Start with a real per-unit P&L
Most sellers know their referral fee and their fulfillment fee. Far fewer subtract storage, inbound transport, placement, returns processing, removals, and advertising spend allocated per unit sold. The result is a catalog where a third of the SKUs look profitable in a spreadsheet and lose money in reality.
Build one row per ASIN with landed product cost, referral fee, fulfillment fee, monthly storage, aged inventory surcharge, inbound and placement cost, returns rate multiplied by returns processing, and advertising cost per unit. What is left is contribution margin. Anything under your floor gets repriced, repackaged, bundled, or removed.
| Cost line | Where it hides | Lever |
|---|---|---|
| Fulfillment fee | Size tier and unit weight | Repackage to drop a tier |
| Storage and aged surcharge | Slow SKUs and overstock | Monthly aged review, removals, bundles |
| Inbound placement | Single-destination shipments | Split shipments to recommended centers |
| Returns processing | Sizing and expectation gaps | Listing accuracy, sizing charts, better images |
| Ad cost per unit | Unallocated in most P&Ls | Allocate spend by ASIN, not by account |
Size tier engineering pays every single order
Fulfillment cost is driven by dimensional tier and unit weight. A package sitting just above a tier boundary pays the higher rate on every unit for the life of the SKU, which is why packaging redesign frequently returns more than any advertising optimization.
Measure your packed unit exactly as Amazon measures it, then look for the gap. Thinner corrugate, a flat mailer instead of a box, removing a void filler, or reorienting the product inside the pack are the usual wins. Test the drop performance before you commit, because a cheaper tier that raises damage rates costs more than it saves.
Storage and aged inventory: the quiet compounding cost
Storage is charged monthly and rises for units that age past thresholds, so a slow SKU pays rent indefinitely while contributing little. The discipline is a monthly review of days of supply and aged buckets, with a decision on every SKU that crosses the line: run a promotion, bundle it with a fast mover, remove it, or liquidate.
The mistake is waiting for the quarterly review. By then the surcharge has already applied twice and the recovery math is worse.
- Keep days of supply within a defined band rather than maximizing coverage
- Bundle slow units with fast movers instead of discounting them alone
- Remove or liquidate before the aged surcharge tier, not after
- Treat low-inventory conditions as a cost, not just a stockout risk
Returns are a listing problem more than a logistics problem
In apparel, footwear, and anything with a fit or expectation component, returns processing can erase the entire contribution margin of a SKU. Operational changes rarely fix it. Listing accuracy does.
Pull return reasons by ASIN, group them, and fix the top reason in the listing. If the top reason is size, the fix is a sizing chart and an explicit fit note in bullet one. If it is "not as described", the fix is images and specification text. If it is damage, the fix is packaging. Each fix compounds because it also raises review quality.
The review cadence that keeps margin honest
- Monthly: aged inventory, days of supply, return reasons for top 20 ASINs
- Quarterly: full per-unit P&L refresh and SKU rationalization decision
- On every fee schedule change: re-run the P&L before adjusting prices
- On every packaging change: re-measure the packed unit and confirm the tier
