Amazon inventory management is the practice of keeping enough stock available through FBA to meet demand without running out, while avoiding the storage fees, surcharges and capacity limits that punish holding too much. It comes down to knowing your daily sales rate, your full replenishment lead time and your FBA capacity, and reordering against those numbers every week rather than when stock looks low.
We run our own Amazon Professional Seller accounts with Brand Registry, so we plan inbound shipments, fight for capacity and pay these fees with our own money. This guide covers how FBA capacity limits work, what the Inventory Performance Index does today, the storage and inventory level fees, restock math, merchant-fulfilled backup, and what a stockout really costs. Amazon changes these programs and fee schedules regularly, so treat any threshold here as the structure to check against Seller Central, not a fixed number.
How FBA capacity limits work.
FBA capacity limits cap the volume of inventory, measured in cubic feet, that you can have on hand and in transit to Amazon's fulfillment network each month, usually split by storage type such as standard size and oversize. Amazon sets them per account using signals that include your sales history and forecast, how efficiently you use space, and your shipment history. You can see them in Seller Central under the FBA inventory and capacity views, typically with a few months shown ahead.
Amazon also offers a way to request capacity above your limit through a capacity manager, where a request can carry a reservation fee that may be offset by credits as you sell through. Terms change, so read the current rules before relying on it for a peak season.
The practical consequence: capacity, not demand, is often your real ceiling. A brand that sends slow-moving stock uses up the room its best sellers need.
What the Inventory Performance Index does now.
The Inventory Performance Index (IPI) is a score Amazon shows in Seller Central that summarizes how efficiently you manage FBA inventory. Its inputs have been consistent: excess inventory, sell-through rate, stranded inventory (units in a warehouse that cannot be sold because the listing has a problem), and in-stock rate on replenishable items.
What has changed over time is how much the score directly controls. It has historically been tied to storage limits, and Amazon has changed its role in capacity decisions more than once. Our working rule is to treat IPI as a diagnostic, not a target: if the score drops, one of the four inputs moved, and the fix is to that input. Check the current Seller Central help pages for how IPI affects your limits today.
Storage fees, surcharges and the low-inventory fee.
FBA inventory costs come from both directions. The main line items, as structured at the time of writing, are these. Check Amazon's current FBA fee pages for rates, since they are revised regularly.
| Fee | What triggers it | How to manage it |
|---|---|---|
| Monthly storage fee | Every cubic foot of inventory stored, higher in October to December | Keep cover tight on bulky items; plan Q4 inbound by volume, not units |
| Storage utilization surcharge | Stored volume that is high relative to what you ship | Reduce slow movers; balance inbound with sell-through |
| Aged inventory surcharge | Units stored beyond Amazon's age thresholds, roughly six months and up | Watch the aging report monthly; run promotions, remove or liquidate early |
| Low-inventory-level fee | Stock falling below a days-of-supply threshold relative to demand, with exemptions | Keep a steady cover target; ship before you dip, not after |
| Inbound placement fee | How Amazon distributes your inbound shipment across warehouses | Compare placement options when creating shipments |
The low-inventory-level fee is the one that surprises sellers. It exists because Amazon wants a steady flow of stock rather than a trickle, so running lean to avoid storage costs can trigger a per-unit charge on the way out. The answer is a consistent cover target, not a lower one.
“There is no safe place to hide on FBA inventory. Too little costs you a fee and your rank; too much costs you a surcharge and your capacity.”
How to plan restocks.
Amazon's Restock Inventory tool, under Inventory then Inventory Planning in Seller Central, gives recommendations. They are a useful check, but they cannot see your supplier lead time, your minimum order quantities or your cash position. We plan restocks from our own numbers and use the tool to sanity-check.
Peak season needs its own plan. Receiving slows in the weeks before the holidays, storage rates rise from October, and capacity is tight across the network, so Q4 stock usually has to land earlier than your normal lead time suggests. We work backward from the date we want units available, add extra receiving time, and check the stock that is still unsold in January against the aged inventory thresholds before committing the order. Anything that will not sell through by then is cheaper to hold outside FBA.
Some brands add an upstream layer, holding bulk inventory in Amazon Warehousing and Distribution or a third-party warehouse and replenishing FBA in smaller amounts. It makes capacity and storage surcharges easier to manage at the cost of another fee line and more coordination.
Merchant-fulfilled backup and what a stockout costs.
You can list a second offer on the same ASIN under a different SKU, fulfilled by merchant from your own warehouse or a third-party logistics provider. Priced sensibly and with realistic handling time, it sits quietly while FBA stock is available and keeps the listing selling when it is not. It is the cheapest protection against an inbound shipment that arrives late or sits in receiving.
Being in stock is also part of winning the Buy Box against other sellers on your listing, which we cover in how to win the Amazon Buy Box.
What usually goes wrong.
- Averaging sales across stockout days, which understates demand and causes the next stockout.
- Using a supplier's quoted lead time instead of measured lead time including freight and Amazon receiving.
- Sending slow movers into FBA and running out of capacity for the items that actually sell.
- Running lean to cut storage fees and triggering the low-inventory-level fee instead.
- Ignoring stranded inventory, so sellable units sit in a warehouse accruing fees because a listing has an error.
- Leaving aged units until the surcharge applies, when a promotion or removal a month earlier would have cost less.
Where the tools stop and the work begins.
Seller Central shows capacity, IPI, aging and restock suggestions. It does not reconcile supplier lead times, set safety stock for your top sellers, balance capacity across a catalog, keep a merchant-fulfilled backup ready, or coordinate inventory with your advertising calendar. That weekly planning discipline is where inventory stops being a cost center, and it is work Theory Road does as part of our Amazon account management.
What is the Amazon Inventory Performance Index?
The Inventory Performance Index is a score in Seller Central that summarizes how efficiently you manage FBA inventory, based on excess inventory, sell-through rate, stranded inventory and in-stock rate. Its role in capacity decisions has changed over time, so check current Seller Central guidance, and treat a falling score as a signal that one of those four inputs needs attention.
How are FBA capacity limits calculated?
Amazon sets monthly FBA capacity limits per account, in cubic feet and by storage type, using signals such as your sales history and forecast, how efficiently you use space and your shipment history. You can view them in Seller Central and, under current programs, request additional capacity through a capacity manager, which may involve a reservation fee.
What is the Amazon low-inventory-level fee?
It is an FBA fee Amazon applies when a product's available inventory falls below a days-of-supply threshold relative to its demand, with exemptions for some sellers and products. It encourages steady stock levels. The way to avoid it is a consistent cover target and timely reorders, rather than running inventory as lean as possible.
How much inventory should I send to Amazon FBA?
Send enough to cover daily sales across your full replenishment lead time plus a safety buffer, while staying within your capacity limit and below the levels that trigger aged inventory or utilization surcharges. Many sellers plan in days of cover per ASIN and stage shipments rather than sending several months of stock at once.
Should I use FBM as a backup to FBA?
For your best sellers, usually yes. A merchant-fulfilled offer on the same ASIN under a separate SKU keeps the listing buyable when FBA stock runs out or an inbound shipment is delayed. That protects ad delivery and organic rank. It needs reliable fulfillment and accurate handling times so it does not hurt your account metrics.