How to use the calorie calculator
Enter your age, sex, weight, height and how active you are. The calculator estimates your basal metabolic rate (BMR), the calories your body burns at rest, then multiplies it by an activity factor to get your total daily energy expenditure (TDEE): the calories that keep your weight steady. It also shows targets for gradual weight loss or gain, in both kcal and kJ.
Formulas used
Mifflin-St Jeor BMR (men) = 10 × kg + 6.25 × cm − 5 × age + 5
Mifflin-St Jeor BMR (women) = 10 × kg + 6.25 × cm − 5 × age − 161
Katch-McArdle BMR = 370 + 21.6 × lean body mass (kg)
TDEE = BMR × activity factor
Mifflin-St Jeor is the formula most dietitians use for healthy adults. If you enter a body fat percentage, the calculator uses Katch-McArdle instead, which is based on lean mass.
Worked example
A 30-year-old man, 80 kg, 180 cm, moderately active (× 1.55):
BMR = 800 + 1,125 − 150 + 5 = 1,780 kcal. TDEE = 1,780 × 1.55 = 2,759 kcal a day (11,544 kJ). Eating about 500 kcal a day less, around 2,259 kcal, would mean losing roughly 0.5 kg a week.
Activity factors
| Activity level | Factor |
|---|---|
| Sedentary: desk job, 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 plus training | 1.9 |
Losing or gaining weight safely
A deficit of about 500 kcal a day leads to roughly 0.5 kg (1 lb) of weight loss a week, the pace the NHS and most health services recommend. The calculator won't suggest targets below about 1,200 kcal a day for women or 1,500 for men, because going lower without medical supervision makes it hard to get enough nutrients.
Check where your weight sits with the BMI calculator.
Frequently asked questions
What's the difference between BMR and TDEE?
BMR is what you burn at complete rest. TDEE adds everything you do in a day, from walking to workouts. TDEE is the number to eat to maintain your weight.
Why does the calculator show kJ?
Food labels in Australia and New Zealand list energy in kilojoules. 1 kcal = 4.184 kJ.
How accurate is this?
For most adults, Mifflin-St Jeor is within about 10% of measured BMR. Track your weight for 2 to 3 weeks and adjust if it moves when you expect it to stay steady.
Sources
Formulas checked 29 October 2026. How we test our calculators. This calculator gives general estimates for adults and is not medical advice. Talk to a doctor or dietitian about your own health.