An Amazon storage fee calculator is a spreadsheet with one row per SKU and four numbers per row: cubic feet per unit, average units on hand, the storage rate for the month, and the units that have crossed the aged-inventory line. Multiply across, add the aged surcharge, and read the total against what the SKU earns. Amazon charges monthly storage on the daily average cubic feet your inventory occupies, with higher rates in the holiday months, and it adds an aged-inventory surcharge on units stored more than 181 days (sell.amazon.com FBA page and FBA fees guide, July 2026). Both charges are per SKU in effect even when Amazon bills them in total, and a per-SKU model is the only way to see which products are paying rent they cannot afford.
Amazon's public seller pages describe the structure: monthly storage by cubic foot, seasonal rates with the holiday months higher, an aged surcharge tiered by how long units have sat. Amazon does not hold the rates still. The 2026 schedule is covered in Amazon FBA fees 2026, and the live figures sit in Seller Central. This article uses clearly illustrative rates so the arithmetic is reproducible; swap in the current schedule before you decide anything with it.
Build the sheet with these columns, left to right.
The formulas, in spreadsheet terms: cubic feet per unit is `=L*W*H/1728`; total cubic feet is `=units*cuft`; monthly storage is `=IF(month>=10, peak_rate, offpeak_rate)*total_cuft`; aged surcharge is `=aged_units*cuft*aged_rate`; the share is `=(storage+aged)/contribution`.
Illustrative numbers, including the rates. Off-peak storage at $0.80 per cubic foot, peak at $2.40, aged surcharge at $1.50 per cubic foot on units past 181 days. These are placeholders chosen to make the arithmetic clear; they are not Amazon's rates.
SKU-P, foam yoga block. Packaged 4 by 6 by 9 inches. 216 cubic inches divided by 1,728 equals 0.125 cubic feet per unit. Average 2,400 units on hand, so 300 cubic feet. Off-peak storage: 300 times $0.80 equals $240.00. Peak: 300 times $2.40 equals $720.00. Aged units: 900, or 112.5 cubic feet, times $1.50 equals $168.75. Contribution before storage: $3,100.
SKU-Q, phone stand. Packaged 3 by 3 by 4 inches. 36 cubic inches, or 0.0208 cubic feet. Average 5,000 units, 104.2 cubic feet. Off-peak $83.33. Peak $250.00. No aged units. Contribution before storage: $6,400.
SKU-R, folding step stool. Packaged 14 by 12 by 2.5 inches. 420 cubic inches, or 0.2431 cubic feet. Average 800 units, 194.4 cubic feet. Off-peak $155.56. Peak $466.67. Aged units: 500, or 121.5 cubic feet, times $1.50 equals $182.29. Contribution before storage: $900.
Now the last column, which is the reason the sheet exists.
September, off-peak. SKU-P pays $240.00 plus $168.75, or $408.75, against $3,100 of contribution: 13.2 percent. SKU-Q pays $83.33 against $6,400: 1.3 percent. SKU-R pays $155.56 plus $182.29, or $337.85, against $900: 37.5 percent. Catalog total $829.93 against $10,400, or 8.0 percent.
October onward, peak. SKU-P: $720.00 plus $168.75 equals $888.75, or 28.7 percent of contribution. SKU-Q: $250.00, or 3.9 percent. SKU-R: $466.67 plus $182.29 equals $648.96, or 72.1 percent of contribution. Catalog total $1,787.71 against $10,400, or 17.2 percent.
The catalog figure looks tolerable in both seasons. The SKU figures do not. SKU-R hands Amazon nearly three quarters of what it earns during peak, and the aged surcharge alone is a fifth of its contribution before the seasonal rate even applies. SKU-Q could sit in Amazon's warehouse all year and nobody would notice. SKU-P is the one to watch: fine today, and 900 aged units that will not clear before the peak rate arrives.
That is what a blended storage line on the P&L hides. $1,787.71 of "FBA storage fees" in October is a number. $648.96 of it on a product earning $900 is a decision.
The sheet is only as good as three inputs, and none of them come from Amazon.
Contribution before storage. Price minus referral fee, fulfillment fee, ad spend, refunds, and FIFO landed COGS, by SKU, for the month. If you do not have this, the last column is blank and the sheet is a fee estimate with no way to judge it. Inventory reporting that carries value and aging by SKU, joined to SKU-level profit, is the source.
Aged units by SKU. Amazon's inventory age report gives its view. Your own receiving dates give another, and they differ when stock sat at a 3PL before going inbound. Use Amazon's for the surcharge (Amazon bills on its own clock) and yours for the write-down question.
Average units, not month-end units. A SKU that received 3,000 units on the 28th shows a large month-end balance and a small average. Amazon bills on the average.
Once SKU-R shows 72.1 percent, the question changes from "what does storage cost" to "what do I do with 500 aged step stools before October." Four paths: hold and pay, discount to clear, create a removal order, or liquidate. The arithmetic for each is in Amazon Q4 storage fees: keep, discount, liquidate, or remove. The short version: the $9.60 you paid per stool is gone either way, so compare the cash each path returns from here, net of the storage each path incurs between now and the sale.
The three-SKU sheet takes twenty minutes. The 300-SKU version takes a day and goes stale the week after you build it. Crunch, the analytics AI inside ConnectBooks, answers "should I liquidate, remove, or hold this inventory ahead of Q4 storage fees" from your reconciled data: it treats paid COGS as sunk and weighs future storage fees, long-term and aged-inventory fees, expected sell-through, selling fees, sales velocity, expected cash recovery, and incremental cash contribution, then ranks each SKU as hold, discount, liquidate, or remove. It reads the rates and the aging as they stand in your data. It does not know a promotion you are planning, it cannot see a PO that has not been entered, and it does not file the removal order. You do.
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