How to use the calorie calculator
- Choose Metric (cm, kg) or Imperial (ft, st, lb).
- Pick your Sex and enter your Age, Height and Weight.
- Choose the Activity level that matches a typical week, not your best week.
- Leave the Formula on Mifflin-St Jeor, or choose Katch-McArdle and enter your Body fat percentage if you know it from a reliable measurement.
- Read your BMR, your maintenance calories (TDEE) and the daily targets for losing, keeping or gaining weight.
BMR, TDEE and maintenance calories
BMR (basal metabolic rate) is the energy your body uses at complete rest to keep you alive: breathing, circulation, temperature and organ function. For most people it is the largest part of the day's energy use. TDEE (total daily energy expenditure) adds everything else: daily movement, exercise and digesting food. If you eat about your TDEE, your weight tends to stay the same, which is why it is also called your maintenance calories.
The calculator estimates BMR with one of two formulas:
- Mifflin-St Jeor (default), published in 1990 and widely recommended for healthy adults: men = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5; women = the same but − 161 instead of + 5. Example: a 30-year-old man, 180 cm and 80 kg, has a BMR of 800 + 1,125 − 150 + 5 = 1,780 kcal.
- Katch-McArdle: 370 + 21.6 × lean body mass (kg), where lean mass = weight × (1 − body fat %). It ignores age and sex but needs an accurate body fat figure. With 80 kg and 20% body fat: 370 + 21.6 × 64 = 1,752 kcal.
BMR is then multiplied by an activity factor to give TDEE:
| Activity level | Typical week | Multiplier |
|---|---|---|
| Sedentary | Desk job, little or no exercise | 1.2 |
| Lightly active | Light exercise or sport 1 to 3 days a week | 1.375 |
| Moderately active | Moderate exercise 3 to 5 days a week | 1.55 |
| Very active | Hard exercise 6 to 7 days a week | 1.725 |
| Extremely active | Hard daily training, or a physical job plus exercise | 1.9 |
For the example man above, moderately active: 1,780 × 1.55 = 2,759 kcal a day. Most people overestimate how active they are, so if you are unsure, pick the lower level.
Calories to lose or gain weight
A common rule of thumb is that a kilogram of body fat stores about 7,700 kcal (about 3,500 kcal per pound). Eating 550 kcal a day below your TDEE would therefore lose roughly 0.5 kg a week, and 1,100 kcal a day roughly 1 kg. In reality weight loss slows over time as your body gets lighter and adapts, so treat the targets as a starting point and adjust them after a few weeks based on what actually happens. The NHS suggests aiming to lose 0.5 to 1 kg (1 to 2 lb) a week.
The calculator will not show a target below a sensible minimum: 1,500 kcal a day for men and 1,200 kcal a day for women, figures commonly cited as the lowest intake to follow without medical supervision. Very low-calorie diets (800 kcal a day or less) should only be followed with a doctor's supervision. If the safe options look slow, combine a moderate deficit with more activity rather than eating less.
How accurate is it?
Every formula is an average. Studies comparing predicted and measured resting energy use found Mifflin-St Jeor to be the most reliable of the common equations, yet individuals can still be 10% or more above or below the estimate because of genetics, muscle mass, hormones and medication. Use the result as a first estimate, track your weight for two to four weeks, then adjust your intake by 100 to 200 kcal a day if needed.
This tool is for adults. It is not suitable during pregnancy or breastfeeding, for under-18s, or if you have or have had an eating disorder; ask a doctor, midwife or registered dietitian instead.
Check where your weight sits for your height with the BMI calculator, and read what BMI means and its limits. To switch units, use the kg to lbs converter. More tools are on the health tools page.
Privacy: the calculation runs in your browser and your details are not sent anywhere or stored. Only your choice of metric or imperial units is remembered in this browser.
Frequently asked questions
How many calories should I eat a day?
Roughly your TDEE to keep your weight steady. As a general guide the NHS uses about 2,500 kcal a day for men and 2,000 kcal for women, but your own figure depends on your size, age and activity, which is what this calculator estimates.
What is TDEE?
Total daily energy expenditure: the calories you burn in a day, including your resting metabolism (BMR), everyday movement, exercise and digestion. It is the same as your maintenance calories.
How do I calculate a calorie deficit?
Subtract a daily amount from your TDEE. About 550 kcal a day below maintenance gives roughly 0.5 kg (1.1 lb) of weight loss a week; 500 kcal a day gives about 1 lb a week. Do not go below about 1,200 kcal (women) or 1,500 kcal (men) a day without medical supervision.
What is the difference between BMR and TDEE?
BMR is the energy used at complete rest; TDEE is BMR plus everything you do in a day. TDEE is always higher: from 1.2 times BMR for a sedentary person to about 1.9 times for someone very active.
Which formula is the most accurate?
For most healthy adults, Mifflin-St Jeor. Katch-McArdle can be better for very lean or muscular people, but only if you know your body fat percentage from a reliable measurement.
Why am I not losing weight on my calorie target?
The estimate may be too high for you, portions are easy to underestimate, and weight naturally varies by a kilogram or more from day to day. Compare weekly averages over three or four weeks, then lower your intake slightly or add activity. If nothing changes, talk to your doctor.
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