My opinion is that you have all the calculation you need with Fitbit (not an advertisement, I'm just a user). Assuming you have a Fitbit device and its app, Fitbit will estimate your calories burned. If you log your meals in the App, you will be able to see the deficits over time. The thing I really like is how you can set a deficit goal, and the app will tell you where you are relative to that goal.
To lose a pound a week, create a 500 daily calorie deficit. To lose two pounds a week, create a 1,000 daily calorie deficit. This is based on the well-accepted theory that to lose a pound, you must create a 3,500 calorie deficit, independent of age, weight and gender.
