BMR Calculator — Basal Metabolic Rate for Men and Women
Calculate your Basal Metabolic Rate (BMR) — the calories your body burns at complete rest — using the Mifflin-St Jeor equation. Foundation for any calorie plan, weight loss target or muscle-gain bulk.
All Three Formulas Compared
Total Daily Energy Needs (BMR × Activity)
What BMR Actually Means
Basal Metabolic Rate (BMR) is the calories your body would burn over 24 hours if you stayed completely at rest, lying still, after a full night's sleep, in a thermoneutral environment. It powers your heart, brain, kidneys, lungs, body temperature — all the involuntary metabolic activity. For most adults, BMR accounts for 60-70% of total daily energy expenditure (TDEE). The remaining 30-40% comes from activity, digestion (thermic effect of food), and non-exercise movement (NEAT). See Wikipedia on BMR for the physiology details.
BMR Formula for Men and Women
The Mifflin-St Jeor equation uses different constants for men and women to reflect the average difference in lean body mass:
Men: BMR = 10 × kg + 6.25 × cm − 5 × age + 5
Women: BMR = 10 × kg + 6.25 × cm − 5 × age − 161
The −161 constant for women vs +5 for men is the only sex-specific difference. The rest of the equation (weight, height, age) applies the same way. This 166-calorie gap roughly reflects the average lean-mass difference between adult men and women.
Three real scenarios
| Person | Inputs | BMR |
|---|---|---|
| Man, 35, office worker | 80 kg, 180 cm | 10×80 + 6.25×180 − 5×35 + 5 = 1,755 cal |
| Woman, 35, office worker | 65 kg, 165 cm | 10×65 + 6.25×165 − 5×35 − 161 = 1,345 cal |
| Man, 55, retired | 80 kg, 175 cm | 10×80 + 6.25×175 − 5×55 + 5 = 1,624 cal |
Notice that the 35-year-old vs 55-year-old man at the same weight burns 131 fewer calories per day at rest — that's the age effect: 5 cal/year × 20 years + 31 cal from the slightly shorter height-in-this-example.
How to Calculate Your BMR Manually
If you want to do the math without the calculator:
- Convert units if needed. Weight in kilograms (lbs ÷ 2.2046). Height in centimeters (inches × 2.54). The Mifflin-St Jeor equation requires metric.
- Apply the formula for your sex (above).
- Round to the nearest 10. The equation is ±10% accurate anyway, so the last digit is meaningless precision.
Most adults land between 1,200 and 2,000 calories per day at rest. Anything below 1,000 or above 2,500 is unusual and worth double-checking your inputs.
BMR vs TDEE: What's the Difference?
This is the most confused distinction in calorie planning. Both are calorie numbers, but they measure different things:
| BMR | TDEE | |
|---|---|---|
| Stands for | Basal Metabolic Rate | Total Daily Energy Expenditure |
| Measures | Calories at complete rest | Calories with normal life and activity |
| Used for | Baseline calculation only | Actual diet planning target |
| Typical adult value | 1,200-2,000 cal/day | 1,500-3,500 cal/day |
| Formula | Mifflin-St Jeor | BMR × activity multiplier (1.2-1.9) |
For weight management you target TDEE, not BMR. Eating at BMR while staying sedentary would still create a 200-500 calorie deficit (because real life involves some movement) — eating at BMR with normal activity creates a much bigger deficit and is usually too aggressive for sustainable fat loss.
Mifflin-St Jeor vs Harris-Benedict
Two competing equations dominate BMR calculators:
- Mifflin-St Jeor (1990) — current clinical and research standard. Validated against indirect calorimetry in modern populations. ±10% accurate. The headline number in this calculator.
- Harris-Benedict (1919, revised 1984) — older equation that overestimates BMR by 5-10% in modern populations because body composition has shifted. The Wikipedia Harris-Benedict article covers the historical equations.
- Katch-McArdle — uses lean body mass (LBM) instead of total weight: BMR = 370 + 21.6 × LBM(kg). More accurate if you know your body-fat percentage. Best for athletes and very lean or very muscular people.
Mifflin-St Jeor is the right default for almost everyone. Switch to Katch-McArdle only when you know your body fat % to within 2-3 percentage points. The calculator above shows all three side by side: enter your body fat % and the Katch-McArdle value appears next to Mifflin-St Jeor and the revised Harris-Benedict.
Two 40-year-old men, same height, same weight, different composition
| Attribute | Sedentary Office Worker | Trained Athlete |
|---|---|---|
| Height | 180 cm | 180 cm |
| Weight | 85 kg | 85 kg |
| Body fat % | 28% | 12% |
| Lean body mass | 61.2 kg | 74.8 kg |
| Mifflin-St Jeor BMR | 1,780 cal | 1,780 cal |
| Katch-McArdle BMR | 1,716 cal | 1,997 cal |
The standard Mifflin-St Jeor gives identical numbers — it doesn't see body composition. Katch-McArdle correctly captures the ~280-cal/day gap that comes from extra muscle. For athletes, fitness models, and anyone with body composition far from average, use Katch-McArdle if you know your body fat %.
From BMR to Calorie Goals
BMR alone isn't your calorie target — you move, work, exercise, digest food. Multiply BMR by an activity factor to get TDEE (Total Daily Energy Expenditure):
| Activity Level | Multiplier | Description |
|---|---|---|
| Sedentary | × 1.2 | Desk job, no exercise |
| Lightly active | × 1.375 | Light exercise 1-3 days/week |
| Moderately active | × 1.55 | Moderate exercise 3-5 days/week |
| Very active | × 1.725 | Hard exercise 6-7 days/week |
| Athlete / physical job | × 1.9 | Twice/day training or manual labor |
For weight management: 500 calories below TDEE ≈ 1 lb/week loss; 500 above ≈ 1 lb/week gain; at TDEE = maintenance. For more on this, see our calorie calculator and the dedicated TDEE calculator.
Why BMR Drops With Age (and What to Do)
Lean muscle mass declines by roughly 1% per year after age 30 in inactive adults — a process called sarcopenia. Muscle is metabolically active; fat is mostly inert. Less muscle = lower BMR. Combined with hormonal shifts (testosterone in men, estrogen in women), BMR typically drops 1-2% per decade after 30 without intervention.
The single best counter: resistance training. Adults who lift 2-3 times per week from age 30 onward maintain 80-90% of peak muscle mass into their 60s. The CDC's physical activity guidelines recommend muscle-strengthening activity on 2+ days per week for exactly this reason.
Frequently Asked Questions
How do I calculate BMR for men?
Mifflin-St Jeor for men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5. Example: 80 kg, 180 cm, 35 years → 800 + 1125 − 175 + 5 = 1,755 cal/day.
How do I calculate BMR for women?
Mifflin-St Jeor for women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161. Example: 65 kg, 165 cm, 35 years → 650 + 1031 − 175 − 161 = 1,345 cal/day. The −161 (vs +5 for men) reflects average lean-mass differences.
What is the difference between BMR and TDEE?
BMR is calories at complete rest. TDEE is BMR plus activity, digestion and movement. TDEE = BMR × activity multiplier (1.2 sedentary to 1.9 athlete). For weight management you target TDEE, not BMR.
How to calculate BMR by hand?
Convert weight to kg (lbs ÷ 2.2046) and height to cm (inches × 2.54). Apply the Mifflin-St Jeor formula for your sex. Round to nearest 10. Most adults land 1,200-2,000 cal/day.
Which is more accurate, Mifflin-St Jeor or Harris-Benedict?
Mifflin-St Jeor (1990). Harris-Benedict (1919) overestimates BMR by 5-10% in modern populations because body composition has shifted. Mifflin-St Jeor is the current clinical and research standard.
How accurate is the Mifflin-St Jeor equation?
±10% for typical adults. People at extremes (very lean, very obese, athletes, elderly) get less accurate estimates. The gold standard is indirect calorimetry in a metabolic lab.
Why does BMR drop with age?
Muscle mass decline (sarcopenia), hormonal shifts, and reduced cellular metabolic rate. Resistance training and adequate protein (1.2-1.6 g/kg body weight after age 50) are the strongest counter-measures.
Can I increase my BMR?
Yes — build muscle. Every pound of muscle burns 6-10 cal/day at rest. Building 10 lb of muscle over a year could raise BMR by 60-100 cal/day. Supplements and "metabolism-boosting" drinks have negligible effect.
Does eating frequently boost BMR?
No — the "6 small meals stoke the metabolism" claim isn't supported by research. Studies show no significant TDEE difference between 3 and 6 meals/day at the same total calories.
Why does my smartwatch show a different number?
Smartwatches estimate using heart-rate and proprietary algorithms that include activity. They typically report TDEE, not BMR, and are often off by 15-25%. Use them for trend tracking, not absolute numbers.
How does the Katch-McArdle formula work?
Katch-McArdle calculates BMR from lean body mass instead of total weight: BMR = 370 + 21.6 × LBM(kg), where LBM = weight × (1 − body fat % ÷ 100). Example: 85 kg at 15% body fat → LBM = 72.25 kg → BMR = 370 + 1,561 = 1,931 cal/day. Enter your body fat % in the calculator above to see it next to the other two formulas.
Sources
- Mifflin MD, St Jeor ST, et al. "A new predictive equation for resting energy expenditure in healthy individuals." Am J Clin Nutr, 1990 — the original paper behind the default formula.
- Roza AM, Shizgal HM. "The Harris Benedict equation reevaluated." Am J Clin Nutr, 1984 — the revised Harris-Benedict constants this calculator uses.
- Wikipedia: Basal metabolic rate — physiology background and formula overview.