To determine how many calories you need to lose weight or build muscle you first need to determine you basal metabolic rate (BMR, Harris Benedict Equation) . This is simply the amount of calories you need to survive with no physical activity ie laying in bed all day.
This is a formula based on your gender, age, weight & height. There is a calculator here.
Once calculated you then multiple this by a factor based on your activity level.
|Little to no exercise||1.2|
|Light exercise (1–3 days per week)||1.375|
|Moderate exercise (3–5 days per week)||1.55|
|Heavy exercise (6–7 days per week)||1.725|
|Very heavy exercise (twice per day, extra heavy workouts)||1.9|
This is your base number of calories to maintain your current body weight. In order to lose weight you need to consume less calories than your base (300-500) and to gain weight you need to consume additional calories above your base rate (200-300).
Male, 25, 5ft 10in, 80kg
His BMR is 1887 calories. Exercising 5 days per week his base calories are 2925 per day.
If he wishes to lose weight he needs to consume less than 2925 (1887 x 1.55) so he should aim for roughly 2625 per day. If he wishes to gain weight he needs to consume above this amount and should aim for roughly 3225 calories per day.
https://youtu.be/UKIuW_-03wQ – Michael Kory Fitness