When you enter an SAP environment for the first time, especially in sales or supply chain roles, you quickly meet Available-to-Promise, known as ATP. This function determines whether you can commit to delivering a specific quantity of material to a customer by a requested date, based on current stock and expected incoming supplies. In daily operations, ATP acts as the control point that stops over-promising and helps avoid customer disappointment from unfulfilled deliveries. Getting the setup correct supports smooth processes in manufacturing plants or distribution centers, where inventory changes rapidly from production output or vendor arrivals. For those starting out in SAP, it helps to see ATP as a calculated check that combines data from inventory, procurement, and production to deliver a dependable availability picture. The following sections explain the core mechanics, configuration, and practical use of ATP across standard SAP systems.In standard SAP setups, ATP runs automatically during sales order creation or when planning materials, making sure delivery commitments match actual capabilities. Consider a customer placing an order for 100 units of a component while only 50 sit in unrestricted stock and another 60 arrive via purchase order the following week—the system confirms the immediate 50 and schedules the balance for later, avoiding a full promise that cannot be met. This matters greatly in sectors like retail distribution or automotive supply, where one delay often triggers broader production stops downstream. Consultants explain to project teams that ATP follows defined rules, reviewing existing stock levels, planned receipts such as production orders, and current commitments including other sales orders or reservations. While SAP has refined ATP over time—from simpler checks in SAP ECC to more capable versions in SAP S/4HANA—the central purpose stays consistent: delivering reliable confirmations that keep operations stable.