Inventory Performance Index Explained: How Amazon’s IPI Score Controls Your FBA Storage
TL;DR
Your Inventory Performance Index is Amazon's 0 to 1,000 score for how efficiently you run FBA inventory. It blends excess inventory, sell-through rate, stranded inventory, and in-stock rate. Stay above 400 and you keep unrestricted storage. Drop below and Amazon caps your capacity, usually right before peak season.
You find out your storage got cut the same week you place a 5,000 unit reorder. That is the Inventory Performance Index doing its job, quietly, in the background, until it is suddenly your problem. Most sellers never look at the score until Amazon uses it against them. By then the cut is already locked in for the quarter.
So let us fix that. This guide breaks down what the score actually measures, how Amazon weights each piece, what the 400 line really triggers, and the exact moves that lift it fast. No fluff, just the mechanics and the math.
Jump to the section you need:
What Is the Inventory Performance Index?
The Inventory Performance Index is the score Amazon uses to decide how much storage your account gets in FBA fulfillment centers. It rolls four behaviors into one number that updates weekly, on a scale from 0 to 1,000.
Definition
The Inventory Performance Index (IPI) is Amazon's 0 to 1,000 efficiency score for FBA inventory. It weighs excess inventory, sell-through rate, stranded inventory, and in-stock rate. Sellers above the threshold keep unrestricted standard storage. Sellers below it get capacity restrictions.
You find your score in Seller Central under Inventory, then FBA Inventory, then Inventory Performance. Think of it less as a vanity metric and more as a credit score for warehouse space. A high number buys you room to stock aggressively before Q4. A low number boxes you in at the worst possible time.
Here is the part most guides skip. Amazon does not publish the exact formula. It describes the four inputs qualitatively, so the weights you see online are estimates from seller testing, not Amazon math. That matters, because it means you manage the inputs, not the output. Fix the behaviors and the number follows.
How Amazon Calculates Your IPI Score
Amazon builds your IPI score from four inputs, measured on a rolling 90-day window. Two of them carry most of the weight. Get those two right and the rest follows.
| Component | Estimated weight | What it measures | Target |
|---|---|---|---|
| Excess inventory % | 40 to 45% | Units beyond ~90 days of forward supply | Below 5% |
| Sell-through rate | 30 to 35% | Units shipped vs. average units on hand (90 days) | Higher is better |
| Stranded inventory % | 15 to 20% | FBA units with no buyable listing | 0% |
| In-stock rate | 10 to 15% | Top replenishable ASINs in stock over 30 days | Above 90% |
Excess inventory and sell-through rate together drive roughly 70 to 80% of the score. So if you only have time to fix two things this week, fix those two.
The other two matter at the edges, but they bite fast when they break. A few stranded units can knock 30-plus points off in a single weekly refresh. In-stock rate is the quiet one: let your best ASINs run dry and the score slips even while your warehouse looks clean.
What Happens When Your IPI Drops Below 400?
When your IPI drops below 400, Amazon caps your standard-size storage capacity and can tighten your restock limits for the upcoming quarter. The threshold sits at 400 as of 2026, down from 450 in 2025, though Amazon can move it quarterly based on network capacity.
The cap itself is not the real damage. The trap is the loop it creates. Less storage means you cannot send in enough fast movers. Thin fast-mover stock hurts sell-through. Weak sell-through drags the score down further. Now you are stuck under the line, bleeding sales you cannot see.
Here is the math on what that costs. One seller I talked through this had an IPI of 430 and was burning capacity on 150 slow SKUs while their top 5 ASINs ran thin. The stockouts on those 5 products cost an estimated $4,200 per month in lost sales. The slow stuff was not just dead weight, it was actively starving the winners.
The flip side is just as real. Moving a score from 430 to 540 by clearing excess and unstranding listings added roughly 18% more storage capacity heading into Q4. That is the difference between stocking for peak season and watching competitors take the sales while you wait on a restock window.
Want IPI fixes in your inbox?
Get one practical Amazon FBA inventory breakdown a month, written for operators. No fluff, unsubscribe anytime.
How to Improve Your Inventory Performance Index
To improve your Inventory Performance Index, attack the two heaviest inputs first: clear excess inventory and lift sell-through. Everything else is cleanup around those two. Here is the order I run it in, fastest payoff first.
- Fix stranded listings today. This is the single fastest lever. Most stranded units relist or remove within hours, and because the score refreshes weekly, a Monday fix shows up by the next Monday.
- Liquidate or remove aged excess. Sort your excess inventory report by estimated cost. Anything past 90 days with fewer than 5 units sold in 30 days gets a removal order, a price cut, or an outbound deal.
- Pull excess off Amazon, do not just discount it. Move slow stock to AWD or a 3PL so it stops counting against your excess percentage while you sell it down.
- Tighten reorder timing on your winners. Keep your top ASINs in stock without overshooting. A clean inventory turnover rhythm protects both sell-through and in-stock rate.
- Audit weekly, not quarterly. The score moves on a 90-day rolling window, so small weekly corrections compound. Waiting for the quarterly evaluation is how sellers get surprised.
| Lever | Speed to impact | Effort |
|---|---|---|
| Unstrand listings | 1 week | Low |
| Remove aged excess | 1 to 2 weeks | Medium |
| Shift stock to AWD/3PL | 2 to 4 weeks | Medium |
| Reorder timing discipline | Ongoing | Ongoing |
One more thing sellers underrate: a score of 420 is not safe, it is barely safe. That 20-point cushion above 400 can evaporate in a single quarter if excess creeps up or a batch of listings gets suppressed. Build for 500-plus and treat anything under 450 as a yellow light.
Common IPI Mistakes That Quietly Tank Your Score
Most IPI damage is self-inflicted and avoidable. The same handful of mistakes show up across accounts, and each one has a clear consequence.
- Treating excess as a storage-fee problem. The fee is the smallest cost. The real bleed is trapped capital and the IPI drag. See our breakdown of FBA excess inventory for the full cost math.
- Ignoring stranded units. They cost storage, generate zero sales, and hit the stranded component hard. A suppressed listing left for a week is points off your score for nothing.
- Letting inventory age past the surcharge cliffs. The jump from the 271-day to the older tiers can be a 990% fee increase overnight. Track age at the SKU level, not the account level. Our aged inventory surcharge guide has the tiers.
- Overstocking slow SKUs to chase in-stock rate. You protect one small component and blow up the heaviest one (excess). Net result: lower score.
- Reacting at the quarterly check instead of weekly. By the time the formal evaluation hits, roughly six weeks before quarter end, the damage is already in the 90-day window.
If you want the source of truth on thresholds and reports, Amazon documents the score and where to find it in Seller Central. Always confirm the current threshold there, since Amazon adjusts it quarterly.
Inventory Performance Index FAQ
What is a good IPI score on Amazon?
A good IPI score is anything comfortably above the 400 threshold, and 500 or higher gives you real headroom. Above 400 you keep unrestricted standard-size storage. Between 400 and 450 you are technically safe but exposed, since one quarter of excess inventory can push you under.
How is the Amazon IPI score calculated?
Amazon calculates IPI from four inputs on a rolling 90-day window: excess inventory percentage, sell-through rate, stranded inventory percentage, and in-stock rate. Excess inventory and sell-through carry the most weight, together driving roughly 70 to 80% of the score. Amazon does not publish the exact formula or weights.
What happens if my IPI drops below 400?
If your IPI drops below 400, Amazon caps your standard-size storage capacity and can tighten your restock limits for the next quarter. That usually means you cannot send in enough fast-moving inventory, which hurts sell-through and makes the score harder to claw back.
How often does Amazon update your IPI score?
Amazon updates your IPI score weekly, usually on Monday or Tuesday, on a rolling 90-day window. Formal quarterly evaluations about six weeks before each quarter ends decide whether you face storage limits in the coming quarter.
The Bottom Line
Your Inventory Performance Index is not a dashboard vanity metric. It is the gate between you and the warehouse space your business runs on. Watch the two heavy inputs, fix stranded stock the day it appears, and never let a 420 fool you into thinking you are safe. Manage the inputs weekly and the score takes care of itself, right when you need the capacity most.
