Which BMR formula is most accurate?

Mifflin-St Jeor is considered the most accurate for the general population and is preferred by most registered dietitians. Harris-Benedict (revised 1984 version) is slightly less accurate but widely used. Katch-McArdle is the most accurate for people with known body composition data — it accounts for the fact that lean tissue burns more calories than fat tissue.

Does BMR decrease with age?

Yes, but less than many people think. BMR decreases roughly 1–2% per decade after age 30, primarily because muscle mass tends to decline with age (sarcopenia). The age-related calorie change is real but modest — the bigger driver of weight gain with age is typically decreased activity and calorie tracking drift, not a dramatic metabolic slowdown.

Can I increase my BMR?

Somewhat. The largest modifiable factor is lean body mass — muscle tissue burns 3x more calories at rest than fat tissue. Resistance training and adequate protein intake preserve and build muscle, which modestly raises BMR over time. Crash dieting, conversely, often causes muscle loss and reduces BMR — the mechanism behind 'metabolic adaptation' and weight loss plateaus.

How does BMR relate to calorie counting?

BMR is the floor of your calorie needs. You should never eat below your BMR for extended periods — doing so forces your body to cannibalize muscle for energy. Most people need to eat at their TDEE (BMR × activity factor) to maintain weight, and create a deficit below that for weight loss. Eating at BMR is typically already a significant deficit.

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BMR Calculator

How many calories does your body burn at rest?

What This Does

Your Basal Metabolic Rate is the foundation of every nutrition and weight management calculation. It's the number of calories your body burns in a state of complete rest — just to keep your heart beating, lungs breathing, and organs running. Everything else — exercise, movement, digestion — gets added on top. Understanding your BMR matters because it explains why two people can eat the same amount and have completely different results. Height, weight, age, sex, and lean body mass all influence BMR. A 6'2" man in his 30s burns significantly more at rest than a 5'2" woman in her 50s, even if both are "healthy." This isn't fairness — it's physiology. This calculator uses three different validated formulas. Mifflin-St Jeor is the most accurate for most people. Harris-Benedict is the classic formula (tends to run slightly higher). Katch-McArdle is the most precise if you know your body fat percentage — it's based on lean body mass rather than total weight, so it's more accurate for muscular or very lean individuals. The activity table shows your Total Daily Energy Expenditure at each activity level — that's the calorie intake where your weight stays stable.

When Should You Use This?

→Starting a diet — understand your baseline before creating any deficit
→Explaining why your maintenance calories differ from a partner or friend
→Tracking how BMR changes as you lose weight or gain muscle
→Comparing formula accuracy if you have body composition data (body fat %)
→Educating yourself on why age affects metabolism and weight management

Example Scenario

Carlos is 45, male, 210 lbs, 5'11". His Mifflin-St Jeor BMR is 1,940 calories. He gets his body fat measured at 22% (lean mass: 164 lbs). Katch-McArdle gives 1,901 — close to Mifflin but slightly lower due to higher-than-average body fat for his size. His TDEE at "moderately active" is about 2,972. He's been eating 2,100 calories and wondering why he's losing so slowly — he's in only a 230-calorie deficit, not the 500 he thought. Knowing his actual BMR explains the plateau.

🔥BMR & TDEE Calculator