How is the Amazon IPI score calculated?
Amazon's Inventory Performance Index (IPI) is a rolling score from 0 to 1000 built from four inputs: excess inventory percentage, sell-through rate, stranded inventory percentage, and in-stock rate on FBA. Scores above 400 keep storage limits open; scores below 400 trigger restock limits and higher storage costs.
The four inputs
Excess inventory: percentage of inventory sitting more than 90 days. Sell-through rate: units shipped over the last 90 days divided by average inventory. Stranded inventory: units in FBA that cannot be sold because of a listing issue. In-stock rate: percentage of time popular SKUs stayed in stock.
Why 400 is the threshold
Amazon uses 400 as the cutoff for expanded storage limits. Below 400, you lose access to unlimited FBA storage and pay higher long-term storage fees on aged units.
Fastest ways to raise IPI
Fix stranded inventory (usually a 24-hour fix inside Seller Central), remove excess units with an FBA Removal Order or price-cut promotion, and keep top movers in stock.
- Fix stranded units first (biggest score jump for least effort).
- Run a removal or liquidation on units aged 180+ days.
- Price down units aged 90 to 180 days to accelerate sell-through.
- Set restock alerts on your top 20 SKUs so you never stock out.
Frequently asked questions
How often does IPI update?
IPI recalculates every Monday and reflects the last 90 days.
What happens if IPI drops below 400?
You get restock limits capped on units per SKU or per storage type, and long-term storage fees kick in earlier.
Does removing units instantly raise IPI?
Not instantly. It takes 1 to 2 weeks for excess-inventory scoring to catch up.
Can Nova track IPI?
Nova tracks the inputs (stranded units, sell-through, days of cover) at the SKU level so you can act before the weekly IPI recalculation.
See this in Nova
Nova surfaces this metric per SKU in near real time so you can act before your next monthly close catches it.
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What is a good sell-through rate on Amazon?
Amazon's sell-through rate is units shipped in the last 90 days divided by average inventory over the same period. Above 3.0 is strong (inventory turns 12x/year). 2.0 to 3.0 is healthy. Below 1.0 usually means overordered units and forecasts long-term storage fees within a quarter.
How do I avoid FBA storage limits?
FBA storage limits are set by IPI score. Keep IPI above 400 by clearing stranded inventory weekly, running removals or liquidations on units aged 180+ days, and keeping your top 20 SKUs consistently in stock. Restock-limited accounts often gain 30% to 60% more capacity within 30 days after a targeted cleanup.
How do I fix stranded Amazon inventory?
Stranded inventory is FBA units that cannot be sold because the listing is suppressed, inactive, or missing key attributes. Fix it in Seller Central under Manage Inventory > Fix Stranded Inventory. Most stranded ASINs resolve within 24 hours after relisting, updating a required attribute, or removing a policy block.
What is days of cover and how do I calculate it?
Days of cover = current on-hand inventory / average daily units sold. If you have 600 units on hand and sell 20/day, you have 30 days of cover. Most sellers target 45 to 75 days of cover for FBA SKUs: enough to survive a demand spike or a shipping delay, not so much that IPI or storage fees suffer.
What triggers Amazon long-term storage fees?
Amazon charges aged inventory surcharges on units stored in a fulfilment centre for more than 181 days. The fee is tiered: 181 to 210 days adds $0.50/cu ft, 211 to 240 days $1.00, 241 to 270 days $1.50, 271 to 330 days $3.90, 331 to 365 days $5.90, and 365+ days $10.90 on top of monthly storage.