How to use the calorie calculator
- Choose Metric (cm, kg) or Imperial (ft, in, lb). Switching converts the numbers you have already entered.
- Enter your sex, age, height and weight.
- Pick the Activity level that matches a typical week, counting both your job and your exercise.
- Read the results: the large number is your estimated maintenance intake, next to it your basal metabolic rate, and the table lists daily targets for six goals.
What the results mean
- Basal metabolic rate (BMR) – the energy your body uses in a day at complete rest: breathing, circulation, keeping warm and running your organs.
- Calories per day to keep your weight – your total daily energy expenditure (TDEE), which is BMR multiplied by an activity factor. Eating about this much should keep your weight roughly stable.
- Goal table – 250, 500 or 1,000 kcal a day below maintenance for mild, normal and fast weight loss, and 250 or 500 kcal above it for gaining. The small text gives the approximate weekly change: about 0.25, 0.5 or 1 kg (0.5, 1 or 2 lb).
- Asterisk (*) – targets under 1,500 kcal for men or 1,200 kcal for women are marked, because intakes that low are generally not advised without medical supervision.
The formula used
BMR is calculated with the Mifflin–St Jeor equation, published in 1990 and widely used by dietitians for healthy adults:
- Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
TDEE is BMR × activity factor: 1.2 sedentary, 1.375 light (exercise 1–3 days a week), 1.55 moderate (3–5 days), 1.725 active (hard exercise 6–7 days) or 1.9 very active (a physical job or training twice a day). Imperial entries are converted to centimetres and kilograms first, so both unit systems give the same answer.
Worked examples
- The starting values – a 30-year-old man, 170 cm, 65 kg: BMR = 650 + 1,062.5 − 150 + 5 = 1,567.5, shown as 1,568 kcal. With moderate activity, TDEE = 1,567.5 × 1.55 ≈ 2,430 kcal. The targets are 2,180 kcal for mild loss, 1,930 kcal for weight loss and 1,430 kcal for fast loss, which gets an asterisk because it is under 1,500.
- Activity matters most – for the same man, TDEE ranges from 1,881 kcal (sedentary) to 2,978 kcal (very active), a difference of about 1,100 kcal from a single menu choice.
- A 45-year-old woman, 160 cm, 70 kg, sedentary: BMR = 700 + 1,000 − 225 − 161 = 1,314 kcal and TDEE ≈ 1,577 kcal. A 500 kcal deficit would mean 1,077 kcal, below the 1,200 kcal guideline, so the realistic choices are the mild target of 1,327 kcal or more activity – at the light level her TDEE rises to about 1,807 kcal.
- Imperial units – a 28-year-old woman, 5 ft 5 in, 150 lb, light activity: that is 165.1 cm and 68.0 kg, giving a BMR of about 1,411 kcal and a TDEE of about 1,940 kcal.
How the weekly estimates work
The rule of thumb is that a pound of body fat stores about 3,500 kcal (roughly 7,700 kcal per kilogram), so a daily deficit of 500 kcal adds up to about 0.5 kg or 1 lb a week. It is only an approximation. Early loss includes water, and as you get lighter your energy needs fall, so progress slows: in the first example, losing 5 kg lowers the man's TDEE from about 2,430 to 2,352 kcal. Recalculate after every few kilos.
Limits of the estimate
- The equation knows your weight but not how much of it is muscle, so it can underestimate needs for very muscular people and is less reliable at very high body weights. Individual results can differ from any formula by 10% or more.
- Choosing the activity level is the biggest source of error. If you are unsure between two levels, start with the lower one.
- It is designed for adults. It is not suitable for children and teenagers, during pregnancy or breastfeeding, or for people with conditions that affect metabolism or weight.
The results are general information, not medical advice. Talk to a doctor or registered dietitian before making a big change to your diet, especially if you take medication or have a health condition.
Practical tips
- Treat the number as a starting point: eat close to it for two or three weeks, track your weight, and adjust by 100–200 kcal if it changes faster or slower than planned.
- Compare weekly averages rather than single weigh-ins; body weight can swing by a kilo or more from day to day because of water and food.
- The BMI Calculator shows a healthy weight range for your height, and the kg to lbs page converts body weights.
FAQ
Should I eat back the calories I burn exercising?
Not if your usual workouts are already counted in the activity level – that would count them twice. Only an unusual extra effort, such as a long hike, adds to the day's needs.
Why is one of my targets marked with an asterisk?
It is below 1,200 kcal (women) or 1,500 kcal (men) a day. Very-low-calorie diets make it hard to get enough protein, vitamins and minerals, so they are normally followed only under medical supervision. Choose a milder goal instead.
Why does age lower the result?
The formula subtracts 5 kcal for each year, reflecting the gradual fall in resting energy use as people get older and tend to lose muscle.