How to Use This Calculator
- Select your measurement system: Choose Metric (kilograms and centimeters) or US Units (pounds, feet, and inches).
- Enter your vitals: Select your biological sex, age, standing barefoot height, and current morning body weight.
- Pick your activity level: Choose the option that best mirrors your weekly physical routine, from desk-bound sedentary to heavy physical training.
- Review your targets: See your baseline BMR, your daily maintenance calories (TDEE), and exact deficit numbers for safe weight loss or muscle building.
The Formula
Your Basal Metabolic Rate represents the minimum calorie floor required to maintain vital organ function, breathing, cellular repair, and temperature control while lying completely still. This calculator uses the Mifflin-St Jeor Equation, recognized in clinical medicine as the most reliable predictive formula for modern adults:
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
To convert resting BMR into daily maintenance calories (TDEE), we multiply by your physical activity factor (PAL):
- Sedentary (1.2): Desk work, little walking, no planned workouts.
- Lightly Active (1.375): Light jogging, yoga, or lifting 1 to 3 days per week.
- Moderately Active (1.55): Moderate resistance training or cardio 3 to 5 days per week.
- Very Active (1.725): Rigorous training or intense sports 6 to 7 days per week.
- Extra Active (1.9): Daily two-a-day athletic sessions or arduous manual labor.
Revised Harris-Benedict & Katch-McArdle Formulas
We also calculate the 1984 Revised Harris-Benedict baseline side-by-side for comparison. If you provide an optional body fat percentage, the tool activates the Katch-McArdle Formula (BMR = 370 + 21.6 × lean mass in kg). Because lean muscle burns calories while fat tissue is largely passive, Katch-McArdle provides elite accuracy for lean lifters and athletes.
I work a regular desk job, so I spend seven to eight hours a day sitting in front of a monitor. When I first ran my numbers through a metabolic formula a couple of years back, I assumed a sedentary day burned almost nothing. Seeing that my body burns over 1,600 calories just staying alive—pumping blood and keeping organs running without me lifting a finger—completely shifted how I looked at daily energy balance. Your baseline metabolism does most of the heavy lifting.
Example
Scenario: A 30-year-old male who stands 175 cm tall, weighs 70 kg, and exercises moderately 4 days per week (activity multiplier 1.55).
- Step 1 (Base BMR):
(10 × 70) + (6.25 × 175) − (5 × 30) + 5
= 700 + 1093.75 − 150 + 5 = 1,648.75 ≈ 1,649 kcal/day - Step 2 (Maintenance TDEE):
1,648.75 × 1.55 = 2,555.56 ≈ 2,556 kcal/day - Step 3 (Fat Loss Deficit):
To lose 0.5 kg (roughly 1 lb) per week, he subtracts 500 calories:2,556 − 500 = 2,056 kcal/day. - Step 4 (Lean Muscle Surplus):
To gain weight gradually while lifting, he adds a moderate surplus:2,556 + 500 = 3,056 kcal/day.
Without ever stepping into a costly metabolic testing lab, he knows exactly what calorie window will move the scale in his chosen direction.
Frequently Asked Questions
What is the difference between BMR and TDEE?
Basal Metabolic Rate (BMR) is what your body burns just staying alive in bed with your eyes closed. Total Daily Energy Expenditure (TDEE) takes that baseline and adds walking, working, exercising, and digesting meals throughout your waking hours.
Why does BMR decrease as we get older?
Hormonal changes and natural aging reduce muscle tissue unless you deliberately train to preserve it. Since lean muscle consumes roughly three times more energy at rest than fat tissue, a drop in muscle mass lowers your baseline daily burn.
Which formula is most accurate for calculating BMR?
For most people, the Mifflin-St Jeor equation used here is the most dependable option. If you have had an accurate body scan and know your exact body fat percentage, the Katch-McArdle formula will tailor the result directly to your lean mass.
Should you ever eat fewer calories than your BMR?
Eating beneath your BMR is usually a bad strategy. Your vital organs need that minimum energy to repair tissue and keep your hormone profile healthy; severe deficits cause brain fog, muscle loss, and severe rebound overeating later.
How does building muscle affect BMR?
Muscle is active tissue that demands oxygen and glucose even while you rest. Adding 3 to 5 kilograms of solid muscle increases your daily calorie burn permanently, making it much easier to stay lean without starving yourself.
Every time I tried an aggressive crash diet in the past, cutting calories down to some ridiculous 1,200-calorie limit, I quit within ten days. I was exhausted, irritable, and ended up eating everything in sight. What actually works is a modest 300 to 400 calorie deficit below maintenance. It feels slow in week one, but you keep your energy, you sleep well, and you can stick with it for months without feeling miserable.