About the BMR & Calorie Calculator
This calculator estimates your basal metabolic rate, the calories your body burns at complete rest, then scales that figure by your activity level to estimate your total daily energy expenditure, commonly called maintenance calories. It uses the Mifflin-St Jeor equation, the formula most dietitians currently recommend as the most accurate widely available estimate from just age, height, weight and sex.
How to use the BMR & Calorie Calculator
- 1
Select your sex, since the formula uses a different constant for each.
- 2
Enter your age, height in centimetres and weight in kilograms.
- 3
Choose the activity level that best matches your typical week, from sedentary to extremely active.
- 4
Read your BMR and maintenance calories, plus the suggested targets for losing, maintaining or gaining weight.
What people use it for
Setting a calorie target for weight loss
Use the suggested deficit figure as a starting point for a sustainable, moderate weight loss plan rather than guessing at a calorie target.
Working out calories needed to maintain weight
Check your maintenance figure before a period where you specifically want to hold weight steady, such as during a training block.
Planning a calorie surplus for muscle gain
Use the suggested surplus figure as a starting point for lean weight gain, adjusting based on how your actual weight trends over a few weeks.
The Mifflin-St Jeor equation
For men, BMR equals 10 times weight in kilograms, plus 6.25 times height in centimetres, minus 5 times age, plus 5. For women, the same formula is used but ends by subtracting 161 instead of adding 5. Published in 1990 and validated repeatedly since, it has been shown to predict measured resting energy expenditure more accurately on average than the older Harris-Benedict equation still found on many older calculators, which is why current dietetic guidance favours it.
Why the calorie targets use a 500 kcal margin
A kilogram of body fat represents roughly 7,700 kilocalories of stored energy, so a sustained daily deficit or surplus of 500 kcal works out to a weekly total close to 3,500 kcal, which translates to approximately half a kilogram of change per week. This is a moderate, widely recommended pace — steep deficits well beyond this are harder to sustain and risk more muscle loss alongside fat loss, while very large surpluses add fat faster than the body can build muscle.
Tips
- Re-check your numbers every few weeks as your weight changes, since BMR shifts with body weight.
- Activity level should reflect your typical week, not your best or worst day — most people overestimate this by one category.
- Treat the calorie targets as a starting point and adjust based on your actual weight trend over two to three weeks, not a single day's reading.