Prime Day requires getting inventory into FBA three to four weeks before the event. Amazon stops accepting new inbound on a hard deadline — typically one to two weeks before the start of the event — and anything that has not checked in by then will not be available to fulfill orders during the sale window. Miss the cutoff and you have a product that is technically in-stock at your warehouse and completely unavailable to your customers.
For brands with inventory in multiple warehouse locations, the decision of which warehouse to ship from for those pre-Prime Day sends is not trivial. It affects check-in timing, freight cost, and whether your supply limits work for you or against you. For Our Place, with warehouses across California, Texas, Pennsylvania, Illinois, Canada, the UK, and Australia, this decision comes up every Prime Day prep cycle.
The rule the team runs is California first, always, for Prime Day FBA allocation.
Why California
Three reasons, in order of impact.
Check-in speed. California warehouses feed into West Coast Amazon FCs — primarily in the Inland Empire and surrounding areas — that process high inbound volumes from the most established freight lanes in the US. The combination of high lane utilization and strong inbound history at those FCs means inventory sent from California checks in faster than equivalent inventory sent from Midwest or East Coast origins. In the three to four weeks before Prime Day, check-in speed is not a nice-to-have. An inbound shipment that takes seven days to check in instead of five is two days of available supply headroom gone. At peak volumes, that matters.
Freight cost. California warehouses have more competitive outbound freight rates for oversized items to West Coast FCs than Pennsylvania or Illinois warehouses have to their nearest equivalent FCs. Wonder Ovens and Dream Cookers are expensive to ship. On high-volume Prime Day sends, the per-unit freight difference between a California origin and a Midwest origin adds up quickly. At 5,000-unit shipment sizes, a $0.50 per unit freight difference is $2,500 per send.
Supply limit headroom. Amazon's supply limit calculations are partly based on inbound history at specific FCs. The California warehouses — CAO2 and CAO3 specifically — had the most established inbound history with the relevant West Coast FCs. That history translated into better supply limit utilization for Prime Day sends. When the team needed to maximize how much inventory it could move into FBA in the weeks before the event, starting from the warehouses with the best established send-and-receive history was the path with the least friction.
How to apply this if your warehouses are elsewhere
The California rule is not about California specifically. It is about identifying which of your warehouse locations has the three relevant advantages — fastest FC check-in, lowest freight per unit to the relevant FC, best supply limit history — and making that location the default for time-sensitive FBA allocation.
If your warehouses are in the Southeast and you have the strongest inbound history with Mid-Atlantic FCs, the equivalent rule for your operation might be Virginia first. If you have a warehouse in Memphis with established lanes into the Memphis FC, that might be your default.
The point is to pick the decision in advance, write it down as a rule, and stop debating it each time. The worst version of this decision-making process is a weekly shipment planning meeting where someone says "should we send from Texas or California this time" and the team spends 20 minutes on a choice that should have been standardized six months ago.
The routing override
Amazon will recommend against this rule. Its inbound routing tool will frequently direct you to send from whatever warehouse is nearest to the destination FC it wants to use, which will often not be California. Follow your own logic, not Amazon's.
The step is straightforward. When creating a shipment in Seller Central, Amazon's routing tool will suggest a source location. You override that suggestion and select your preferred warehouse manually. This is a permitted action — Amazon's routing recommendation is advisory, not mandatory. The only scenario where overriding it creates problems is if your preferred warehouse lacks the physical ability to process the shipment quantity in the required timeframe, which is a logistics constraint to solve separately.
The timing question
Getting the timing right matters as much as the sourcing decision. The Prime Day FBA receiving cutoff is Amazon's deadline, but FC check-in times add their own buffer requirement on top.
For oversized items from California to West Coast FCs, transit is typically four to six days plus a two to four day FC receiving and check-in window. Call it ten days from warehouse departure to FBA available inventory under normal receiving speeds. In the weeks before Prime Day, Amazon's receiving gets slower, not faster — the FCs are processing an unusually high inbound volume. Build in an extra three to five days of buffer against the standard timeline.
Working backward: if the Prime Day receiving cutoff is July 1st, the last safe warehouse departure date for a California send with a ten-day normal transit and three-day peak buffer is June 18th. Any departure after that is a risk. The earlier you send, the more control you have over whether inventory is available when the event starts.
Send from California. Send early. The rest follows.
