if you're actually weighing the chicken raw, your best bet would be to manually enter the info from the package [or use another usda source for raw chicken]. most of the change of the cooking weight of chicken is water. so if you like your chicken drier than most people, your chicken will yield a lighter cooked weight. just like if you cook your chicken a little moister, you'll have heavier chicken when you're done cooking it. so if you're weighing it raw, just use raw nutrition info. nutritiondata.com
is a pretty good source for raw info if it's not on the package.