NumberTally BMR Calculator — Basal Metabolic Rate (Mifflin-St Jeor)
Calculate your basal metabolic rate — the calories your body burns at complete rest — with the Mifflin-St Jeor equation, and compare it against the Harris-Benedict and Katch-McArdle formulas side by side.
Advanced options
Unlocks the Katch-McArdle formula, which is based on lean body mass instead of total weight.
Shows what your BMR means at sedentary, light, and moderate activity.
What BMR actually is
Your basal metabolic rate is the energy your body spends just existing: heartbeat, breathing, brain activity, body temperature, cell repair. It’s measured at complete rest, and for most people it accounts for roughly 60–75% of all calories burned in a day.
Three things move it most: lean mass (muscle burns more than fat, which is why Katch-McArdle asks for body fat %), size (bigger bodies cost more to run), and age (BMR drifts down about 1–2% per decade after 20 as muscle mass declines). That age slide is one reason strength training matters more, not less, as you get older.
BMR vs TDEE — don’t confuse the two
BMR is your idle burn; TDEE (total daily energy expenditure) is BMR plus everything you actually do. The comparison box below translates your BMR into real-world daily burn at three activity levels — that’s the number to eat around for weight goals, not the BMR itself.
Estimates only — not medical advice. Talk to a healthcare professional about your health.
Frequently Asked Questions
What is a good BMR?
There’s no universal “good” — a healthy BMR simply matches your size, age, and sex. Typical adult values run roughly 1,200–1,800 for women and 1,500–2,200 for men. What matters more is the TDEE built on top of it.
Why is my BMR lower than my friend’s BMR?
Mostly size and composition: a taller, heavier, or more muscular person has more tissue to maintain. Age and sex shift it too — the three formulas above show how each factor plays in.
Can I increase my BMR?
Modestly. Building muscle raises it (muscle is metabolically expensive), and staying active keeps the age-related decline slower. Crash dieting does the opposite — prolonged very-low intake can suppress BMR temporarily.
Does BMR change with age?
Yes — it falls roughly 1–2% per decade after age 20, mostly because muscle mass declines. The Mifflin-St Jeor equation bakes this in with its −5 kcal per year term, which the step-by-step box shows with your numbers.
Is my BMR the number of calories I should eat each day?
No — that’s your TDEE, which is higher. Eating at BMR long-term usually under-fuels you once activity is included. Use the TDEE equivalents below for daily targets.