catalog behaves.
The score is Amazon's view. The ledger has its own.
The 1,200 units sit on the balance sheet as inventory at FIFO cost, $7,440. Nothing about that line tells you 900 of the units are excess. An inventory aging report does, when the system tracks inventory by warehouse and by age and can show you the value on hand in 0 to 90, 91 to 180, and 181-plus day buckets. Amazon's aging is one input; your own receiving dates are the other, and the two disagree whenever a shipment sat at your 3PL before it went inbound.
Monthly storage and the aged surcharge arrive as fee lines inside settlements. If the settlement posts as one lump to the bank, those fees vanish into "Amazon fees" and never attach to the planters. Reconciled at the transaction level, they post to their own accounts against the SKU, and the SKU's contribution margin drops to reflect them. That is when a product that looked like it earned 22 percent starts showing 14 percent, and the aging report and the P&L tell the same story from two directions. Aging inventory on Amazon works through the fee side in more detail.
The last stop is the write-down. Units that will not sell at full price in a reasonable window are worth less than $6.20 each, and a CPA will ask you to say so. The inventory aging report predicts write-offs before they land; the IPI score is Amazon telling you the same thing from the outside, three months late.
Four options, and the score, the fee schedule, and the books all point the same way.
Run the four against each other with numbers, not instinct. The already-paid $6.20 is sunk. What matters is the cash each path returns from here, net of the storage and surcharges each path incurs.
Doing that arithmetic for one SKU takes ten minutes. Doing it for 40 before the Q4 storage rates arrive is an afternoon, and most sellers skip it. Crunch, the analytics AI inside ConnectBooks, answers "which products should I hold, discount, liquidate, or remove ahead of Q4 storage fees" from your reconciled data: it treats paid COGS as sunk, weighs future storage, aged-inventory fees, expected sell-through, selling fees, and expected cash recovery, and ranks each SKU. It cannot see a promotion you have not entered or a supplier delay you have not told it about, and it does not create the removal order. It gives you the ranked list. The decision, and the Seller Central login, stay with you.
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