Whether you want to lose weight, build muscle or simply eat well, it helps to know roughly how much energy your body uses each day. Calories are a unit of energy, and your daily needs depend on your size, age, sex and activity. This guide explains how the estimate works, step by step, and how to use it responsibly.
Step 1: your basal metabolic rate (BMR)
BMR is the energy your body burns at complete rest to keep you alive: breathing, circulation, temperature control and cell repair. It represents the largest share of daily calorie use for most people. A widely used estimate is the Mifflin-St Jeor equation:
- Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
Example: A 30-year-old man, 175 cm tall and weighing 75 kg: 10 × 75 = 750; 6.25 × 175 = 1,093.75; 5 × 30 = 150. So BMR = 750 + 1,093.75 − 150 + 5 = 1,698.75 calories per day.
Step 2: add your activity level
To find your total daily energy expenditure (TDEE), multiply BMR by an activity factor:
- 1.2: sedentary (desk job, little exercise)
- 1.375: lightly active (light exercise 1–3 days a week)
- 1.55: moderately active (exercise 3–5 days a week)
- 1.725: very active (hard exercise 6–7 days a week)
- 1.9: extra active (physical job plus training)
Continuing the example with moderate activity: 1,698.75 × 1.55 ≈ 2,633 calories per day to maintain weight.
Be honest when choosing your level. Most people overestimate how active they are, which leads to an inflated target. If unsure, choose the lower level and adjust based on results.
Step 3: adjust for your goal
About 7,700 calories are roughly equal to 1 kg of body fat. That gives a simple rule of thumb:
- To lose about 0.5 kg per week: eat about 500 calories below maintenance, which here is about 2,133 per day.
- To gain about 0.5 kg per week: eat about 500 calories above maintenance.
The body adapts, so real results vary, and weight fluctuates daily because of water, salt and digestion. Judge progress over two to four weeks, not day to day.
Safe limits
- Avoid very low-calorie diets unless supervised by a doctor. Eating too little can cause fatigue, nutrient deficiencies and muscle loss.
- A common guideline is to avoid going below roughly 1,200 calories for women or 1,500 for men without medical guidance.
- A gradual loss of 0.25 to 1 kg per week is considered a sustainable pace for most adults.
Calories are not the whole story
- Protein keeps you fuller and helps preserve muscle when you lose weight.
- Fibre from vegetables, fruit, legumes and whole grains supports digestion and fullness.
- Sleep and stress affect appetite hormones and cravings.
- Strength training helps maintain or build muscle, which supports your metabolism.
- Food quality matters for health regardless of calorie count.
Limits of calculators
These equations give an estimate for typical healthy adults. Individual metabolism can differ by several hundred calories. Pregnancy, breastfeeding, certain medical conditions, medications and very high or low body fat can change needs significantly. This article does not provide medical advice. If you have a health condition, a history of disordered eating, or are planning significant changes, speak to a doctor or registered dietitian first.
Calculate yours
Use our Calorie Calculator to enter your sex, age, height, weight and activity level and instantly see your BMR, maintenance calories and rough targets for losing or gaining weight.