Two inventory problems will silently kill your Amazon business. One is obvious. One isn’t.
The obvious one is stockouts. You run out of inventory, your listing disappears from search results, and you lose rank that took months to build. Every day you’re out of stock, a competitor takes your position — and they don’t give it back when you restock.
The less obvious one is overstock. Excess inventory sitting in FBA warehouses costs you money every month in storage fees, eventually triggers long-term storage fees that run $6.90 per cubic foot, and can trigger automatic price reductions that crater your margins.
Most brands manage inventory reactively — they restock when they run out and panic-ship when fees spike. The brands that scale manage inventory proactively, with systems. Here’s how to build one.
Why Inventory Management Is a Ranking Problem, Not Just a Cash Flow Problem
Most sellers think of inventory as a finance issue. It isn’t. It’s an algorithm issue.
Amazon’s A9 algorithm uses sales velocity as one of its core ranking signals. When your product is in stock and selling consistently, the algorithm rewards you with organic visibility. When you go out of stock, the algorithm interprets it as demand dropping — and it moves other products into your position.
The math is brutal: if you rank #3 for your main keyword and go out of stock for 10 days, you might come back to find yourself at #15 or lower. Getting back to #3 requires rebuilding the sales velocity that earned that position in the first place — often another 30–60 days of PPC spend and discounting.
A single stockout on a high-velocity ASIN can cost more in lost revenue and recovery spend than an entire year of proper inventory planning would have cost. This is not theoretical — we see it happen to brands we onboard regularly.
The Core Metrics You Need to Track
Before you can manage inventory well, you need to know your numbers. These are the metrics that matter:
Days of Supply (DoS): how many days of inventory you have left at your current sell rate. Formula: units in FBA divided by average daily sales. If you have 200 units and sell 10 per day, you have 20 days of supply.
Sell-Through Rate: units sold in the last 90 days divided by average units in FBA over that period. Amazon uses this to calculate your IPI score and determine your storage limits. Below 2.0 is a red flag.
Lead Time: how long it takes from placing a purchase order to having inventory available in FBA. This includes manufacturing time, freight, customs, and Amazon’s receiving window. For most China-sourced products, total lead time runs 45–90 days.
Reorder Point: the inventory level at which you need to place a new purchase order to avoid a stockout. Formula: (average daily sales x lead time in days) + safety stock.
Safety Stock: extra inventory buffer to absorb demand spikes, supplier delays, or freight disruptions. A common formula: average daily sales x (maximum lead time minus average lead time).
If you don’t know these numbers off the top of your head for your top 5 ASINs, your inventory management is reactive.
How to Calculate Your Reorder Point
This is the most important calculation in FBA inventory management — and most sellers don’t do it.
Here’s a worked example:
- Average daily sales: 15 units
- Average lead time: 60 days
- Maximum lead time (supplier delay scenario): 75 days
- Safety stock: 15 x (75 – 60) = 225 units
- Reorder point: (15 x 60) + 225 = 1,125 units
When your FBA inventory drops to 1,125 units, you place a new purchase order. Not when you hit 200 units. Not when you get an Amazon low-inventory warning. When you hit 1,125.
Run this calculation for every ASIN. Set calendar reminders or use inventory management software to alert you when you hit your reorder point.
The Overstock Problem: Storage Fees and IPI
Overstock is the other side of the problem — and it’s more common than stockouts among brands that have been on Amazon for more than a year.
Amazon’s Inventory Performance Index (IPI) is a score between 0 and 1,000 that measures how efficiently you’re using FBA storage. If your IPI drops below 400, Amazon limits your storage capacity. If you’re a high-volume seller in Q4, a storage limit is catastrophic.
The main drivers of low IPI:
- Excess inventory: units that have more than 90 days of supply on hand
- Low sell-through rate: product that isn’t moving relative to how much storage it’s occupying
- Stranded inventory: listings that are inactive but still have units in FBA
- Unfulfillable inventory: damaged or unsellable units sitting in the warehouse
Long-term storage fees hit hard. Any inventory that has been in FBA for more than 365 days gets charged $6.90 per cubic foot per month. For bulky products, that adds up to hundreds of dollars per month for inventory you should have liquidated months ago.
Practical Strategies to Prevent Overstock
Use Sales Rank and Velocity Data to Forecast Accurately
Don’t forecast based on last month’s sales alone. Look at 90-day trends. If your sell-through rate is declining, your reorder quantity should decline with it. If you’re entering a seasonal peak (Q4, Mother’s Day, Prime Day), model the spike into your projections.
Create Removal Orders for Slow-Moving Inventory
If an ASIN has more than 180 days of supply and isn’t trending toward selling down, create a removal order. Removal costs $0.97–$2.00 per unit. Long-term storage fees will exceed that within a month on most products. Take the small loss now to avoid the larger ongoing cost.
Use FBA Liquidations for Unsellable Overstock
Amazon’s liquidation program lets you sell excess inventory to liquidators at a fraction of retail (typically 5–15 cents on the dollar). It’s not a good outcome — but it’s better than paying $6.90 per cubic foot per month indefinitely.
Run Strategic Promotions to Accelerate Sell-Through
If you’re approaching the 90-day or 365-day thresholds, use coupons, Lightning Deals, or price reductions to move inventory before fees hit. A 20% discount to clear inventory is always better than months of storage fees plus the eventual liquidation cost.
Tools That Actually Help
- Inventory Planner: syncs with Seller Central and generates reorder recommendations based on sales velocity and lead times. The most widely used dedicated inventory tool among 7-figure Amazon brands.
- Helium 10 Inventory Management: part of the Helium 10 suite. Works well for sellers already using Helium 10 for keyword research.
- Skubana / Extensiv: enterprise-level inventory and order management. Better suited for brands selling across multiple channels.
- Amazon’s own restock recommendations: available in Seller Central under Inventory > Restock Inventory. Useful as a secondary data point, but often conservative and doesn’t account for your specific lead times.
For most brands doing $500K–$3M annually on Amazon, Inventory Planner is the right tool. It pays for itself within a month of avoiding a single stockout.
What Good Inventory Management Actually Looks Like
The brands we work with at Bullseye Sellers that manage inventory well share a few common practices:
- They check Days of Supply on their top 10 ASINs every Monday
- They have reorder points set in their inventory software and act on alerts the same day they trigger
- They review their IPI score weekly and address any “excess inventory” flags before they impact their score
- They build lead time variability into every purchase order — they never assume best-case supplier timelines
- They treat Q4 as a separate planning exercise starting in July, because demand spikes require inventory decisions made 90+ days in advance
None of this is complicated. It’s discipline applied consistently.
The Cost of Not Managing Inventory
We’ve onboarded brands that lost their page-one ranking for primary keywords during a stockout and spent $15,000–$30,000 in PPC over the following quarter rebuilding it. We’ve seen brands pay $40,000+ in a single year in long-term storage fees on slow-moving SKUs they should have liquidated at Q2.
These are real, preventable losses. They happen to smart, successful sellers who are focused on marketing and product development — and not watching the operational details that quietly drain profitability.
If you want help building a proper FBA inventory system — or if you’re already dealing with a stockout or overstock situation that needs fixing — book a strategy call with Bullseye Sellers. We’ll audit your current inventory position and tell you exactly what needs to change.
