The Business Central reservation engine

The reservation engine in Business Central links a piece of supply (inventory on hand, an inbound purchase order, a production order, a transfer order) to a specific demand (a sales order line, a production component, a service order). Reservations are how the system promises one customer that this particular stock will be reserved for their order rather than the next person who logs in.

Why reserve at all

Without reservations, a sales order line just expresses demand against a pool — and that pool is up for grabs by anyone else who picks faster. Reserving converts the promise into a binding allocation that survives until the order is shipped or the reservation is cancelled.

Automatic, optional, never

Each item has a Reserve field with three settings: Never (no reservations allowed), Optional (users reserve manually when needed, the default), and Always (every demand line is reserved as it's created, blocking creation if no supply exists). Most companies use Optional and reserve selectively.

Manual reservations

From a sales order line, users open the Reservation Entries page and pick which supply to bind to: on-hand quantity, an inbound purchase, a production order, an assembly order, a transfer order. The reservation entry stores the link. Posting the source consumes the reservation.

Order-to-order binding

A stronger form of reservation, used for make-to-order and configure-to-order, where the supply is created specifically for the demand. The link is bidirectional — if the sales order quantity changes, the production order changes; if the production order is cancelled, the demand becomes unreserved. Order-to-order is the operating model for many engineer-to-order shops.

Item tracking and reservations

When items have lot or serial numbers, reservations can be at the tracking level (this serial number, this lot) or at the quantity level. Specific tracking reservations are common in pharma, food, and high-value goods.

Reservations and planning

Reserved supply is visible to MRP and is excluded from the available-to-promise pool. The planning worksheet honours reservations and won't suggest cancelling a reserved supply order.

Trade-offs

Heavy reservation discipline gives reliable delivery promises but increases administrative load. Many companies start with Optional and reserve only for committed orders above a value or with delivery commitments.