To calculate the number of calories you need per day, you can use the Harris-Benedict equation. This equation takes into account your basal metabolic rate (BMR) and activity level.

For men: BMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) - (5.677 × age in years)

For women: BMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) - (4.330 × age in years)

Once you have calculated your BMR, you multiply it by an activity factor:

• Sedentary (little to no exercise): BMR × 1.2
• Lightly active (light exercise/sports 1-3 days a week): BMR × 1.375
• Moderately active (moderate exercise/sports 3-5 days a week): BMR × 1.55
• Very active (hard exercise/sports 6-7 days a week): BMR × 1.725
• Extra active (very hard exercise/sports & physical job or 2x training): BMR × 1.9

This calculation gives you an estimate of how many calories you need to maintain your current weight. If you want to lose weight, you'd eat fewer calories than this number, and if you want to gain weight, you'd eat more.

Remember, these are just estimates, and individual factors like metabolism, muscle mass, and overall health can affect your actual calorie needs. It's always a good idea to consult with a healthcare professional or nutritionist for personalized advice.