There are many calorie requirement calculators on the Internet.
Many factors influence our demand: age, health condition, height, body weight, physical activity, gender, etc.
Free calculators will probably require your weight, height, age and physical activity. When you calculate it, you will +/- know how many calories you need to maintain your weight.
Any additional calories above that may be stored as fat tissue, but this is information on separate topics.
Lifestyle and food culture obviously also influence how much and how you eat.
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