Your resting energy use is estimated with the Mifflin–St Jeor equation, the most accurate predictive formula for adults in independent reviews (Frankenfield et al., J Am Diet Assoc, 2005). It's multiplied by a standard activity factor to estimate your daily needs.

Fat-loss targets use a moderate deficit of 10–20%, which keeps weight loss within the 0.5–1 kg a week that health services such as the HSE and NHS recommend. Your calories are never set below your estimated resting needs, and never below 1,200 kcal (women) or 1,500 kcal (men). Muscle-gain targets use a small surplus of 5–10% to limit fat gain.

Protein is set at 1.6–2.2 g per kg of body weight, in line with the International Society of Sports Nutrition position stand (Jäger et al., 2017). For higher body weights it's based on a healthy reference weight so the target stays realistic. Fat is set at about 25–30% of calories, within the 20–35% range recommended by EFSA. Carbohydrates fill the rest, and fibre is set at 14 g per 1,000 kcal.

These are estimates for healthy adults, not medical advice. Track your weight and energy for 2–3 weeks and adjust by 100–200 kcal if needed.