ATP is know as available to promise quantities and it is Calculated as below. Ware house stock + planned receipts – Planned issues = ATP quantities. Ex1. 100 + 50 -75 = 75 is ATP Quantity Any remaining open quantity in the movement is regarded as the ATP quantity and can be used to fulfill the next Requirement. Ex2. 25 + 100 -150 = -25 ATP Quantity, In this case the system try to capture the stock from other inward movement and try and match the order quantity 150.and even this is not available and partially met then the system shows the negative ATP Quantities in the requirement line. During the availability check the system determines the ATP quantities for the material and the plant. The system behaves in performing the availability check based on how the availability check is set in customizing. This can be viewed in the sales order, over view screen procurement and you can see the confirmed quantity and ATP Quantity. Availability check: Stock checks which is automatically carried out after every goods movement and which should prevent the book inventory balance of physical stock (for example, available stock) from reaching zero. types of Availability checks 1. Against ATP 2. Against product allocation 3. Against planning. Availability check is based on checking group, Requirement class, and Requirement type and schedule line category.