How many Calories do you ACTUALLY need to eat per day? (Increasing Muscle Mass while losing Body Fat)

The Energy requirement of an individual is based on multiple factors: 

1. Type of training/exercise,
2. Intensity of training/exercise,
3. Frequency of training/exercise,
4. Current body composition, and 
5. Weight loss goal.

Aim to achieve a balance your choices for:

1. Satisfied appetite, 
2. Healthy weight, 
3. A positive mood, 
4. Myofibrillar Hypertrophy,
5. Low body fat percentage (~10%),
6. General overall good health & well-being.

Basal metabolic rate (BMR) -

1. BMR is a measurement of how many calories your body burns at rest.
2. The human body uses 86% of the BMR calories to keep up with its natural processes at rest, and 14% in the process of digestion.
3. Athletes require the proper nutrition and fuel to perform. This varies depending on the sport and the individual.

The following Sterling-Pasmore BMR equation is based on a person's body composition:

1. You need 13.8 calories to support 1lb of lean muscle mass, i.e.,
   You need 30.6 calories to support 1kg of lean muscle mass.
2. To calculate your BMR accurately, you need to know your Scale weight & Body fat %.
3. Fat mass = Body fat % x Scale weight
   Fat mass = Scale weight - Lean body mass
4. Lean body mass = Scale weight - Fat mass,
   Now, BMR= Lean body mass (lbs) x 13.8 calories = Lean body mass (kgs) x 30.6 calories
5. Lean body mass = (Scale weight) - (Body fat % x Scale weight)
   Lean body mass = (Scale weight) x (1 - Body fat %)
6. Example,
   If your desired Body Fat % is ~10%,
   It can be concluded that, your desired Lean body mass can be calculated by
   Lean body mass = (Scale weight) x (1 - 10%) = Scale weight x (1 - 0.1) = Scale weight x 0.9.

The following Harris Benedict formulae are used to account for the calories burned during exercise/physical activities:

Maintaining Average Muscle Mass -

1. BMR x 1.200 for no exercise (low-intensity activities and leisure)
   sedentary lifestyle throughout the week @ 30-50% MH
2. BMR x 1.375 for light exercise (leisurely walking, golfing, house chores)
   3-4 days/week for 30-50 minutes/session @ 50-60% MHR

Maintaining Ideal Muscle Mass -

1. BMR x 1.550 for moderate exercise (moderate exercise/sports)
   3-5 days/week for 30-60 minutes/session @ 60-70% MHR
2. BMR x 1.725 for intense exercise (hard exercise/sports)
   6-7 days/week for 45-60 minutes/session @ 70-85% MHR

 Over Workout (Overstresses the Body) -

1. BMR x 1.900 for the extreme exercise (heavy manual labor/lifting, endurance/sports athletes)
   6-7 days/week for 90+ minutes/session @ 85-100% MHR

Bottom line -

1. Most of us today are living a sedentary lifestyle throughout the day, so for the most of us our daily calorie requirement is BMR x 1.2. 
2. If you wish to lose bodyfat while without exercising, i.e., while continuing your sedentary lifestyle, check out this article.
3. If you want to increase your muscle mass to its ideal levels, you should at least moderately exercise every alternate day, by performing High-Intensity Interval Training (HIIT) &/or Bodyweight Training (BWT).
4. This moderate exercise routine pushes our daily calorie requirement to BMR x 1.55, which is 22% higher than the calories required for a sedentary lifestyle.
5. This moderate but efficient exercise is near prefect, as it results in the maximum physical & mental benefits, with the least investment of time & effort, when compared to other exercises.
6. If you exercise more than (3-6 days/week for 30-60 minutes/session) in any way at all, you are not actually building "muscle fibers", you are instead doing one of the following:
   
   1. Burning your muscles for energy to be used during the extra workouts,
   2. Increasing the sarcoplasm in your muscles and not actually increasing your muscle strength,
   3. Taxing your whole body into stress by forcing it to work more than it effectively "needs" to,
   4. Increasing the probability of injuries, as, your body is being forced to work at a rate higher than its rate of repairing itself.

Note -If you are doing sports or if your job requires the extra physical work from you, its "OK" as long as its beneficial for your career, family, and other things that may be more important to you.

Reference -
http://www.bodybuilding.com/fun/calorie-know-how-get-equation-right-to-get-results.htm