Yield Percent is the percent of the As-Purchased Quantity that is edible after prepartion.  Ex. You cook a particular food and it's 25% lighter, then the CY% is 75%.  If you cook rice and it make twice as much, then the CY% would be 150%.  If you're unsure, leave it 100%.  We factor this into your grocery list so that you buy and prep the right amount of food.  Often times, people dont buy enough food or too much food than their meal plan calls for and this helps make everything more accurate.  These percentages can be adjusted at any time by you.  The Yield Prct Database is a guide to what most foods yield percentage is and should be used as a reference.  Again, nothing is more accurate than your own experiences.