The calculator uses the Harris Benedict equation, with the appropriate activity multipliers included, to punch out your total daily energy expenditure (TDEE). From there, it subtracts and adds calories to your daily intake to ensure you are eating the right amount of calories for your specific goal. The result is an average calorie intake for the info that you entered and everyone will be slightly different therefore a personalised approach should be considered.
If you’re a classic hard gainer (ectomorph), feel like you have a particularly hard time gaining weight, or want to maintain muscle, consider adding an additional calories to your results.
For people of medium or large build—mesomorphs and endomorphs you could lower the calories slightly, but don’t hesitate to increase that number if you’re worried about losing too much weight too quickly. In the end, you know your body best.