IPI (Inventory Performance Index) - Amazon Glossary

Inventory Performance Index (IPI) is a metric used by Amazon to evaluate a seller's overall inventory management efficiency over time. Measured on a scale from 0 to 1000, it assesses how well a merchant balances stock levels, resolves listing issues, and maintains popular products in stock.

Your IPI score directly dictates whether Amazon enforces strict storage volume limits or assesses expensive overage fees on your account. Falling below the platform's required threshold restricts your inbound shipping capacity, which instantly paralyzes your sales velocity and disrupts operational cash flow. Maintaining a high score ensures unlimited storage space or higher baseline limits to protect your quarterly distribution cycles.

What Factors Determine the IPI Score?

Amazon evaluates four core pillars of inventory performance to calculate this aggregate index. Understanding how these factors interact allows brands to maintain high catalog efficiency without absorbing unnecessary logistical costs.

The first pillar is the excess inventory percentage. Amazon flags any SKU that has more than a 90-day supply based on its current sales trajectory. Holding bloated stock levels drags down your index because it signals to the platform that you are utilizing their warehouses as long-term storage facilities rather than fulfillment hubs.

The second pillar is the FBA sell-through rate, which acts as the most critical driver of your score. This metric measures the velocity at which your units move out of the warehouse relative to your average stock levels. A low sell-through rate indicates poor product demand or over-ordering, prompting the algorithm to lower your overall index.

The third component is the stranded inventory percentage. Stranded inventory refers to physical products stored in an Amazon fulfillment center that are completely unbuyable because the associated listing has been deleted, suppressed, or broken by a catalog error. This space-wasting stock harms your score because it occupies warehouse room without any possibility of generating a transaction.

The fourth pillar is the FBA in-stock rate. Amazon monitors whether your top-performing, high-demand products remain available for purchase. If your best-selling variations consistently go out of stock, you lose market share and sales velocity, which negatively impacts your performance index.

How Do You Calculate the FBA Sell-Through Rate?

While the overarching IPI calculation is a multi-factored proprietary algorithm, the primary driver of a healthy score is your rolling sell-through rate. Amazon calculates this metric over a continuous 90-day window to evaluate how efficiently your capital moves through their logistics network.

The mathematical formula for this specific metric is:

$$ \text{FBA Sell-Through Rate} = \frac{\text{Total Units Shipped (Past 90 Days)}}{\text{Average Units in Fulfillment Center (Past 90 Days)}} $$

To execute this calculation accurately, you must monitor your daily shipped orders against the total physical footprint your stock occupies. If this ratio drops below 1.0, it indicates that your inventory is sitting idle, which will negatively pull down your overarching index score.

How Do Fulfillment Models Alter Your IPI Strategy?

The Inventory Performance Index strictly applies to Fulfillment by Amazon (FBA) listings because Amazon wants to optimize space inside its warehouses.

Fulfillment by Amazon (FBA) sellers carry the entire burden of IPI compliance. If your score falls below the target threshold, Amazon applies storage volume limits and hits your account with heavy overage fees for any excess space used.

Fulfillment by Merchant (FBM) sellers do not have an IPI score because they store goods in private facilities. However, FBM serves as a critical hybrid strategy. If an FBA seller's IPI drops and their inbound capacity is throttled, they can instantly pivot their top variations to FBM to maintain sales momentum while liquidating aged inventory from the Amazon network.

Real-World Scenarios in Inventory Management

In Practice: For a 2lb product in the Home & Kitchen category - specifically a set of silicone baking mats - a brand owner monitors their performance weekly. They note their sell-through rate dropping because a specific color variation is moving slowly. To fix this, they run an aggressive 20% off coupon and clean up a brief listing error that caused five units to become stranded. Their IPI score climbs from 420 to 510, safely shielding them from storage volume restrictions ahead of the peak shipping window.

Common Mistake: A competing merchant over-orders 5,000 units of an unverified kitchen gadget to achieve wholesale cost breaks. The item sells only 50 units a month, causing their excess inventory percentage to skyrocket. Concurrently, they ignore their dashboard warnings about three items marked as stranded inventory. Their IPI plunges to 310. Amazon instantly caps their storage capacity, cancels their upcoming inbound shipments, and hits them with a $1,200 monthly storage overage fee that wipes out their entire operational profit.

What Is the SoldScope Expert Tip for Boosting Your IPI?

The most frequent mistake sellers make is trying to fix a low IPI score by aggressively restocking their top-selling items to raise their in-stock rate. This approach backfires because the in-stock rate only tracks whether popular items are available, not how fast they sell; adding more units actually lowers your overall sell-through rate if they don't sell immediately.

Instead, focus entirely on the "Stranded Inventory" and "Excess Inventory" metrics. Fixing stranded listings takes less than five minutes and provides an immediate lift to your score. For slow stock, run aggressive automated multi-buy promotions or flash sales rather than letting them sit. It is far more profitable to liquidate inventory at cost or a slight loss than to pay compounding storage penalties that lock your entire account out of inbound shipments.

How SoldScope Helps

SoldScope replaces manual spreadsheet tracking with automated, data-driven workflows to protect your marketplace efficiency. Sellers utilize the Chrome Extension to conduct real-time inventory level checks and audit competitor stock depths directly on live Amazon pages. Additionally, by executing advanced filtering inside the Product Research tool, brands can accurately project monthly unit velocity and evaluate market demand, ensuring their inbound shipment volumes align precisely with active consumer purchase patterns to prevent margin erosion.