This calculator estimates how many calories your body uses in a day, known as total daily energy expenditure (TDEE). It uses the Mifflin-St Jeor equation for your resting rate, multiplies it by your activity level, and suggests gradual targets for weight loss or gain that never go below safe minimums.
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How to use it
- Enter your sex, age, height and weight.
- Choose the activity level that matches a typical week, not your best week.
- Use the result as a starting point and adjust after 2–3 weeks based on how your weight actually changes.
How it’s calculated
- Resting rate (BMR): 10 × weight in kg + 6.25 × height in cm − 5 × age, then +5 for men or −161 for women.
- TDEE: BMR × activity factor: 1.2 (mostly sitting), 1.375 (light), 1.55 (moderate), 1.725 (hard), 1.9 (physical job plus training).
- Gradual loss: about 500 kcal a day below TDEE, roughly 0.5 kg a week.
Worked examples
| Person | BMR | Activity | Maintenance |
|---|---|---|---|
| Woman, 32, 165 cm, 68 kg | 1,390 | Light (×1.375) | about 1,912 kcal |
| Man, 40, 180 cm, 85 kg | 1,780 | Moderate (×1.55) | about 2,759 kcal |
The NHS rule of thumb is around 2,000 kcal a day for women and 2,500 for men, which sits close to these figures for moderately active adults.
Safe limits
The calculator never suggests fewer than 1,200 kcal a day for women or 1,500 for men. Very low-calorie diets (800 kcal or less) should only be followed with medical supervision. If you’re pregnant, breastfeeding, under 18, have a medical condition or a history of disordered eating, speak to a GP or registered dietitian before changing what you eat.
Frequently asked questions
How many calories should I eat a day?
It depends on your size, age, sex and activity. This calculator estimates it; most adults fall between about 1,800 and 3,000 kcal a day.
How accurate is the Mifflin-St Jeor equation?
It’s one of the more accurate formulas for most adults, but individuals can differ by around 10%. Track your weight for a few weeks and adjust.
How fast is it safe to lose weight?
A gradual loss of about 0.5 to 1 kg a week is generally recommended. Faster loss is harder to sustain and can lose muscle.
Sources
- NHS: Understanding calories
- Mifflin MD et al. (1990), A new predictive equation for resting energy expenditure
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