FBA Storage Fees: How the Math Actually Works

Two separate charges, often mistaken for one

Amazon bills FBA sellers for storage in two different line items, and most sellers only ever look at one of them. The monthly storage fee is charged on every unit sitting in a fulfillment center, based on the space it occupies, its size tier (standard or oversize), and the month — peak months cost noticeably more than off-peak ones. The aged inventory surcharge is a second, separate charge that only kicks in once units have been sitting for a while, and it stacks on top of the monthly fee rather than replacing it.

Neither of these is the same as a fulfillment fee (what you pay to pick, pack, and ship an order) or a referral fee (Amazon's commission on the sale). Storage fees are charged whether or not the unit ever sells. You'll find both in Seller Central under Reports → Fulfillment → Storage Fees, and you can estimate upcoming charges in the Fee Preview report before you even ship a shipment in.

How the monthly storage fee is actually calculated

The formula is simple once you see it: average daily volume in cubic feet, multiplied by the rate for your size tier and month. Cubic feet per unit is length × width × height in inches, divided by 1,728.

Say a product ships in a box 12 × 10 × 8 inches. That's 960 cubic inches, or 0.556 cubic feet per unit. Hold 500 units at that average volume for a month and you've got roughly 278 cubic feet of occupied space. To show the mechanics — not to quote Amazon's current rate, which changes by size tier and season and which you should pull from your own Fee Preview report — use $1.00 per cubic foot as a stand-in for an off-peak month. That's $278. Swap in a peak-month rate of $2.50 for the same 278 cubic feet and the bill jumps to $695, for the exact same inventory. Nothing about the product changed. Only the calendar did. That's the single biggest lever most sellers ignore: timing inbound shipments so peak-season volume isn't sitting in FBA any longer than it has to be.

The aged inventory surcharge is a second, separate bill

Once units have been in a fulfillment center past a certain age, Amazon adds a surcharge on top of the regular monthly fee. It's structured in bands — units sitting for roughly six months carry a lower surcharge than units sitting for nine months, which carry less than units past a year — and the exact day cutoffs and per-unit rates move, so check your current Storage Fees report rather than trusting a number from memory or a blog post.

The design intent is straightforward: Amazon wants the surcharge to make holding dead stock cost more than moving it, whether that's through a price drop, a removal order, or liquidation. The mistake we see most often is sellers treating the aged surcharge as a cost of doing business instead of a signal that a SKU needs a decision.

The mistakes that inflate this line item most

Across the more than $500M in managed revenue Full Circle has managed for 100+ brands, the single most repeated storage-fee mistake is dimensional drift: a packaging change — a thicker mailer, a new retail box, a bundled multipack — quietly pushes a product from the standard size tier into oversize, and nobody updates the listing or checks the fee report for three months. The rate difference between tiers is large enough that this alone can double a SKU's monthly storage line without a single unit of extra stock being held.

• Not reconciling Fee Preview against actual charges — the estimate and the bill can diverge when dimensions on file are stale.
• Letting the removal-versus-liquidation decision drift — the surcharge keeps climbing while someone decides.
• Inbounding peak-season volume too early — the units sit through a full high-rate month before they even go on sale.
• Treating storage fees and the aged surcharge as one number — they need separate fixes.

What to do when the number is wrong, or the fix isn't working

Start by comparing the Storage Fees report against Fee Preview for the same SKU and month. If they don't match, the most common cause is dimensions or weight on file that no longer reflect the physical product — measure a live unit yourself and file a correction if it's off. If the tier and rate are correct and the charge still looks high, the fix usually isn't a dispute, it's a decision: work out whether continued storage plus a climbing surcharge costs more than a removal order, and whether removal costs more than liquidation recovery, on that specific SKU, this month — not the SKU's history, its current trajectory.

If the fee is genuinely wrong — charged at the wrong tier, wrong month, or for units you no longer hold — that's a case to open with Seller Support, with the report data attached. It won't get waived on request; it gets corrected when the evidence is clear.