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Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest just to keep vital functions running: breathing, circulation, temperature regulation, and cell repair. Understanding your BMR is the starting point for any nutrition plan, whether you want to lose, maintain, or gain weight.
This calculator uses the Mifflin-St Jeor equation, which research consistently shows is the most accurate for the general population. As noted by a study published in the Journal of the American Dietetic Association, Mifflin-St Jeor outperforms the older Harris-Benedict equation in predicting resting metabolic rate.
Mifflin-St Jeor Formula
For men: BMR = 10W + 6.25H - 5A + 5, where W is weight in kg, H is height in cm, and A is age in years.
For women: BMR = 10W + 6.25H - 5A - 161.
Multiply BMR by your activity factor to work out TDEE (Total Daily Energy Expenditure), which is the number of calories you actually need per day.
TDEE Activity Multipliers
| Activity Level | Description | Multiplier |
|---|---|---|
| Sedentary | Desk job, little exercise | BMR × 1.2 |
| Lightly active | 1-3 days/week exercise | BMR × 1.375 |
| Moderately active | 3-5 days/week exercise | BMR × 1.55 |
| Very active | Hard exercise 6-7 days/week | BMR × 1.725 |
| Extra active | Hard exercise plus physical job | BMR × 1.9 |
Given that most people overestimate their activity level, it is safer to narrow down your activity category conservatively and adjust upward if you are not losing weight at the expected rate.
How to Use BMR for Weight Management
To figure out your calorie target for weight loss, subtract 300-500 calories from your TDEE. To build up muscle, add 200-300 calories above TDEE. These moderate adjustments produce sustainable results without triggering metabolic adaptation.
With that in mind, very low calorie diets (below 1,200 for women, 1,500 for men) can reduce BMR over time as the body adapts. This is called metabolic adaptation and is one reason extremely restrictive diets often fail long-term, as documented by research in obesity reviews.
On top of that, muscle tissue burns more calories at rest than fat tissue. Resistance training builds up lean mass over time, gradually increasing BMR. Use our Calorie Deficit Calculator to set a precise daily target, and our Macro Calculator to distribute those calories across protein, carbs, and fat. The NIH guide to weight management provides additional context on energy balance.
Factors That Affect BMR
Age reduces BMR by roughly 1-2% per decade after 30, as lean muscle mass naturally declines. Gender affects BMR because men typically have more lean muscle mass. As a result, two people of identical weight and height may have significantly different BMRs depending on their body composition.
That said, this calculator uses body weight (not body fat percentage) as an input. For a more precise estimate, body composition-adjusted formulas like the Katch-McArdle equation are available when you know your lean body mass.