How to use the calorie calculator
- Enter your sex, age, height and weight.
- Choose your activity level honestly. Most people with desk jobs who train a few times a week are "light" or "moderate".
- Read your maintenance calories (the energy you burn in a typical day) and the targets to lose or gain weight.
How it is calculated
First the calculator estimates your basal metabolic rate (BMR), the energy your body uses at complete rest, with the Mifflin–St Jeor equation. Studies comparing equations found it to be the most accurate for most adults.
Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
Then BMR is multiplied by an activity factor (1.2 for sedentary up to 1.9 for very active) to get your total daily energy expenditure (TDEE).
Example
A 30-year-old woman, 165 cm and 68 kg: BMR = 680 + 1,031 − 150 − 161 = 1,400 kcal. With light activity (× 1.375) her maintenance is about 1,930 kcal a day. Eating about 500 kcal less, roughly 1,430 kcal, would lead to a loss of around 0.5 kg a week.
How fast is safe to lose weight?
Health services such as the NHS and CDC suggest aiming for about 0.5 to 1 kg (1 to 2 lb) a week. A deficit of about 500 kcal a day gives roughly 0.5 kg a week; this is an approximation, because the body adapts as you lose weight. Diets below about 1,200 kcal (women) or 1,500 kcal (men) are hard to make nutritious and should be supervised by a professional, which is why the calculator marks them with ⚠.
Why protein matters
The basic recommended intake for adults is about 0.8 g of protein per kg of body weight a day. Research suggests that active people and those losing weight benefit from more, often 1.2 to 1.6 g/kg, to help keep muscle. People with kidney disease should follow their doctor's advice on protein.
See our step-by-step guide how to lose weight safely.
Frequently asked questions
How accurate is the result?
Equations predict BMR within about 10% for most people. Use the number as a starting point, track your weight for 2–3 weeks and adjust by 100–200 kcal if needed.
Should I eat back calories from exercise?
Your activity level already includes your usual exercise. Fitness trackers often overestimate calories burned.
Can I use it during pregnancy?
No. Energy needs change during pregnancy and breastfeeding; ask your midwife, doctor or a dietitian.
Is my data stored?
No. Everything is calculated in your browser.
Sources: Mifflin MD, St Jeor ST et al., American Journal of Clinical Nutrition, 1990; Frankenfield D et al., Journal of the American Dietetic Association, 2005; NHS, "Losing weight"; CDC, "Losing weight"; National Academies, Dietary Reference Intakes for protein.
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Last reviewed: 2026-11-09. These tools give general information, not medical advice. Talk to a doctor about your health. See our medical disclaimer.