Find out how many calories your body burns at complete rest. Enter your stats below — results include both Mifflin–St Jeor and Katch–McArdle estimates.
Your stats
yrs
lbs
ft
in
cm
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calories / day — your BMR (at rest)
Both formula estimates
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Mifflin–St Jeor
Best for general population
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Katch–McArdle
Requires body fat %
TDEE estimates from your BMR
Activity level
TDEE (kcal/day)
Use the full TDEE calculator to select your activity level and get macro targets.
What is Basal Metabolic Rate (BMR)?
Your Basal Metabolic Rate is the number of calories your body burns each day at complete rest — essentially what you'd burn if you lay in bed all day without moving. It represents the minimum energy needed to keep your vital organs functioning: heart beating, lungs breathing, kidneys filtering, and cells repairing.
BMR accounts for roughly 60–75% of total daily calorie expenditure for most people. The rest comes from physical activity (15–30%) and the thermic effect of food (around 10%). This is why even "sedentary" people burn considerably more than their BMR — daily movement, digestion, and basic tasks all add up.
BMR is the floor of your calorie intake. Eating consistently below your BMR causes muscle loss, hormonal disruption, and metabolic adaptation. Even aggressive cutting diets should stay above BMR.
BMR formulas explained
Mifflin–St Jeor (1990) is the most widely validated equation for the general population and is the default here. Peer-reviewed studies consistently show it has the smallest mean error versus measured BMR for non-athletic individuals.
Katch–McArdle (1975) uses lean body mass instead of total weight, making it significantly more accurate for athletes, bodybuilders, and anyone with above-average muscle mass or below-average body fat. To use it, you need a reasonable estimate of your body fat percentage.
Katch–McArdle: BMR = 370 + (21.6 × lean body mass in kg)
Where lean body mass = weight × (1 − body fat % / 100)
The Harris–Benedict equation (1919, revised 1984) was the gold standard for decades but is now considered slightly less accurate than Mifflin–St Jeor for the modern population. It is not used here, but its values typically run 5–15% higher than Mifflin–St Jeor.
What affects your BMR?
Muscle mass is the single biggest factor — muscle burns approximately 3× more calories at rest than fat tissue. Two people of identical weight can have BMRs differing by 300+ calories if their body composition is significantly different.
Age reduces BMR by approximately 1–2% per decade after 25, primarily due to natural reductions in muscle mass (sarcopenia) unless countered by resistance training.
Sex affects BMR significantly — men typically have 5–15% higher BMR than women of the same age, weight, and height, largely due to higher average muscle mass and lower average body fat percentage.
Thyroid function has a major impact on metabolic rate. Hypothyroidism can reduce BMR by 20–40%, while hyperthyroidism raises it significantly. If your real-world calorie results differ dramatically from this calculator's estimates, thyroid function is worth investigating with a doctor.
Frequently asked questions
What is the difference between BMR and TDEE?
BMR is your calorie burn at complete rest. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity multiplier that accounts for exercise and daily movement. For a moderately active person, TDEE is approximately 1.55× BMR. Use the TDEE calculator to factor in your activity level.
Should I eat at my BMR or TDEE?
Eat at (or relative to) your TDEE — not your BMR. BMR is the absolute minimum your body needs at rest. Since you move, exercise, and digest food throughout the day, eating only at BMR would create a large deficit for most people and risk muscle loss and fatigue. Use TDEE as your baseline and create a deficit from that.
Why are the two formula results different?
Mifflin–St Jeor uses total body weight, while Katch–McArdle uses lean body mass. If you have average body composition, the results will be close. If you are particularly muscular or have high body fat, the difference may be 100–250+ calories. The Katch–McArdle result is more accurate when body fat % is known.
Can BMR change over time?
Yes. BMR decreases with age and during prolonged calorie restriction (metabolic adaptation). It increases with gaining muscle mass. This is why recalculating every 4–8 weeks during a diet is important — as you lose weight, your BMR decreases and calorie targets need adjusting.
Is BMR the same as RMR?
Not exactly. RMR (Resting Metabolic Rate) is measured after a period of rest but not under the strict fasting and temperature conditions required for true BMR. RMR is typically 10–20% higher than BMR. Most calculators, including this one, technically calculate RMR but use the term BMR colloquially, as do most nutrition applications.