Storage is time-dependent. A product can look profitable at receipt and lose that margin when units remain in fulfillment centers, enter a higher-rate period or incur aged-inventory charges.
Formula and decision rule
Allocated storage per sold unit = total storage and age-related charges for the inventory cohort ÷ units ultimately sold from that cohort. For a forward estimate, use unit cubic volume × current monthly rate × expected months held, then add expected age-related charges separately.
Worked example
Suppose a hypothetical unit occupies 0.20 cubic feet, the current rate entered by the seller is $1.00 per cubic foot per month, and average time held is three months. Estimated base storage is $0.20 × $1.00 × 3 = $0.60 per unit before any seasonal or aged-inventory charge.
Why a single annual average fails
Rates and surcharges can change by period, product type and inventory age. Slow inventory also ties up product cost. Keep a base, peak and slow-sell scenario rather than presenting one precise annual estimate.
Inventory review checklist
- Confirm packaged dimensions rather than product-only dimensions.
- Use current Seller Central rates and inventory-age reports.
- Separate base storage from aged-inventory and removal decisions.
- Measure months on hand as average units held ÷ monthly units sold.
Use the calculator
The Amazon FBA Calculator accepts allocated storage directly and reports months on hand and estimated annual inventory turns.
Primary sources
Frequently asked questions
Should aged inventory be averaged across every product?
No. Allocate charges to the affected SKU or cohort when possible; a store-wide average can hide one slow product.
Are storage rates hard-coded in BriskCalc?
No. Sellers enter the current product-specific amount or their own per-unit allocation because rates and product circumstances change.
Change log
Published August 11, 2026 without embedding a rate table that can silently become stale.