About the BMR Calculator
Basal metabolic rate is the energy your body uses at complete rest simply to stay alive — breathing, circulation, cell repair, and brain function. It accounts for roughly 60 to 70 percent of daily energy expenditure, which makes it the foundation of any calorie target.
The formula
Mifflin-St Jeor: BMR = 10·kg + 6.25·cm − 5·age + ss is +5 for men and −161 for women. The Mifflin-St Jeor equation, published in 1990, is more accurate for modern populations than the older Harris-Benedict formula it largely replaced.
How to use this calculator
- 1Enter your Weight (kg). The field starts at
70, which you can overwrite. - 2Enter your Height (cm). The field starts at
175, which you can overwrite. - 3Enter your Age (Years). The field starts at
30, which you can overwrite. - 4Enter your Gender (1=Male, 2=Female). The field starts at
1, which you can overwrite. - 5Read the result straight away — it recalculates as you type, so there is no button to press. Use Share to copy a link that reopens the page with your exact numbers filled in.
Worked example
| Input | Value |
|---|---|
| Weight (kg) | 70 |
| Height (cm) | 175 |
| Age (Years) | 30 |
| Gender (1=Male, 2=Female) | 1 |
Result
Basal Metabolic Rate:
1649 Calories/day
Those are the values the page loads with, so you can reproduce this result yourself and then change one field at a time to see what drives the outcome.
Understanding your result
BMR is the floor, not the target. It reflects only resting expenditure, so eating at your BMR while living an ordinary life creates a substantial deficit. Total daily energy expenditure multiplies BMR by an activity factor between 1.2 for sedentary and 1.9 for very active, and that figure is what maintenance actually means.
Lean mass is the main driver, which is why the equation includes weight and why men typically have higher rates than women of the same size. It also declines with age as muscle mass falls — perhaps 1 to 2 percent per decade after 30 — and resistance training is the most effective way to slow that decline.
Things worth knowing
- Never eat below your BMR for extended periods. It risks muscle loss, nutrient deficiency, and hormonal disruption.
- The equation estimates a population average. Individual rates vary by 10 to 15 percent either side.
- Resistance training preserves lean mass, which is the single best way to protect your metabolic rate as you age.
- Prolonged severe restriction causes adaptive thermogenesis, lowering BMR beyond what weight loss alone predicts.
- Thyroid conditions can shift BMR substantially. Persistent unexplained fatigue or weight change warrants a blood test.
Frequently asked questions
What is the difference between BMR and TDEE?+
BMR is energy used at complete rest. TDEE is BMR multiplied by an activity factor, plus the energy cost of digestion, giving what you actually burn in a day. TDEE is the number to use for calorie planning.
Which BMR formula is most accurate?+
Mifflin-St Jeor is the current standard and is generally more accurate than Harris-Benedict for modern populations. Where lean body mass is known, the Katch-McArdle equation performs better still.
Can I increase my BMR?+
Modestly, mainly by building muscle, since lean tissue is more metabolically active than fat. The effect is real but gradual — a few hundred calories per day at most for significant muscle gain.
Why does BMR fall as I lose weight?+
Partly because a smaller body needs less energy, and partly through adaptive thermogenesis, where prolonged restriction reduces expenditure beyond what size alone explains. This is why weight loss plateaus.