How daily calorie needs are calculated
The calculator works in three steps. First it finds your BMR with the Mifflin-St Jeor equation. Then it multiplies by an activity factor to get your maintenance calories (TDEE). Finally it adjusts for your goal — subtracting calories to lose weight or adding them to gain:
target = (BMR × activity factor) + goal adjustment
500 kcal/day deficit ≈ 0.45 kg (1 lb) lost per week
Worked example
A 30-year-old man, 178 cm, 75 kg, moderately active, aiming to lose 1 lb/week:
BMR: ≈ 1,718 kcal/day.
Maintenance (×1.55): ≈ 2,663 kcal/day.
Minus 500: ≈ 2,163 kcal/day to lose about a pound a week.
Eating safely
Very low intakes are counter-productive and can be unsafe. As a common floor, adults are often advised not to drop below about 1,500 kcal/day for men and 1,200 for women without medical supervision. The calculator flags targets that fall below these.
Note: these numbers are estimates for general guidance, not medical advice. Activity level, body composition and health conditions all matter — talk to a doctor or dietitian before any significant diet change.