Available-to-Promise (ATP)
Available-to-Promise (ATP) is the firmly committable availability of an item for a specific date: the quantity an ERP system can still promise to a new sales order from physical stock plus expected incoming supply, minus demand already reserved for other orders.
Available-to-Promise (ATP) describes the quantity of an item that can be firmly committed to a new sales order at a given point in time without jeopardizing already confirmed orders. ATP is therefore not raw inventory but a net figure: available physical stock plus firmly scheduled incoming supply (purchase orders, production orders) minus the quantities already reserved for other orders. In sales, the ATP result answers the central question "Can I deliver this quantity by this date?" – and provides the basis for reliable delivery commitments.
ATP is a core component of modern inventory management and ERP systems, tying together stock control, order processing and procurement into a dependable availability check. Without ATP, a sales team either works with unnecessarily conservative lead times or risks overselling, because the same stock is promised more than once. A correctly configured ATP logic is therefore the prerequisite for automatically quoting realistic delivery dates during the order process and for making the best possible use of available stock.
At a glance
- ATP = physical stock + planned incoming supply − reserved demand
- Answers: "Which quantity can I firmly commit for which date?"
- Prevents overselling and underpins reliable delivery commitments
- Date-specific: available today ≠ available on the requested date
- The CTP (Capable-to-Promise) extension factors in free production capacity
How does Available-to-Promise (ATP) work?
ATP calculates a committable quantity from several data sources in the ERP system. The basis is available stock – the physical inventory minus blocked quantities (blocked stock, quality inspection) and goods already reserved. Added to this are scheduled receipts: open purchase orders with the supplier and running production orders with their planned arrival date. From this sum the system subtracts the demand already committed through confirmed sales orders. The result is the freely available, committable quantity – and specifically in relation to a concrete date, not as a static figure.
The time dimension is decisive. An item may not be in stock today, yet still be available for the customer's requested date thanks to a goods receipt arriving in five days. ATP therefore calculates across a time axis and assigns receipts and demand to their respective dates. This way the system can make a firm commitment even when stock is currently zero – backed by a firmly scheduled inbound delivery.
The ATP formula and its components
Simplified: ATP = available stock + planned incoming supply − open demand. Available stock is the physical inventory without blocked and reserved quantities. Planned incoming supply is scheduled purchase orders and production orders. Open demand is the quantities already committed from confirmed orders. Because each of these figures is tied to a date, ATP is always a date-bound statement. Some systems additionally maintain a cumulative ATP value that is carried forward along the time axis and shows from which date which remaining quantity is still free.
Methods: discrete, cumulative and the ATP horizon
In practice, a distinction is made between discrete ATP, which shows availability for individual time windows (such as days or weeks), and cumulative ATP, which sums up free quantities across future periods and thereby brings them forward. In addition, an ATP horizon defines how far into the future planned receipts may be drawn on for commitments at all. These parameters control how aggressively or conservatively a company commits delivery dates.
Why Available-to-Promise (ATP) matters
The central benefit of ATP lies in the reliability of delivery commitments. If sales quotes a delivery date based on a clean ATP check, the risk that orders have to be cancelled, postponed or split into partial deliveries falls. This protects the customer relationship and reduces costly rework in order processing. Especially in e-commerce, where availability and lead time directly determine the purchase decision, a correct availability commitment is a direct competitive factor.
ATP also prevents the dreaded oversell: promising the same stock multiple times across different orders or sales channels. Anyone selling simultaneously via shop, marketplaces and classic sales needs a cross-channel ATP view so that three customers don't order the same last pallet. Conversely, ATP avoids unnecessarily long standard lead times: instead of scheduling conservatively across the board, the system also uses planned receipts and can therefore deliver earlier than a glance at pure inventory would suggest.
Available-to-Promise (ATP) in the ERP system
In the ERP system, ATP is not an isolated module but a cross-functional feature that links stock control, order processing, procurement and – at manufacturers – production planning. When a user creates an order line, the system runs the ATP check in the background and proposes a confirmed delivery date or a feasible delivery quantity. Once the customer confirms, the stock is reserved and is no longer available to future ATP calculations.
The value of ATP stands or falls with data quality. Incorrect stock levels, unmaintained replenishment lead times or unrealistic arrival dates lead to commitments that operations cannot keep. The prerequisite is therefore reliable stock control, kept in real time as far as possible, together with a clean link to open purchase orders and production orders. In multichannel scenarios, stock synchronization is added: all channels must draw on the same available quantity, otherwise exactly the double sales that ATP is meant to prevent will arise.
ATP versus CTP (Capable-to-Promise)
ATP checks against existing stock and already planned receipts – it therefore only commits what is already scheduled. Capable-to-Promise (CTP) goes one step further and factors in free production capacity and available material: if an item is neither in stock nor on order, CTP checks whether it can still be manufactured within the requested deadline. CTP is thus primarily relevant for make-to-order manufacturers, whereas pure traders usually get by with ATP.
Distinction: ATP vs. delivery capability and availability
ATP is often confused with related terms. Simple available stock is a snapshot without any time reference – it tells you what is free now, but nothing about future receipts or demand. Delivery capability describes more generally a company's ability to serve demand from stock, often as a metric (service level) over a period. ATP, by contrast, is the concrete, date- and order-specific commitment figure for a single inquiry.
Reserved stock must also be distinguished: as soon as ATP has committed a quantity to a confirmed order, it is reserved and removed from the committable pool. ATP is therefore the calculation step before the reservation. And safety stock feeds in indirectly: many systems net it out of available stock so that ATP does not commit all the way down to zero and a buffer for short-term demand is retained.
ATP in practice in the DACH mid-market
In the DACH mid-market, ATP is long no longer limited to large enterprises with SAP environments. Even lean cloud ERP and inventory management systems for retail and e-commerce now offer an availability check that takes stock, open purchase orders and reservations into account. The level of maturity varies widely, however: from a simple "available/not available" display to a date-accurate, cross-channel ATP calculation that considers incoming supply.
Decisive in practice are the configuration parameters: which stock types count as available, how far the planning horizon for receipts reaches, from which point a goods receipt is considered certain. These settings determine whether ATP commits rather optimistically or conservatively. A common mistake is to plan in incoming supply too generously and thereby commit dates that fail because of delayed deliveries. A dependable ATP configuration is therefore always a trade-off between maximum stock utilization and the reliability of the commitment.
Example
ATP check at an e-commerce retailer
A mid-sized online retailer sells a popular coffee machine via its own shop and two marketplaces. Physically, 40 units are in stock, 25 of them already reserved by confirmed orders. A delivery of 100 units arrives in six days. If a customer now requests 20 units for tomorrow, the ATP check reports only 15 units as immediately committable (40 − 25). For the remaining five units, the system moves the commitment to the goods receipt date in six days.
Because all three channels draw on the same ATP calculation, the same stock cannot be sold twice: as soon as the shop order is confirmed, the committable quantity also drops on the marketplaces. The retailer thus quotes realistic delivery dates at all times, uses the expected inbound supply for earlier commitments and avoids overselling without having to communicate blanket long lead times.
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