Am i over or under estimating calories?

Hi everyone, I have recently started a diet and am wondering if i am over or underestimating my intake. For example, the raw chicken breast package i have states that it has 100 calories per 100 grams of chicken breast. The whole package is 0.841 kg; therefore, it should have 841 calories, correct? When i cook it (i barely use any oil), does the chicken itself have fewer calories? In other words, once cooked, will the chicken have something like 700 calories and less protein than what is stated on the package? Thanks in advance