What Is a Backorder? Warehouse Definition and Examples

A backorder is an order for a product that cannot be fulfilled immediately because it is out of stock, but the seller accepts the order and will ship the item once inventory is replenished. Backorders let customers reserve items and help businesses manage demand, but they typically cause delayed delivery times and require clear communication about expected restock dates.

Backorder refers to an ordered quantity that cannot ship immediately because inventory is unavailable. In warehouses and fulfillment operations, a backorder identifies items sold or requested by customers that are temporarily out of stock and awaiting replenishment or alternate fulfillment.

Backorders are a normal part of inventory-driven businesses but vary widely in scope and consequence depending on product value, customer expectations, and replenishment speed. A single SKU with high demand and long supplier lead time produces more meaningful operational challenges than an occasional backorder on low-velocity items. Warehouse managers must treat backorders as both inventory and customer-service events: they affect physical workflow, accounting, and the buyer experience.

Why Backorders Occur

Backorders come from mismatches between demand and available stock. Common causes include inaccurate forecasting, late supplier shipments, production delays, sudden demand spikes, inventory counting errors, and mislocated stock in the warehouse. Sales channels that do not sync in real time with the warehouse management system (WMS) — for example separate marketplaces, a physical store, and a website — create oversell risk, which converts into backorders.

How Backorders Are Recorded And Tracked

Most modern WMS or inventory management systems create a backorder record when an order line cannot be filled immediately. The record typically includes the original order, quantity backordered, expected replenishment date, and status (pending, partial shipped, canceled). Systems may flag the order for automatic partial shipment or hold the entire order until fulfillment is complete. Integrations with the ERP and order management systems ensure accounting and customer-service teams see consistent status.

Operational Impacts

Backorders influence several operational areas simultaneously.

• Receiving and Putaway: Replenishment receipts trigger workflows to satisfy backorders; priority may be given to SKUs with outstanding backorders when staging inbound receipts.
• Picking and Packing: Backorders create partial picks and split shipments. Pick waves may need to exclude backordered quantities or schedule re-picks once stock arrives.
• Customer Service: Agents need accurate ETAs and cancellation options; poor communication increases chargebacks and returns.
• Space Planning: Unexpected replenishment priorities can alter slotting and cause temporary congestion at packing stations.

Financial And Reporting Considerations

From accounting and sales perspectives, backorders raise questions about revenue recognition, fulfillment costs, and forecasting accuracy. Finance teams track backorder rates as an indicator of lost or delayed revenue. Common KPIs include backorder rate (percentage of orders with any backordered line), fill rate (percentage of demand immediately satisfied), and days to fulfillment for backordered items.

Customer Experience And Communication

How you communicate about a backorder determines customer satisfaction. Clear ETA estimates, proactive notifications, and options to cancel or accept partial shipments reduce complaints. Some retailers offer discounts, expedited shipping on backordered items once available, or substitution options. For B2B customers, purchase order acknowledgements should update expected ship dates automatically through EDI or portal updates.

When Partial Shipment Is Appropriate

Deciding whether to ship a partial order while other items are backordered involves weighing customer expectations, shipping costs, and operational complexity. Ship partials when the remaining items are low value and customers prefer immediate receipt. Hold for full shipment when the order is bundled, or when shipping costs and returns handling for multiple shipments exceed customer goodwill.

• Label: Partial shipment advantage: Improves customer satisfaction for high-priority items.
• Label: Partial shipment drawback: Increases shipping and handling costs and may complicate returns.
• Label: Hold-for-complete advantage: Simplifies logistics and reduces freight spend.
• Label: Hold-for-complete drawback: Longer lead time for the customer.

Practical Examples

Example 1 — Consumer electronics seller: A popular speaker sells out during a promotion. The WMS flags orders as backordered and automatically sends an email with a projected ship date 14 days later when the replenishment PO is due. The warehouse schedules inbound receipts to be staged for immediate picking to clear the backorder queue.

Example 2 — Industrial supplier: A pump part is out due to a supplier delay. Orders are split: available items ship immediately while backordered parts remain open. The account manager contacts the customer offering a temporary substitute to avoid downtime, creating a cross-charge agreement for the replacement part.

How To Reduce Backorder Frequency

Reducing backorders combines demand planning, safety stock policies, supplier management, and systems integration. Forecast using SKU-level history and incorporate lead-time variability. Set safety stock levels based on desired service level and supplier reliability. Use purchase order alerts and vendor scorecards to address late shipments. Integrate sales channels with the WMS to prevent oversells and consider drop-shipping or multi-sourcing for critical SKUs.

• Demand Forecasting: Use rolling forecasts and adjust promotions to avoid sudden spikes that create backorders.
• Safety Stock: Calculate safety stock using lead-time variability and service-level targets for each SKU.
• Supplier Diversification: Maintain backup sources for high-turn items or use local suppliers for short-term bridging stock.

In short, the Backorder is an inventory and customer-service signal that an ordered quantity cannot ship immediately because inventory is unavailable. Treated properly with clear policies, system flags, and proactive customer communication, backorders can be managed to minimize operational disruption and preserve customer trust.