BMR Calculator
Calculate your Basal Metabolic Rate — calories your body burns at complete rest.
What is BMR?
Basal Metabolic Rate (BMR) is the energy your body needs to sustain vital functions (breathing, circulation, cell production) at complete rest. Calculated using the Mifflin-St Jeor equation — the most accurate formula for most adults.
Accuracy The Mifflin-St Jeor equation estimates BMR within ±10% for most healthy adults aged 19–78. It outperforms the older Harris-Benedict formula in most validation studies. Results are less accurate for people with very high or low body fat percentages. Clinical indirect calorimetry is the gold standard where precision is required.
Activity Multipliers
| Activity Level | Multiplier |
|---|---|
| Sedentary | × 1.2 |
| Light (1–3 days/week) | × 1.375 |
| Moderate (3–5 days/week) | × 1.55 |
| Active (6–7 days/week) | × 1.725 |
| Very Active | × 1.9 |
What to do with your result
- Multiply your BMR by your activity multiplier to get your TDEE — use our TDEE Calculator to do this automatically and get macro targets.
- To lose weight: subtract 300–500 kcal from your TDEE. A 500 kcal/day deficit produces roughly 0.5 kg of fat loss per week.
- To build muscle: add 200–300 kcal above your TDEE and ensure protein intake of 1.6–2.2 g per kg of body weight. See Protein Intake Calculator.
- If your BMR seems lower than expected, check your body fat percentage — low muscle mass (common in older adults) reduces BMR. Resistance training is the most effective way to raise resting metabolism long-term.
Frequently Asked Questions
How accurate is the BMR calculator?
The Mifflin-St Jeor equation predicts BMR within ±10% for most healthy adults. It is the most validated of the common predictive equations. Individual variation due to genetics, hormones (especially thyroid), and muscle mass means your actual BMR could differ. The Harris-Benedict formula shown for comparison tends to overestimate slightly for sedentary individuals.
What should I do with my BMR number?
BMR is the foundation of your calorie budget. Multiply it by your activity factor (see the table above) to get your TDEE — that is your maintenance calorie level. From there, create a deficit to lose fat or a surplus to gain muscle. Do not eat below your BMR for extended periods; it risks muscle loss and metabolic adaptation.
How often should I recalculate my BMR?
Recalculate whenever your weight changes by 5 kg or more, your activity level changes significantly, or every 3 months while actively dieting. As you lose weight, your BMR drops, which is why calorie targets need to be progressively adjusted to avoid weight-loss plateaus.
Is BMR different for athletes and older adults?
Yes. Athletes with high muscle mass have higher BMRs because muscle burns more calories at rest than fat. Conversely, older adults typically have lower BMRs due to age-related muscle loss (sarcopenia). For very lean or very muscular individuals, the Katch-McArdle formula — which uses lean body mass directly — provides a more accurate BMR estimate.
What is the difference between Mifflin-St Jeor and Harris-Benedict?
Both are regression equations derived from large studies. The Mifflin-St Jeor equation (1990) is generally considered more accurate for modern populations. The Harris-Benedict equation (1918, revised 1984) tends to overestimate BMR by 5–15% for overweight individuals but performs similarly for normal-weight people. Most nutrition professionals now default to Mifflin-St Jeor.
This calculator is for educational purposes only. Consult a qualified healthcare professional for medical advice.