A calculation based on the available-to-promise figure in the master schedule. For the first period, the ATP is the sum of the beginning inventory plus the MPS quantity minus backlo g for all periods until the item is master scheduled again. For all other periods, if a quantity has been scheduled for that time period then the ATP is this quantity minus all customer commitments for this and other periods until another quantity is scheduled in the MPS. For those periods where the quantity scheduled is zero, the ATP is zero (even if deliveries have been promised). The promised customer commitments are accumulated and shown in the period where the item was most recently scheduled. Also see: Available-to- Promise.