BMR Calculator
Calculate your basal metabolic rate with Mifflin-St Jeor, Harris-Benedict or Katch-McArdle, compare all three, and see the math behind the number.
BMR Calculator: with the default inputs, basal metabolic rate is 1,690.
The equations were fitted separately by sex; pick the one that matches your physiology.
Calories per day your body burns at complete rest.
- Per hour
- 70BMR ÷ 24.
- Mifflin-St Jeor
- 1,690
- Harris-Benedict (revised)
- 1,746
- Katch-McArdle
- —Shown only when you enter a body fat %.
Assumptions
- Mifflin-St Jeor is the default; it predicts resting energy expenditure, used here interchangeably with BMR.
- Harris-Benedict uses the 1984 Roza & Shizgal coefficients, not the 1918 originals.
- Katch-McArdle is only computed when a body fat percentage above 0 is entered.
- Equations are for adults; they are not validated for children, pregnancy or clinical illness.
| Activity level | Multiplier | Daily calories (TDEE) |
|---|---|---|
| Sedentary | 1.2 | 2,028 |
| Lightly active | 1.375 | 2,323 |
| Moderately active | 1.55 | 2,619 |
| Very active | 1.725 | 2,915 |
| Extra active | 1.9 | 3,210 |
Multiply BMR by an activity factor to estimate total daily energy expenditure. The TDEE calculator goes deeper.
How this is worked out
The formula
Mifflin-St Jeor (1990) Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5 Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161 Harris-Benedict, revised by Roza & Shizgal (1984) Men: BMR = 88.362 + 13.397 × weight + 4.799 × height − 5.677 × age Women: BMR = 447.593 + 9.247 × weight + 3.098 × height − 4.330 × age Katch-McArdle BMR = 370 + 21.6 × lean body mass (kg), where LBM = weight × (1 − body fat %)
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Age
- A number.from 15 to 100 · whole numbers only · defaults to 35
- Sex
- The equations were fitted separately by sex; pick the one that matches your physiology.Male · Female
- Height
- A number.in ft, in, cm, m · from 2 to 9 · defaults to 5.8333
- Weight
- A number.in lb, kg, st · from 20 to 1500 · defaults to 165
- Formula(under More options)
- Choose one of 3 options.Mifflin-St Jeor (recommended) · Harris-Benedict (revised 1984) · Katch-McArdle (needs body fat %)
- Body fat(under More options)
- Leave at 0 if unknown. Only Katch-McArdle uses it; estimate it with the body fat calculator.a percentage · from 0 to 70 · defaults to 0
What you get back
- Basal metabolic ratemain answer
- Calories per day your body burns at complete rest.
- Per hour
- BMR ÷ 24.
- Mifflin-St Jeor
- Harris-Benedict (revised)
- Katch-McArdle
- Shown only when you enter a body fat %.
What this assumes
- Mifflin-St Jeor is the default; it predicts resting energy expenditure, used here interchangeably with BMR.
- Harris-Benedict uses the 1984 Roza & Shizgal coefficients, not the 1918 originals.
- Katch-McArdle is only computed when a body fat percentage above 0 is entered.
- Equations are for adults; they are not validated for children, pregnancy or clinical illness.
About this calculator
Basal metabolic rate is the energy your body spends just staying alive — pumping blood, breathing, keeping warm, running the brain and repairing tissue — measured at rest, fasted, in a neutral-temperature room. For most people it's 60–75% of everything they burn in a day, which is why it's the foundation of every calorie target.
Which formula should you use?
- Mifflin-St Jeor (1990) is the default. When the Academy of Nutrition and Dietetics reviewed the prediction equations in 2005 (Frankenfield et al.), it came out most accurate for both normal-weight and obese adults, landing within 10% of measured RMR about 70–80% of the time.
- Harris-Benedict dates from 1918; the 1984 Roza & Shizgal revision fixed some of its bias, but it still runs about 5% high for many modern adults. It's here because it's what many older resources and apps use.
- Katch-McArdle ignores age and sex and works purely from lean body mass, so it's the pick if you know your body fat percentage from a DEXA scan or a reliable skinfold test — especially if you're much leaner or heavier than average. Enter your body fat under More options and it appears alongside the other two.
How to read the result
BMR is not the number of calories you should eat. It's the floor. Eating below it for long stretches isn't a shortcut — it's a signal to your body to slow down. To turn BMR into a daily target, multiply by an activity factor (the table below does this) or use the TDEE and calorie calculators, which share this engine.
Why your real number may differ
Prediction equations explain about 70% of the variation between people. Genetics, thyroid status, muscle mass, recent dieting (which lowers metabolic rate beyond what weight loss alone predicts) and even room temperature move the true figure by ±10–15%. If the estimate looks off, trust your weight trend over a few weeks: if you're holding steady on a known intake, that intake is your real maintenance.
Strictly speaking, what most people measure and call "BMR" is resting metabolic rate (RMR), taken under slightly less strict conditions. The two differ by only a few percent and the equations here are used interchangeably for both.
Frequently asked questions
▸What's the difference between BMR and RMR?
BMR is measured under strict lab conditions (fasted 12 hours, fully rested, thermoneutral). RMR is measured under looser everyday conditions and runs a few percent higher. Prediction equations like Mifflin-St Jeor are used for both.
▸Is it safe to eat below my BMR?
Not as a routine. Your body has to cover its basal needs somehow, and sustained intake below BMR usually leads to muscle loss, fatigue and a lower metabolic rate. Deficits should come off your total daily expenditure (TDEE), not your BMR.
▸Which BMR formula is most accurate?
For most adults, Mifflin-St Jeor. If you have a reliable body fat measurement, Katch-McArdle can be better because it accounts for how much of your weight is muscle.
▸Why does my BMR drop as I age?
Mostly loss of muscle mass and shifts in hormones. Mifflin-St Jeor subtracts 5 kcal per year of age; keeping muscle through resistance training blunts much of the decline.
▸Do these formulas work for very muscular or very overweight people?
Less well. Mifflin-St Jeor still does reasonably for obesity, but for very muscular people it underestimates and for very high body fat it overestimates. Katch-McArdle with a measured body fat percentage corrects for both.
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The questions people ask next to a bmr.
Estimate your total daily energy expenditure from BMR and activity level, see the number at every activity multiplier, and learn what each multiplier really means.
Find how many calories a day to eat to maintain, lose or gain weight, with BMR and TDEE shown, Mifflin-St Jeor by default, and warnings if the target is too low.
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