Amazon rents you warehouse space on its own terms: how much FBA capacity you get is granted monthly based on how well your inventory performs, shown ahead in Seller Central’s capacity monitor, and priced punitively when stock overstays. Sellers who treat FBA as their warehouse fight the limits forever; sellers who treat it as a fast-moving forward position, fed from their own storage on data, mostly stop noticing limits exist.
How the capacity system works
Seller Central’s capacity monitor shows your limit per storage type for the current period and estimates for coming months, so inbound planning has a horizon. The grant tracks two things: your sales forecast on Amazon and your Inventory Performance Index (IPI), the score summarizing how efficiently you use the space. Need more than granted? Amazon’s capacity manager lets you request additional space with a reservation fee that performance credits offset when the extra space earns sales, space you can bid for, priced so that only stock that sells is worth bidding on.
IPI’s drivers are public and operational: excess inventory percentage (months of supply beyond need), FBA sell-through, stranded inventory percentage (stock unsellable from listing problems), and in-stock rate on your movers. Notice what that list is: turnover discipline, dead-stock hygiene, listing health, and replenishment timing, Amazon scored what good practice already looks like.
The fee stack enforces it: monthly storage fees that jump for Q4, aged-inventory surcharges once units sit past thresholds (the half-year mark is where it bites), overage fees for exceeding capacity, and a low-inventory-level fee on the other edge for popular SKUs kept too thin against their demand. The message from both directions: match FBA stock to near-term demand, neither hoard nor starve.
The strategy: FBA as forward position
- Send weeks, not quarters. FBA holds four to eight weeks of cover for proven movers, the cover math per SKU, while depth lives in your own or third-party storage where space is cheaper and unscored, the FBA-versus-FBM split applied to the same SKU.
- Replenish on data, not on truck schedules. Send-less-more-often only works with live velocity per SKU and alerts before the low-inventory edge, exactly what a synced inventory pool computes continuously across your channels.
- Let losers leave. Removal orders and clearance before the aged surcharge beat paying rent on regret; the IPI excess metric improves as a side effect.
- Fix stranded stock weekly. Units in the warehouse with no active listing score against you while earning nothing, a five-minute Seller Central check.
- Plan Q4 early: the holiday buy meets peak storage pricing and capacity demand at once, inbound staged in waves beats one September wall of pallets.
Common questions
My capacity limit is tiny as a new FBA seller - normal?
Normal: no history means a small grant. Send a modest, fast-selling assortment, sell through cleanly, and the forecast-driven grant grows with the sales.
Does multichannel stock help or hurt here?
Helps, structurally: your own pool serves every channel while FBA holds just Amazon’s near-term need, and multichannel fulfillment can even ship other channels’ orders from FBA when the economics fit.
What single number should I watch?
Sell-through against your capacity: FBA units sold over average units held. It drives IPI, storage cost per sale, and the next month’s grant all at once.
Is bidding for extra capacity ever right?
For a proven seasonal surge with margin behind it, yes, the performance credits offset the fee when the stock sells. As a chronic workaround for slow inventory, never; the fee is Amazon telling you the stock should not come.
The forward position, fed on data
Low-stock alerts across every channel from $49/month with unlimited orders, and the per-SKU velocity and days-of-cover replenishment engine that keeps FBA lean and never empty on the plans above. See pricing.