Your fitbit should give average calories burned per day, ideally from data gathered over several weeks. This gives your baseline relative to whether you need to gain weight or lose weight, or else keep your current weight? Likewise, take into account what are your health objectives, challenges etc. might be. Also matters what you eat since not every calorie is the same as the next. e.g. calories from processed foods generally don't provide the same nutrition as from whole foods and meals prepared from them. Again, all relative to your circumstance and objectives etc.
