BMR Calculator

How the BMR Calculator Works

The BMR calculator (Basal Metabolic Rate) computes how many calories your body burns at complete rest — just to sustain organ function, breathing, circulation, neurological activity, and temperature regulation. It uses the Mifflin-St Jeor equation (1990), the most validated BMR formula for the general population. Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5. Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161.

Example: 35-year-old woman, 140 lbs (63.5 kg), 5'5" (165.1 cm). BMR = 10(63.5) + 6.25(165.1) − 5(35) − 161 = 635 + 1,031.9 − 175 − 161 = 1,330.9 cal/day. This is the minimum she needs just to survive at complete rest — any activity above zero adds to this number.

BMR TDEE: From Resting Rate to Daily Calorie Needs

BMR alone doesn't tell you how much to eat — that's TDEE (Total Daily Energy Expenditure). TDEE = BMR × activity multiplier:

• Sedentary (×1.2): Desk job, no exercise. For our example woman: TDEE = 1,331 × 1.2 = 1,597 cal/day
• Lightly active (×1.375): Light exercise 1–3x/week. TDEE = 1,331 × 1.375 = 1,830 cal/day
• Moderately active (×1.55): Exercise 3–5x/week. TDEE = 1,331 × 1.55 = 2,063 cal/day
• Very active (×1.725): Hard training 6–7x/week. TDEE = 1,331 × 1.725 = 2,296 cal/day
• Extra active (×1.9): Athlete + physical job. TDEE = 1,331 × 1.9 = 2,529 cal/day

The TDEE is the number you actually need to eat at to maintain weight. Eat below it to lose weight; above it to gain. Knowing your precise BMR and TDEE is the foundation of any effective nutrition strategy.

BMR by Age, Sex, and Weight — Reference Values

Key BMR reference points to compare against your calculated value:

• 25-year-old man, 180 lbs, 5'10": BMR ~ 1,958 cal/day
• 25-year-old woman, 130 lbs, 5'5": BMR ~ 1,378 cal/day
• 40-year-old man, 190 lbs, 5'11": BMR ~ 1,954 cal/day
• 40-year-old woman, 150 lbs, 5'4": BMR ~ 1,383 cal/day
• 55-year-old man, 185 lbs, 5'10": BMR ~ 1,818 cal/day
• 55-year-old woman, 155 lbs, 5'4": BMR ~ 1,308 cal/day
• 70-year-old man, 175 lbs, 5'9": BMR ~ 1,687 cal/day
• 70-year-old woman, 140 lbs, 5'2": BMR ~ 1,200 cal/day

Men have higher BMR than women at the same weight primarily due to higher muscle mass and testosterone effects on metabolism. BMR decreases approximately 2–3% per decade after age 20, mostly from age-related muscle loss (sarcopenia).

BMR Calculator for Weight Loss

Using BMR for weight loss requires these principles:

• Never eat below BMR for extended periods: Doing so accelerates muscle loss, suppresses metabolism (adaptive thermogenesis), and impairs organ function. Minimum intake = BMR + 10–20% in almost all cases.
• Create deficit from TDEE, not BMR: Target 500 cal below TDEE for approximately 1 lb/week loss. For the woman above (TDEE ~ 2,063 cal at moderate activity), a 500-cal deficit = 1,563 cal/day target — well above her BMR of 1,331.
• Recalculate as you lose weight: Every 10–15 lbs of weight loss reduces BMR by approximately 50–75 cal/day. Adjust your intake target downward as you lose to maintain the intended deficit.
• Prioritize protein: 0.7–1.0g per pound of bodyweight per day preserves muscle mass during a calorie deficit, preventing the BMR decline associated with muscle loss.

BMR Formula Comparison: Which Is Most Accurate?

Three main equations estimate BMR:

• Mifflin-St Jeor (1990): Best overall accuracy for the general population. Validated against indirect calorimetry in multiple studies. Accurate within ±10% for 82% of people. Uses weight, height, age, sex. Our calculator uses this formula.
• Harris-Benedict (revised 1984): Widely used, slightly less accurate than Mifflin for most people. Tends to overestimate BMR for people with obesity by 5–10%.
• Katch-McArdle: Most accurate for people who know their lean body mass: BMR = 370 + 21.6 × LBM(kg). Removes sex as a variable because it directly accounts for muscle mass. Requires DEXA scan or accurate body composition measurement. Best for athletes.

Calories Burned at Rest: What Makes Up BMR?

Your BMR is distributed across organ systems at rest:

• Liver: ~27% of BMR (metabolic hub — processes nutrients, detoxifies, synthesizes proteins)
• Brain: ~19% of BMR (constant energy demand regardless of mental activity level)
• Skeletal muscle (at rest): ~18% of BMR (increases dramatically during exercise)
• Kidneys: ~10% of BMR
• Heart: ~7% of BMR
• Other organs and processes: ~19%

This explains why muscle mass is the most modifiable factor in your BMR: adding muscle increases resting metabolism not just from muscle itself but from the increased demand placed on the liver, heart, and other organs to support that muscle. Each pound of muscle burns approximately 6 cal/day at rest — 5 lbs of additional muscle raises BMR by ~30 cal/day.

Frequently Asked Questions

What is a normal BMR for my age?

For adult women, typical BMR ranges from 1,100–1,600 cal/day. For adult men: 1,500–2,200 cal/day. Values below 1,200 for women or 1,400 for men at healthy weight may indicate a slow metabolism worth investigating — possibly hypothyroidism, history of severe caloric restriction, or significant muscle loss. Your calculated BMR using this tool should be within 10–15% of your actual measured BMR.

Can I increase my BMR?

Yes, through building muscle mass. Resistance training 3–4x/week combined with adequate protein (0.7–1.0g/lb bodyweight) is the most effective method. Adding 10 lbs of muscle over 12–18 months raises BMR by approximately 60 cal/day — modest alone, but combined with improved TDEE from activity, the total impact on body composition over years is significant. Eating adequate calories (not chronically dieting) also keeps metabolism from adapting downward.

How accurate is BMR calculation?

The Mifflin-St Jeor equation is accurate within ±10% for about 82% of people. The other 18% may have metabolisms 10–20% faster or slower than predicted, due to genetics, thyroid function, body composition differences, and other factors. If you consistently can't lose weight at calculated deficits, or consistently gain weight at supposed maintenance, consider getting an actual metabolic rate test (indirect calorimetry) from a hospital or sports medicine clinic. Cost: approximately $150–$350.

What is the difference between BMR and RMR?

BMR (Basal Metabolic Rate) is measured under strictly controlled conditions: after 8+ hours of sleep, 12+ hours of fasting, thermoneutral environment, complete rest. RMR (Resting Metabolic Rate) is measured under resting but not strictly basal conditions — you may have been awake and ambulatory. RMR is slightly higher than BMR by 10–20% in most people. The two terms are often used interchangeably in practice, though technically distinct. Most nutrition calculators use formulas that estimate RMR rather than true BMR.