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 on inventory performance and its IPI FAQ.

How is the IPI score calculated?

Amazon does not publish the formula or a range; guides such as Flexport's put the score between 0 and 1,000. Amazon 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:

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, and Amazon updates the rate daily. 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 until February 1, 2027, when it folds into one storage rate, 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 (the threshold was 400 from May 2020, 500 that August and 450 from January 2021, per SPS Commerce), 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.

Do Amazon's 2027 fee changes affect your IPI score?

Not directly, as far as Amazon says. Its 2027 fee overview does not mention IPI, and its IPI pages, read November 6, 2026, describe no change to the score. What changes is what the same stock habits cost. Here are Amazon's lines in one place, for standard-size goods off-peak (January to September), with every fee date in our 2027 guide:

Keep the two clocks apart. Days of supply compares stock with demand, so a large new shipment can count as excess on the day it arrives. Age counts time in the network, so a small leftover lot of a slow SKU can sit well under 90 days of supply and still pass day 181. A weekly report needs both.

Cheaper storage is not the same as a better score. Amazon says ending the storage utilization surcharge will "make it easier to stock up" for high-demand events, and that does lower the bill for stock under six months. Nothing on its IPI pages says units above 90 days of forecast supply stop counting as excess. Amazon does say IPI accounts for seasonality, without saying how much, so we would not assume a large pre-season build leaves the score untouched. That is our reading, not Amazon's wording.

Two details to check on your own account. An FNSKU with 70% or more auto-replenished from AWD pays the lowest storage rate at any age and is exempt from the low-inventory-level fee, but the pages we read do not say how that stock counts for IPI. And Amazon's storage FAQ talks about "SKUs with" IPI scores, while its IPI pages describe one score for overall performance. Sort SKUs by age and sell-through, which FBA Inventory shows per product.

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. Capacity moves faster: a removal order shows in your capacity usage within 24 hours, even while Pending. 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 FBA 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 keep your accounts, your data and the custom code we build; 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.

If excess and aging units are tracked in a weekly spreadsheet, that routine can become a workflow automation project: restock and inventory reports pulled on a schedule, with low-stock alerts and draft purchase orders your buyer approves.