Amazon IPI score (Inventory Performance Index): meaning, drivers and mistakes

The IPI score is Amazon's report card for your FBA inventory: is the stock you keep at Amazon the right stock, and is it selling at a healthy pace? Professional sellers see it on the Inventory Performance dashboard, with the current week's score and past weeks. The rules on this page come from Amazon's US Seller Central help.

How is the IPI score calculated?

Amazon does not publish the formula. It says the score weighs recent and long-term performance, so it moves slowly in both directions. It does publish four drivers, each rated poor, fair, good or excellent:

Driver	How Amazon measures it	What drags it down
Excess inventory	Share of FBA units with more than 90 days of supply against forecast demand	Over-ordering, slow movers
FBA sell-through	Units shipped in 90 days ÷ average units on hand	Too much stock for the sales it supports
Stranded inventory	Share of FBA units with no active offer	Listing errors left unfixed
FBA in-stock rate	Time replenishable ASINs were in stock over 30 days, weighted by units sold over 60 days	Best sellers running out while slow SKUs sit

The formula Amazon spells out in most detail, with a worked example, is sell-through:

FBA sell-through = units shipped in the past 90 days ÷ average units available

The average comes from four snapshots: today, 30, 60 and 90 days ago. A SKU that shipped 270 units, with snapshots of 200, 120, 160 and 240 units, averages 180 on hand and scores 1.5.

In-stock rate is not a direct input. Amazon says it only hurts when popular products keep running out while the stock you still hold is slow, excess or aged.

Why does IPI matter for operations and growth?

Because it helps decide how much you can send in. Amazon says FBA capacity limits for Professional accounts are influenced by IPI, alongside sales history, seasonality, forecasts, new selection, scheduled deals, fulfillment center capacity and lead time. New Professional accounts, active in FBA for less than 39 weeks, get no limit yet. When on-hand stock plus open shipments exceeds the limit, Amazon blocks new shipments. A weak IPI can leave a best seller without room to restock before peak, which is how an inventory metric turns into stockouts.

It also tracks cost. Excess units run up storage fees, units stored 181 days or more add the aged inventory surcharge on top, and Amazon ties a higher IPI to lower storage costs.

Older guides talk about IPI thresholds and score-check weeks. Those belonged to storage volume limits, which Amazon replaced in March 2023 with one monthly capacity limit per storage type. Amazon's IPI FAQ still describes thresholds announced four to eight weeks ahead for storage volume limits, but its capacity limit page names no cutoff score. Treat IPI as a trend that feeds every month's limit, not a line to clear once.

What mistakes drag the IPI score down?

• Sending far more than 90 days of supply at once. A big inbound lifts average on-hand stock, and units beyond 90 days of forecast supply count as excess even if you plan to sell them over 100 days. Because IPI feeds capacity, that drag can cost you space in the months after.
• Leaving stranded inventory for later. Stranded units count against you while they cannot sell.
• Removing stock too late. Units leave the calculation once a removal or liquidation order is placed, but the score catches up slowly. Act weeks before the month you need space for, not after its limit is announced.
• Hiding SKUs as non-replenishable. Even hiding every SKU of an ASIN changes the in-stock rate only, not IPI.
• Chasing the score. Starving best sellers raises sell-through until they stock out. Amazon treats a very high sell-through as a sign of scarce inventory, not a win.
• Forgetting launches. Newly created ASINs are ignored for 90 days. Plan launch quantities for day 91.

How does Growth OS keep IPI healthy?

The base inventory and replenishment module in Ecomsellertool Growth OS tracks days of cover per SKU and channel, sets reorder points from real lead times and drafts POs and shipment plans before you run out. That balance of stock against sales is what the excess and sell-through drivers measure.

IPI is one score for your overall inventory performance, and it is not in the SP-API's FBA inventory reports, so tracking its drivers SKU by SKU is custom work we scope on top of the base. A module like that rebuilds them from reports on your own account: the Manage Inventory Health report (sell-through, days of supply, estimated excess units, age buckets), the Stranded Inventory report and the Restock report. It can then:

1. Rank SKUs by how much each one adds to excess and drags sell-through.
2. Alert on stranded units and route listing fixes to an owner.
3. Cost each excess option side by side: markdown, extra ad spend, Multi-Channel Fulfillment, removal or liquidation.
4. Keep planned FBA shipments inside your capacity limit, with the buffer held in Amazon Warehousing and Distribution (AWD), a 3PL or your own warehouse.
5. Flag inbound shipments that would push a SKU past 90 days of supply.

You own the custom modules we build and your data; the Growth OS base is licensed to you.

Where should you start?

If your capacity limit keeps boxing in best sellers, or excess and stranded units keep growing, start with the free Quick Scan in the Ops Gap Diagnostic. To see the base system first, look at Growth OS.