What is BMR (Basal Metabolic Rate)?
BMR (Basal Metabolic Rate) is the minimum number of calories your body needs to perform its most basic life-sustaining functions while completely at rest — like breathing, blood circulation, cell production, and maintaining organ function. Think of it as how much fuel your body burns just to "stay alive" even if you lie still all day.
This calculator goes beyond a single BMR number — it shows all three major BMR formulas side by side, a visual TDEE breakdown by activity level, an organ-by-organ energy consumption chart, and personalized tips to improve your metabolism.
How to Use This Calculator
- Select units — Metric (kg/cm) or Imperial (lbs/ft)
- Enter gender, age, height and weight
- Enter body fat % — Optional, but enables the Katch-McArdle formula for athletes
- Click Calculate BMR — See all three BMR values, full TDEE breakdown, organ energy chart and tips
BMR Formulas — All Compared
Our calculator shows results from all three major BMR formulas, so you can compare them:
Mifflin-St Jeor Equation (Most Accurate — Recommended)
Women: BMR = (10 × W) + (6.25 × H) − (5 × A) − 161
W = weight (kg) | H = height (cm) | A = age (years)
The most widely validated formula, shown to be most accurate for the general population by research published in the Journal of the American Dietetic Association. Best choice for most people.
Revised Harris-Benedict Equation (1984)
Women: BMR = (9.247 × W) + (3.098 × H) − (4.330 × A) + 447.593
Originally developed in 1919 and revised in 1984, this formula was the gold standard for decades. According to research by Roza and Shizgal, the revised version is more accurate than the original but still slightly less accurate than Mifflin-St Jeor for most people.
Katch-McArdle Formula (Best for Athletes)
Lean Body Mass = Total Weight × (1 − Body Fat Fraction)
Unlike the other formulas, Katch-McArdle uses lean body mass instead of total body weight. This makes it more accurate for lean, muscular individuals and athletes who know their body fat percentage.
BMR vs TDEE vs RMR — Key Differences
| Term | Full Form | What It Means | How Used |
|---|---|---|---|
| BMR | Basal Metabolic Rate | Calories burned at complete rest (fasted state, 12+ hrs) | Foundation for TDEE calculation |
| RMR | Resting Metabolic Rate | Calories burned at rest (not fasted, relaxed state) | Slightly higher than BMR (~10–20 cal more) |
| TDEE | Total Daily Energy Expenditure | Total calories burned in a day including all activities | Used to set daily calorie intake targets |
| TEF | Thermic Effect of Food | Calories burned digesting and processing food (~10% of TDEE) | Included in TDEE calculation |
Factors That Affect Your BMR
- Muscle Mass — More muscle = higher BMR. Muscle tissue burns ~3× more calories at rest than fat tissue. This is why strength training raises your metabolism even on rest days.
- Age — BMR naturally decreases ~1–2% per decade after age 20 due to gradual muscle loss (sarcopenia). This is why it becomes easier to gain weight with age.
- Gender — Men typically have higher BMR than women of the same height/weight due to higher muscle mass and lower body fat percentage on average.
- Body Size — Larger bodies have more tissue requiring energy, so BMR scales with height and weight.
- Genetics — Studies show up to 26% of BMR variation between individuals cannot be explained by measurable factors, suggesting a significant genetic component.
- Thyroid Function — The thyroid gland regulates metabolic rate. Hypothyroidism lowers BMR; hyperthyroidism raises it significantly. See NIDDK guidelines on thyroid function.
- Temperature — Cold environments raise BMR as your body works to maintain core temperature. BMR increases ~7% for every 1°C rise in body temperature (fever).
- Pregnancy — BMR increases significantly during pregnancy to support fetal development. According to WHO nutrition guidelines, energy needs increase by 300+ kcal/day during the second and third trimesters.
How to Increase Your BMR Naturally
Build Muscle Through Strength Training
Every pound of muscle burns approximately 6 calories per day at rest, compared to 2 calories per day for fat tissue. Adding 5 kg of lean muscle can increase your BMR by 60–80 calories per day. Over a year, this adds up significantly.
Eat Enough Protein
Protein has a thermic effect of 20–30%, meaning your body burns 20–30 calories for every 100 calories of protein consumed. This is significantly higher than carbs (5–10%) and fat (0–3%). High protein intake also helps preserve muscle mass during weight loss, preventing BMR reduction.
Avoid Extreme Calorie Restriction
Starvation diets can reduce BMR by up to 30% as the body enters "survival mode." This is called adaptive thermogenesis. Always maintain a moderate calorie deficit (300–500 cal/day) rather than extreme restriction for sustainable fat loss without metabolic damage.
Stay Consistent with Exercise
Regular aerobic exercise has a temporary BMR boost for hours after exercise (EPOC — Excess Post-exercise Oxygen Consumption). High-intensity training creates a greater EPOC effect than steady-state cardio.
Which Organs Consume the Most Energy at BMR
Your BMR calories are consumed by your vital organs, not by movement. Here is how energy is distributed at rest, based on National Academies of Medicine reference data:
| Organ/System | % of BMR | Why So Much? |
|---|---|---|
| 🧠 Brain | ~20% | Constant electrical activity and neurotransmitter production |
| 🫀 Heart & Lungs | ~19% | Never-stopping pumping and respiration |
| 🟡 Liver | ~27% | Metabolic hub — detoxification, protein synthesis, bile production |
| 🫘 Kidneys | ~10% | Constant blood filtration — 180 litres filtered daily |
| 💪 Skeletal Muscle | ~18% | Baseline muscle tone and cell maintenance |
| Other Organs | ~6% | Skin, intestines, reproductive organs, etc. |