How many calories do you need a day?
Your daily calorie need, also called total daily energy expenditure (TDEE), is the energy your body uses in 24 hours. It has two main parts: the basal metabolic rate (BMR), the energy needed to keep you alive at rest (breathing, circulation, body temperature), and the energy you use moving, working and exercising. Eat about your TDEE and your weight stays stable; eat less and you lose weight; eat more and you gain.
How the calculator works
We use the Mifflin-St Jeor equation, which studies have found to be the most accurate simple formula for estimating BMR in healthy adults:
Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161
Your BMR is then multiplied by an activity factor to estimate your TDEE:
| Activity level | Factor |
|---|---|
| Sedentary: little or no exercise | 1.2 |
| Lightly active: exercise 1–3 days a week | 1.375 |
| Moderately active: exercise 3–5 days a week | 1.55 |
| Very active: hard exercise 6–7 days a week | 1.725 |
| Extra active: physical job or training twice a day | 1.9 |
Worked example
A 30-year-old woman, 168 cm (5 ft 6 in) tall and weighing 65 kg (143 lb): BMR = 650 + 1,050 − 150 − 161 = 1,389 kcal. With light activity (× 1.375) her TDEE is about 1,910 kcal a day. A 30-year-old man, 180 cm and 80 kg, has a BMR of 1,780 kcal and needs about 2,760 kcal a day if moderately active.
Calories to lose or gain weight
A kilogram of body fat stores roughly 7,700 kcal (about 3,500 kcal per pound). That gives a simple rule of thumb:
- Eating about 500–550 kcal a day less than your TDEE leads to a loss of roughly 0.5 kg (1 lb) per week.
- A deficit of about 250–275 kcal a day gives a slower, easier-to-sustain loss of about 0.25 kg (0.5 lb) per week.
- For weight gain, for example when building muscle, a surplus of 250–500 kcal a day is a common starting point.
- Weight loss usually slows over time, because a smaller body burns fewer calories. Recalculate every few kilos.
Tips for using your number
- Treat the result as a starting estimate: track your weight for 2–4 weeks and adjust by 100–200 kcal if needed.
- Most people overestimate their activity level. If unsure, choose the lower option.
- Food quality matters too: protein, vegetables and whole foods keep you full on fewer calories.
- Very low-calorie diets can cause muscle loss and nutrient gaps and should be medically supervised.
The formula does not know your body composition: very muscular people burn more than predicted, and some medical conditions and medicines change metabolism. It is not suitable for children, teenagers, or during pregnancy or breastfeeding. To check whether your weight is in a healthy range, use the BMI calculator.
Frequently asked questions
How many calories should I eat a day?
It depends on your age, sex, size and activity. Many adult women need roughly 1,800–2,400 kcal and many adult men 2,200–3,000 kcal a day to maintain their weight. Use the calculator above for a personal estimate.
How many calories should I eat to lose weight?
Eating about 500 kcal a day less than your maintenance calories typically leads to losing about 0.5 kg (1 lb) per week. Most guidelines suggest not going below about 1,200 kcal a day for women or 1,500 for men without medical supervision.
What is the difference between BMR and TDEE?
BMR is the energy your body uses at complete rest. TDEE adds the energy you use for daily activity and exercise, so it is always higher than BMR.
How accurate is the Mifflin-St Jeor equation?
In studies it predicts resting metabolic rate within about 10% for most healthy adults. Individual results vary, so adjust based on how your weight actually changes.
What is a kilojoule?
Another unit of food energy, used on labels in Australia, New Zealand and much of Europe. 1 kcal equals 4.184 kJ.
This calculator gives a general estimate for healthy adults and is not medical or dietary advice.