Calorie needs vary from person to person. This will depend on a huge number of factors, this is where one size fits all approach such as Slimming World and Weightwatchers fall down because they have an inability to tailor for an individual's needs.
Your calorie needs are dependant on the following-
Your exercise- i.e the duration, format and intensity
Your occupation- Are you someone who is sat at a desk or are you someone that is active during your job?
Genetics- Some people naturally burn more calories than others
Lifestyle- Do you have more of a sedentary lifestyle like do you enjoy sitting down reading a book or are you someone who is more active as in you like to go swimming, mountain climbing etc.
Medications- There are certain medications that can interfere with your metabolism
Body composition- Your height etc
Sleep- How much sleep that you get
Unless you are going to an actual lab then there will always be guesstimates that you work from when it comes to calories. These will be our best guess to start off with and then we can adjust depending on our results.
There are a number of ways that we can do this-
We could go into a lab but most of us aren’t going to do this.
To track your diet and daily weight changes for 2 weeks.
You could use equations/calculations to guesstimate how many calories you need based on your inputs such as what your height is etc. You can also ask your PT/Coach to help you with this.
To multiply your bodyweight by a certain number. This varies in terms of inputs but people have found that it gets pretty close for them in terms of the best accuracy that you can get if you’re not going to go into a lab to do it. This is also the easiest way to calculate how many calories that you should be eating.
Calories- A rough and ready method
Multiply what your body weight is in pounds(lbs) x by 14-16 calories to figure out the calories that you need for maintenance.
Maintenance calories are where you are reaching calorie output with calorie input in order to maintain a stable weight.
If you are an active male then you would probably want to multiply it by 16 but if you are a sedentary female then you would probably want to multiply it by 14.
If you are looking to diet then it will be somewhere between 10-12 calories per lb of your body weight. So here is an example of working this out-
If you were looking to maintain your weight and you are 100 lbs then you would multiply this by 14 or 16 which would be 1,400 calories- 1,600 calories.
If you were looking to diet then you would multiply the 100 lb of body weight by 10 and then it would be 1,000-1,200 calories a day, this would then create a calorie deficit.
If you were a 200 lb person then you would double the numbers.
Here’s another example just to try to help you in case you’re feeling a little confused with the numbers etc- If you are 70kg then this is 154 lbs which are 11 stone. That 154 lbs x 10-12 then = 1,540-1848 calories.