BMR Calculator

You will lose weight eating below your TDEE, but eating at or just above BMR is often too aggressive and unsustainable. This creates a massive deficit (potentially 500-1,500+ calories) which causes muscle loss, extreme hunger, fatigue, and metabolic adaptation. Healthy weight loss is 0.5-1 kg per week, achieved with a 500-1,000 calorie deficit below TDEE (not BMR). For example, if TDEE is 2,500 cal, eat 1,500-2,000 cal/day, not 1,200 cal. This approach preserves muscle, maintains energy, and is sustainable.

The Mifflin-St Jeor equation is one of the most accurate BMR prediction formulas, typically within ±10-20% of actual metabolic rate for most people. However, accuracy varies based on body composition, genetics, metabolism, hormones, medications, and health conditions. Muscular individuals may have higher BMR; sedentary people lower. The formula is a starting point—track real results and adjust calories up or down based on actual weight change. If calculated TDEE is 2,500 cal but you're not losing weight after 2-4 weeks, adjust to 2,400 cal and monitor again.

Yes significantly. BMR decreases ~2% per decade after age 20 due to natural muscle loss. Women have ~5-10% lower BMR than men (formula accounts for this). Muscle is metabolically active; muscle gain increases BMR, muscle loss decreases it. Hormonal factors (thyroid, cortisol) affect metabolism. Extreme dieting can lower BMR temporarily (metabolic adaptation). Building muscle through strength training is one of the best ways to increase BMR long-term. This calculator estimates BMR; if you suspect thyroid or metabolic issues, consult a healthcare provider.

Track results for 2-4 weeks before adjusting. If losing weight slower than expected, reduce calories by 100-150 per day. If no loss, reduce by 200-300. If gaining when you meant to lose, you're in a surplus—reduce by 300-500 cal. Conversely, if trying to gain but maintaining, add 200-300 cal. Changes should be gradual; aggressive cuts cause muscle loss and metabolic slowdown. Also verify you're tracking accurately—measure portions, use a scale, log everything. Sometimes perceived plateaus are just natural fluctuations (water weight, hormones). Patience and consistency matter more than perfection.

Thyroid disorders, PCOS, diabetes, hormonal imbalances, and medications can significantly affect metabolism. Someone with hypothyroidism may have 20-30% lower BMR than calculated. This calculator assumes typical metabolism; if you have medical conditions, work with a healthcare provider or registered dietitian for personalized targets. They can factor in medications, health status, and individual variation. Don't rely solely on calculator estimates if you have known metabolic issues. Medical professionals can also order metabolic testing (indirect calorimetry) for more accurate personal BMR measurement if needed.

Be honest and conservative. If you exercise 3 days/week but have a desk job, you're moderately active (1.55), not very active (1.725). If you don't track workouts, default to sedentary (1.2) or lightly active (1.375). Overestimating activity is the most common mistake—it leads to eating more than your actual TDEE, making weight loss harder. You can always increase the multiplier if results show you're more active. Better to start conservative, see real-world results, then adjust upward if needed. If unsure, pick the lower category and monitor actual weight changes; your body will tell you if the estimate is accurate.

This calculator is designed for adults 18-65 with typical body composition. It may not be accurate for: very muscular/athletic individuals (higher actual BMR), extremely obese individuals (lower BMR relative to weight), elderly people (may underestimate), children/teens (different formulas available), medical conditions affecting metabolism (thyroid, PCOS, diabetes), or people on medications affecting metabolism. For these populations, work with healthcare professionals. Also, BMR alone doesn't account for NEAT (Non-Exercise Activity Thermogenesis)—fidgeting, occupational activity, spontaneous movement—which varies greatly between individuals and can add 200-800 cal/day variation.