Accurate calculation of your basal metabolic rate (BMR) and daily calorie needs (TDEE) using the Mifflin-St Jeor equation
Calories needed at complete rest
Total calories to maintain your weight
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These are standard ratios — adjust them to suit your needs
| Goal | Daily Calories | Weight Change |
|---|---|---|
| Fast weight loss | -- | -1 kg/week |
| Moderate weight loss | -- | -0.5 kg/week |
| Maintain current weight | -- | 0 kg/week |
| Slow weight gain | -- | +0.25 kg/week |
| Weight gain | -- | +0.5 kg/week |
Keep in mind: these figures are a scientific estimate. For the best results, track your weight weekly and adjust your calories as needed. For healthy weight loss, aim to lose no more than 1 kg per week.
BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest to carry out vital functions — breathing, circulation, temperature regulation and cellular activity. Put another way, it is what your body needs over 24 hours if you were awake but doing nothing at all. BMR accounts for roughly 60-75% of your total daily calorie expenditure.
TDEE (Total Daily Energy Expenditure) is the total number of calories your body burns across a full day, with all activity accounted for. TDEE is your BMR plus the calories burned through daily activity, exercise and even digesting food (the thermic effect of food, or TEF). To maintain your weight, eat at your TDEE; eat below it to lose weight and above it to gain.
The Mifflin-St Jeor equation was published in 1990 and has since been recognised as the most accurate formula for estimating BMR. Research has shown it is more accurate than Harris-Benedict and can estimate BMR to within ±10%. The formula is:
Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
The formula is simple, needs only basic information, and is accurate enough for most people. The 166-unit difference between men and women reflects metabolic and body-composition differences between the sexes.
Harris-Benedict is one of the oldest BMR formulas, introduced in 1919 and revised in 1984. Although still widely used, studies have found it tends to overestimate BMR slightly compared with Mifflin-St Jeor. The revised formula is:
Men: BMR = 66.5 + (13.75 × weight) + (5.003 × height) − (6.75 × age)
Women: BMR = 655.1 + (9.563 × weight) + (1.850 × height) − (4.676 × age)
Katch-McArdle is the only formula that uses lean body mass rather than total weight. It is considerably more accurate for people who know their body fat percentage, particularly athletes and bodybuilders. A single formula covers both sexes:
Everyone: BMR = 370 + (21.6 × lean body mass in kg)
Lean body mass = weight × (1 − body fat percentage ÷ 100)
Once you have your BMR, multiply it by the factor matching your activity level to get your TDEE. These multipliers come from published research:
Worth noting: most people overestimate their activity level. Be honest, and pick the lower option when you are unsure. Don't over-count everyday movement such as walking around the house or standing, either.
To lose weight you need a calorie deficit — eating below your TDEE. One kilogram of fat is roughly 7,700 calories, which gives you:
Careful: deficits beyond 1,000 calories are not advisable — they can cost you muscle, lower your metabolic rate and leave you short on nutrients. And never eat below your BMR.
Healthy weight gain (building muscle) requires a calorie surplus. To add muscle with as little fat gain as possible:
To hold your current weight, your intake should sit at roughly your TDEE. It will naturally fluctuate day to day, but over the long run the average should match your TDEE.
Total calories aren't the whole picture — how you split your macros matters too. Each macronutrient plays its own role in the body:
Protein is essential for building and repairing muscle, supporting immune function and keeping you full. Aim for 25-35% of your daily calories from protein, which works out to 1.6-2.2 g per kilogram of body weight. For people losing weight or building muscle, that can go as high as 2.5 g. Protein has the highest thermic effect of the three macros — 20-30% of its calories are spent on digestion.
Carbohydrates are your body's main energy source, especially for hard training and brain function. Aim for 35-50% of daily calories from carbs; for people training intensely that can rise to 50-60%. Favour complex carbohydrates such as brown rice, oats, sweet potato and vegetables over simple carbs.
Healthy fats are essential for hormone production, absorbing fat-soluble vitamins (A, D, E, K) and brain health. Aim for 20-35% of daily calories from healthy fats — omega-3s, olive oil, avocado and nuts. At least 15-20% of your calories should come from fat to keep hormone function normal.
BMR (Basal Metabolic Rate) and RMR (Resting Metabolic Rate) are often used interchangeably, but there are small differences. BMR is measured under tightly controlled conditions: after eight hours of sleep, at complete rest, in a neutral environment and at least 12 hours after the last meal. RMR has looser conditions and typically comes out 10-20% higher than BMR. In practice, the formulas in this calculator estimate RMR, which is fine for everyday use.
When you stay in a calorie deficit for a long stretch, your body responds by lowering its metabolic rate to conserve energy. This is called metabolic adaptation, and it can stall weight loss. To avoid it:
One last thing: this calculator is an excellent starting point, but every body is different. After 2-3 weeks, adjust your calories based on your actual progress. For the fullest picture, use the body fat percentage calculator as well, to confirm the weight you're losing is fat rather than muscle.
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