The on-hand inventory balance minus allocations, reservations, backorders, and (usually) quantities held for quality problems. Often called ‘beginning available balance’. Synonyms: Beginning Available Balance, Net Inventory. Available to Promise (ATP): The uncommitted portion of a company’s inventory and planned production maintained in the master schedule to support customer-order promising. The ATP quantity is the uncommitted inventory balance in the first period and is normally calculated for each period in which an MPS receipt is scheduled. In the first period, ATP includes on-hand inventory less customer orders that are due and overdue. Three methods of calculation are used: discrete ATP, cumulative ATP with lookahead, and cumulative ATP without lookahead.