BMR calculator — Mifflin-St Jeor
Your Basal Metabolic Rate (BMR) is the number of calories your body burns just to stay alive at complete rest — powering breathing, circulation, brain function and cell repair, with no movement at all. Knowing it is the starting point for any calorie plan: every diet or maintenance target is built on top of your BMR. This calculator uses the Mifflin-St Jeor equation, the most accurate predictive formula for the general adult population, and works in metric or imperial units.
Why Mifflin-St Jeor and not other formulas?
Several BMR formulas exist. The Harris-Benedict equation (1919, revised 1984) was the standard for decades. The Mifflin-St Jeor equation (1990) was validated against measured resting metabolic rate in a broader population and consistently outperforms Harris-Benedict in accuracy studies, which is why most dietitians and clinical tools switched to it. The Katch-McArdle formula is more accurate if you know your lean body mass, but that requires a body-composition scan most people don’t have. For general use with weight and height, Mifflin-St Jeor is the best choice.
How it works
Imperial inputs are converted to metric first (1 lb = 0.453592 kg, 1 in = 2.54 cm). The shared base term is 10 × kg + 6.25 × cm − 5 × age, then the sex constant is added:
- Male: base + 5
- Female: base − 161
BMR does not include any activity. To estimate your full daily needs, multiply the result by an activity factor — that is exactly what the TDEE calculator does.
Worked examples
A 30-year-old man, 178 cm and 75 kg:
BMR = 10×75 + 6.25×178 − 5×30 + 5 = 750 + 1112.5 − 150 + 5 = 1,718 kcal/day
A woman with the same measurements:
BMR = 10×75 + 6.25×178 − 5×30 − 161 = 750 + 1112.5 − 150 − 161 = 1,552 kcal/day
The 166 kcal gap between those two examples reflects the sex constant only. In reality the difference is usually larger because men tend to weigh more and carry more lean mass.
How each variable moves the result
| Variable | Effect on BMR |
|---|---|
| +1 kg body weight | +10 kcal/day |
| +1 cm height | +6.25 kcal/day |
| +1 year of age | −5 kcal/day |
| Male vs female | +166 kcal/day |
From BMR to a calorie target
BMR alone is rarely your calorie goal. It is the floor — the minimum energy your body needs just to exist. Real daily need (TDEE) is BMR multiplied by an activity factor:
| Activity level | Multiplier | Example |
|---|---|---|
| Sedentary (desk job, little exercise) | 1.2 | 1,718 × 1.2 = 2,062 kcal |
| Light (1–3 days/week exercise) | 1.375 | 1,718 × 1.375 = 2,362 kcal |
| Moderate (3–5 days/week) | 1.55 | 1,718 × 1.55 = 2,663 kcal |
| Very active (6–7 days/week hard training) | 1.725 | 1,718 × 1.725 = 2,964 kcal |
To lose roughly 0.5 kg per week, subtract about 500 kcal from your TDEE. To maintain, eat at TDEE. All figures are estimates; predictive formulas can differ from measured metabolic rate by 10–15% for any individual.
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