Reservations and How They Interact with Picking

Two orders for the same item, both legitimate, both wanting the same units of stock, is an ordinary Tuesday in any warehouse selling anything popular. Reservation is the mechanism that decides which order actually gets to claim which units — and it’s worth understanding precisely, because it isn’t a soft priority hint. It’s an active constraint a pick has to honor, and it can quietly reduce what a picker is allowed to take even when there’s plenty of physical stock sitting right in front of them.

A reservation is a claim on specific supply, not a note on a demand

Reserving an item ties a specific quantity of supply — sometimes a specific lot or serial number, sometimes just a quantity of the item in general — to a specific demand line, so that quantity can’t be double-promised to a second order. It can be done from a sales order, purchase order, service order, assembly order, transfer order, or production order, and it can draw from inventory already on hand or from inbound supply that hasn’t arrived yet.

There’s a real distinction Business Central draws between the two flavors of reservation, and it matters for how tightly a reservation constrains a pick: reserving from any quantity of item X on hand is a nonspecific reservation — a claim on the item in general. Reserving specifically from the quantity of item X that belongs to lot X (or serial X) is a specific reservation — a claim on that exact tracked unit, not just the item family it belongs to. Specific reservation matters most in exactly the cases where it’s tempting to assume “any unit will do” and it genuinely won’t — a production line that needs components from a particular lot to stay consistent with an earlier run, or a customer who has specifically asked for a particular serial number.

Reserving in practice — one line at a time, or in bulk

The ordinary path is manual: open a document line’s Reserve action, and either let Business Central Auto Reserve against available supply, or explicitly Reserve from Current Line against a specific entry the user selects. For a tracked item, reserving a specific lot or serial routes through one extra step — the Item Tracking List page — where the exact tracked number gets selected before the reservation is created against it.

For higher volume, the Reservation Worksheet exists to reserve and allocate incoming supply in bulk against a pool of demand gathered with Get Demand to Reserve, using one of three allocation policies when supply can’t cover every demand line in full: Basic (No Conflicts) only allocates a demand line if it can be fully covered with no competition; Equally splits available stock proportionally across competing demands; By Customer Priority favors higher-priority customers first when stock runs short. Which policy a business runs is itself a real operational decision — a company doing production allocation weekly and sales reservation daily, for instance, might run two different reservation-worksheet batches with two different policies for two different purposes.

What a reservation actually blocks at pick time

This is where reservation stops being a planning artifact and becomes something a pick has to respect mechanically. Business Central’s own warehouse-availability logic treats reserved demand as strictly higher priority than unreserved demand, specifically so that picking for an unreserved order can never crowd out a reservation that’s supposed to be protected. The practical rule: quantities already reserved for pending outbound shipments are subtracted out of what’s available to pick for anything else — so a second order competing for the same item can be told there’s nothing to pick, even while units of that item are still physically sitting in a pick bin, because those particular units already belong, on paper, to someone else’s order.

It cuts in a genuinely counterintuitive direction worth naming plainly: reserving more than what’s currently available in active pick bins for another order can produce an error, even when the item’s total on-hand quantity, spread across bulk storage bins, looks more than sufficient. If five units sit in pick bins and a hundred more sit in put-away bins further back, reserving six units for a second order can fail — not because the item is genuinely out of stock, but because the additional unit isn’t yet in a bin picking is allowed to draw from. The fix in that situation usually isn’t “there’s no stock” — it’s “replenish the pick face from bulk storage first.”

The asymmetry between “available to pick” and “available to reserve”

It’s tempting to assume these are the same number viewed two different ways. They aren’t, and the difference is deliberate. Quantity available to pick is calculated as the quantity physically sitting in pick bins, minus whatever’s already committed to existing picks and movements, minus whatever’s reserved either in those pick bins or on those existing picks and movements — a genuinely narrow, floor-level number scoped to bins actually designated for picking.

Quantity available to reserve is calculated far more broadly: total quantity on hand across the whole location, minus quantity already on outbound picks and movements, minus quantity already reserved, minus quantity sitting in outbound-type bins (shipment bins, to-production bins, open shop floor bins, to-assembly bins, and the adjustment bin) — which means it includes stock in ordinary storage and put-away bins that picking itself can’t touch yet. A number can be simultaneously “available to reserve” and “not currently available to pick,” and that isn’t a bug or a sync lag — it’s an accurate description of two different physical facts: whether the business is entitled to promise the stock to someone, and whether a picker standing at a pick face can lay hands on it this minute.

Blocked, dedicated, and quarantined stock never enter the count at all

Reservation math also has to account for stock that’s technically on hand but genuinely unavailable for a different reason entirely. A blocked lot or serial number — one flagged through its own information card as unfit for further transactions — is excluded from pickable quantity outright, the same way stock sitting in a dedicated bin reserved for a different item, or a locked bin, is excluded. These exclusions happen before reservation priority is even applied; a reservation can’t claim stock that was never eligible to be picked in the first place.

Why this matters more than it looks like it should

The practical upshot for anyone working a floor, or building anything that scans against one, is that “how much of this item do we have” is not one number. It’s at least three: total on hand, available to reserve, and available to pick — and a scan-driven operation that only checks the first of those will occasionally hand an operator a task the system was never actually going to let post, because the units in front of them on a shelf already belong, on paper, to someone else’s order. Reservation isn’t a courtesy Business Central extends to whoever asked first — it’s an enforced allocation the picking logic actively defends, right down to refusing an otherwise perfectly reasonable-looking pick to protect it.

Where this goes next

Reservation and item tracking are two halves of the same underlying mechanism for a tracked item — see item tracking in Business Central, explained for where a lot or serial number actually lives, which is exactly what a specific reservation claims against. For how FEFO’s own sort order interacts with which lot a pick is even allowed to consider, see FEFO vs. FIFO, explained. For the document-level mechanics of turning an available quantity into an actual, physical pick, see inventory pick vs. warehouse pick, explained.

Key terms

New to the vocabulary? Reservation, Lot number, Serial number, and Pick are defined in the glossary.

Further reading — Microsoft Learn

How to Reserve Items — specific vs. nonspecific reservation, and the Reservation Worksheet’s allocation policies, in full. Design Details: Availability in the Warehouse — the exact calculations behind quantity available to pick and quantity available to reserve.