FBA storage fees: the complete breakdown
Amazon charges you to store your inventory in their fulfillment network. These fees are unavoidable when using FBA, but understanding them helps you make smarter decisions about what to send in, how much to send, and when to remove slow-moving stock.
Monthly storage fees
Amazon charges monthly storage fees per cubic foot of space your inventory occupies. The rates vary by time of year: January through September is the standard rate, while October through December (the holiday season) is higher, sometimes significantly. The exact rates change annually, so always verify current rates in Seller Central under FBA > FBA Inventory > Storage.
Standard-size products are charged at a lower per-cubic-foot rate than oversize products. The size tier your product falls into affects not just storage fees but all FBA fees, so knowing your product's size tier is fundamental to understanding your FBA cost structure.
Aged inventory surcharge (formerly long-term storage fees)
Amazon charges an additional surcharge for inventory that has been in their warehouses for extended periods. The fee structure applies in tiers: inventory aged 181-270 days incurs one rate, 271-365 days a higher rate, and 365+ days the highest rate. These fees are assessed monthly based on the inventory snapshot taken around the 15th of each month.
The aged inventory surcharge can quickly exceed the value of the product for slow movers. A $5 item that's been in FBA for 13 months could be costing you more per month in storage than it's worth. Regular inventory audits with an eye on age are essential to catching these situations before they compound.
The removal math
Amazon offers two options for inventory you want out of their warehouses: removal orders (they ship it back to you) and disposal orders (they throw it away). Both have per-unit fees. For most sellers, the math is: if the removal cost plus shipping back to your warehouse is less than the expected future aged inventory fees, remove the product. If it's genuinely worthless, dispose it.
Run this math on any product approaching the 181-day threshold that isn't moving. Letting aged stock sit is one of the most common FBA profit leaks.
Restock limits and how to manage them
Amazon imposes restock limits that cap how much inventory you can have in their network at any given time. These limits are account-wide across all your ASINs in a given storage type (standard size, oversize, apparel, footwear, etc.).
How restock limits are calculated
Amazon calculates your restock limits based on your IPI score (covered in the next section) and your recent sales velocity. Sellers with higher IPI scores and strong sell-through rates get higher limits. Sellers with low scores or lots of aged, slow-moving inventory get tighter limits.
Restock limits reset periodically (Amazon communicates the dates in Seller Central). Between resets, your limit is fixed regardless of how much you sell. This means a strong sales month doesn't immediately unlock more capacity; you have to wait for the next limit calculation cycle.
Strategies for constrained limits
When your restock limit is binding (you can't send in as much as you want), you have two levers: reduce the inventory you have in the network (remove slow movers to free up capacity for fast movers) or work within the constraint by prioritizing which ASINs get FBA allocation.
Many constrained sellers use a hybrid FBA/FBM strategy: FBA for their fastest-moving SKUs where Prime matters most for conversion, and FBM for slower movers or products where Prime isn't a decisive factor. This lets you allocate your limited FBA capacity to where it creates the most value.
Review your FBA inventory age report in Seller Central at least monthly. Sort by days in warehouse descending. Any product over 120 days with low velocity is a candidate for a promotional push, a price reduction to accelerate sell-through, or a removal order. Don't wait until 181 days to act; the aged surcharge tiers up sharply and you have less time to respond.
Stranded inventory: causes and fixes
Stranded inventory is FBA inventory that Amazon has in its warehouse but that isn't connected to an active listing. Amazon cannot sell stranded inventory, so you're paying storage fees for units that generate no revenue. Stranded inventory is often invisible to sellers who don't actively monitor it.
Common causes of stranded inventory
The most common cause is a listing going inactive. This can happen for many reasons: a listing violation (Amazon removed it), a pricing error triggering Amazon's fair pricing policy, an expired listing that wasn't renewed, a change in category requirements, or an account health issue that caused Amazon to suppress listings.
Another common cause is a mismatch between the FNSKU (the barcode on your FBA units) and the current active ASIN. This can happen after product relisting, ASIN merges, or variations being reorganized. Amazon's warehouses have your units under one code, but the listing uses a different code.
Finding and fixing stranded inventory
In Seller Central, go to Inventory > FBA Inventory and look for the "Stranded Inventory" tab or filter. Amazon shows you each stranded unit, the reason it's stranded, and recommended actions. Common fixes: relist the item (if the listing was closed), fix the pricing issue (if it was suppressed for pricing), or create a removal order (if the cause isn't fixable).
Set up a weekly review of your stranded inventory. A unit stranded for 30 days has already cost you 30 days of storage fees for no revenue. Units stranded for 181+ days hit aged inventory surcharges. Address stranded inventory promptly.
Understanding your IPI score
The Inventory Performance Index (IPI) is Amazon's score of how efficiently you're using your FBA storage. It ranges from 0 to 1,000. Amazon requires sellers to maintain an IPI above a minimum threshold (currently 400, but verify current requirements in Seller Central as this can change). Sellers below the threshold face reduced restock limits.
What goes into your IPI score
Amazon doesn't publish the exact formula, but IPI is primarily influenced by four factors: excess inventory percentage (how much of your inventory is considered excess relative to demand), stranded inventory rate (units stuck without an active listing), FBA sell-through rate (units sold in the last 90 days divided by average inventory), and in-stock rate for your top-performing ASINs.
How to improve your IPI score
The most direct improvements: clear stranded inventory (it's a direct deduction from your score), remove or liquidate excess slow-moving inventory (reduces excess inventory percentage), and run promotions on slow sellers to improve sell-through rate. If you have ASINs that are frequently out of stock on your top sellers, improving restock timing improves your in-stock rate component.
Don't chase IPI as a goal in itself. Chase the underlying behaviors: accurate inventory levels, active listings, reasonable sell-through velocity. The score follows the behavior.
FBA inventory planning that actually works
FBA inventory planning requires balancing two competing risks: send too much and pay aged inventory fees; send too little and stock out, losing ranking and sales. Most sellers err toward one side or the other based on their personality, when the math says the right answer varies by product.
The coverage model
A simple and practical model: for each ASIN, calculate daily sales velocity (total units sold in last 30 days / 30). Multiply by your desired coverage (say, 45 days' worth). Add your safety buffer (typically 15-20% to account for velocity spikes). The result is your target FBA quantity. Your restock trigger is when current FBA inventory falls below your lead time days multiplied by daily velocity.
Coverage = (daily velocity x 45) + (daily velocity x 45 x 0.15)
This formula isn't perfect, but it's repeatable, which means you can review and improve it over time. Ad-hoc gut-feel reorder decisions are harder to learn from.
Seasonal adjustments
FBA inventory planning in Q3 (preparing for Q4) is its own exercise. Lead time from your supplier to your warehouse to FBA check-in can be 6-10 weeks if you're sourcing overseas. That means you need to be ordering Q4 inventory in August or September at the latest. Sellers who don't plan for this run out of stock in November, exactly when Amazon's traffic is highest and sales would be strongest.
The restock report in Seller Central
Seller Central's Restock Inventory report generates suggested restock quantities per ASIN based on your sales velocity and your specified lead times. It's not perfect, but it's a useful starting point. Set your lead times accurately (supplier lead time + transit to your warehouse + prep time + FBA check-in time) and the recommendations become more useful.
FBA and multichannel inventory sync
If you're selling on Shopify, Etsy, or other channels in addition to Amazon, FBA introduces a specific inventory challenge: the inventory in Amazon's warehouses is physically separate from the inventory in your own warehouse or 3PL. You need to track both pools and ensure that sales from any channel reduce the right pool.
Multi-channel fulfillment (MCF)
Amazon offers Multi-Channel Fulfillment (MCF), which lets you use Amazon's FBA warehouses to fulfill orders from your non-Amazon channels (Shopify, your own website, etc.). When a Shopify order comes in, MCF can pick, pack, and ship from your Amazon FBA stock.
MCF fees are higher than standard FBA fulfillment fees, and orders show up in Amazon-branded packaging (which can dilute your brand on Shopify orders). For some sellers it's worth it for the simplicity; for others, the branding issue is a dealbreaker.
Separate pools: FBA + own warehouse
The more common model is keeping FBA inventory separate from your Shopify/direct channel inventory. FBA stock fulfills Amazon orders. Your own warehouse stock fulfills everything else. Commerce Kitty handles this by syncing the non-FBA channels against your warehouse stock, while Amazon FBA manages its own pool independently. See how to set this up in our guide on FBA inventory sync setup and on Shopify and Amazon inventory sync.
Preventing FBA stockouts from affecting other channels
If FBA goes out of stock, your Amazon listing may go dark (or lose the Buy Box). This doesn't directly affect your Shopify inventory since they're separate pools. But if you're running FBM as a backup for Amazon, you need your FBM inventory (typically your own warehouse) to also be synced with Shopify and other channels. Otherwise a large batch of FBM Amazon orders could deplete stock that other channels thought was available. See our guide on preventing Amazon FBA overselling for the full picture.
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