How does the calorie calculator work?
Our calorie calculator uses the Mifflin-St Jeor equation — the formula recommended by most nutritional scientists as the most accurate method for calculating basal metabolic rate (BMR). It calculates your BMR using this formula:
- Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 5
- Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
The BMR is then multiplied by an activity factor (PAL value) to obtain your total daily energy expenditure (TDEE). Based on your goal, we add or subtract calories to give you a practical daily target.
What is the basal metabolic rate?
Your basal metabolic rate (BMR) is the energy your body needs at complete rest — for breathing, heart function, cell repair and maintaining body temperature. It typically accounts for 60–75% of your total daily energy expenditure. The BMR is influenced primarily by muscle mass, age, gender and body size. More muscle means a higher BMR, which is why strength training is valuable even for weight loss — it raises your baseline calorie burn.
How many calories for weight loss?
For weight loss, you need a calorie deficit — consuming less energy than you burn. We recommend a moderate deficit of 300–500 kcal below your TDEE. This allows steady fat loss of approximately 0.4–0.5 kg per week while preserving muscle mass. A deficit larger than 1,000 kcal is counterproductive: it promotes muscle loss, slows your metabolism, increases hunger and makes the diet harder to sustain. Slow and steady wins — and keeps the weight off long-term.
How many calories for muscle gain?
For muscle gain, you need a calorie surplus — consuming more energy than you burn. We recommend a moderate surplus of 200–400 kcal above your TDEE. Combined with progressive strength training and adequate protein (1.6–2.0 g per kg bodyweight), this supports lean mass gains of approximately 0.5–1 kg per month. A larger surplus leads primarily to fat gain, not faster muscle growth — your body can only build muscle at a limited rate.
Calorie needs for women vs. men
Men typically need 2,000–3,000 kcal per day, women 1,600–2,400 kcal — but these are rough averages. The difference comes from men generally having more muscle mass (which burns more energy at rest) and larger body frames. However, individual variation is huge: an active woman who trains 5 times per week will need significantly more calories than a sedentary man. That's why a personalised calculation based on your data is far more useful than generic guidelines.
Activity levels explained
The activity factor accounts for all physical activity throughout your day — not just exercise, but also your job, daily movement and household tasks:
- Sedentary (factor 1.2): Office job, minimal movement, no regular exercise.
- Lightly active (factor 1.375): Light exercise 1–2 times per week or an active commute.
- Moderately active (factor 1.55): 3–5 workouts per week. The most common level for regular gym-goers.
- Very active (factor 1.725): Daily intense exercise or a physically demanding job combined with regular training.
- Extremely active (factor 1.9): Physical labour combined with daily intense training. Typical for professional athletes or tradespeople who also train.
Next step: from calorie number to nutrition plan
A calorie calculator gives you a solid starting point, but real results come from consistency and a structured plan. Fytrr uses AI to build a personalised nutrition plan based on your calorie target, dietary preferences and fitness goals. Every meal is calculated, every macro is accounted for — and you can swap meals anytime. Try it free for 7 days.
