What is reserved inventory and why does Amazon reserve units?
Reserved inventory shows up in your Seller Central inventory reports as units that are physically in Amazon’s warehouses but unavailable for immediate sale. Amazon reserves units for three reasons: a customer order is pending shipment (FC Processing), units are being transferred between fulfillment centers (FC Transfer), and units are being evaluated as part of a customer return (Customer Order).
The key formula for understanding your sellable position: Available units = Total on-hand minus Reserved minus Unfulfillable. Only available units can fulfill new customer orders. If you see your available count dropping while total on-hand stays flat, rising reserved inventory is the cause.
Reserved inventory typically resolves itself within 1 to 5 days. FC Processing reservations clear once the order ships (usually same day or next day). FC Transfers take 3 to 7 days as Amazon moves stock between warehouses. Customer return reservations can take 5 to 45 days depending on the return inspection timeline. If reserved units stay stuck beyond 7 days for orders or 14 days for transfers, something is likely wrong and you should open a Seller Support case.
Reserved inventory categories
| Reserved type | What it means | Typical duration | Action needed? |
|---|---|---|---|
| FC Processing | Order is being picked, packed, or shipped | 1 to 2 days | No, normal operations |
| FC Transfer | Units moving between Amazon warehouses | 3 to 7 days | Investigate if over 14 days |
| Customer Order | Return being inspected or processed | 5 to 45 days | Open case if over 45 days |
Example: reserved inventory and reorder timing
A seller doing $1.4M with 20 ASINs checks inventory on a Monday morning. One top-selling ASIN (ASP $45, 18 units/day) shows: Total on-hand: 312, Reserved: 87, Unfulfillable: 4, Available: 221. Days of supply based on available units: 221 / 18 = 12.3 days. But if the seller calculates days of supply using total on-hand (312 / 18 = 17.3 days), they get a 5-day cushion that does not actually exist.
Those 87 reserved units break down as: 24 in FC Processing (will resolve today), 51 in FC Transfer (arriving at destination FC in 3 to 5 days), and 12 in Customer Order returns (will take 7 to 14 days to process). Of the 51 transfer units, roughly 40 will become available within the week. So realistic available inventory by Friday: 221 + 24 + 40 = 285, minus 5 days of sales (90 units) = 195. That is 10.8 days of supply, not the 17.3 days the total on-hand number suggests.
This is why reorder calculations must use available inventory, not total on-hand. Ignoring reserved inventory is one of the most common causes of unexpected stockouts among $1M+ sellers.
Common mistakes
- Using total on-hand instead of available units for reorder calculations. Reserved units are not sellable right now. A 30% reserved rate on a fast-moving ASIN can create a 5-day gap between perceived and actual days of supply. Always base reorder triggers on available inventory.
- Ignoring FC Transfer reservations that exceed 14 days. Transfers should complete within 7 days. Units stuck in transfer for 14+ days may be lost in transit. Open a Seller Support case to get them investigated and potentially reimbursed.
- Panicking about high reserved counts during peak sales days. Reserved inventory spikes during Prime Day and Black Friday are normal because order volume is higher. FC Processing reservations clear within 24 hours. High reserved counts only warrant concern if they persist for multiple days outside of peak events.