OmniCalc

BMR Calculator

Health & Fitness

Basal Metabolic Rate calculation

A BMR calculator estimates your Basal Metabolic Rate — the number of calories your body burns just to stay alive at complete rest, powering your heartbeat, breathing, brain function, and cell repair before you take a single step. Our calculator uses the Mifflin-St Jeor equation, published in 1990 and now considered the most accurate widely-used formula, replacing the older Harris-Benedict equation from 1919.

The formulas differ slightly by sex: for men, BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5. For women, BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161. Enter your weight, height, age, and sex, and the calculator returns your BMR in calories per day almost instantly.

BMR is not the same as the total calories you burn in a day — that number, called Total Daily Energy Expenditure (TDEE), multiplies your BMR by an activity factor to account for movement, exercise, and digestion. BMR is the foundation of that calculation and typically accounts for 60–75% of total daily calorie burn in a sedentary adult.

Why BMR Calculator Matters

BMR is the starting point for virtually every evidence-based calorie or diet plan. Whether you're trying to lose fat, gain muscle, or simply maintain your current weight, you need to know your baseline calorie burn before you can set an accurate calorie target — eating below your BMR for extended periods can slow metabolism and cause muscle loss, while wildly overestimating it leads to stalled weight loss or unintended weight gain.

BMR also explains why calorie needs vary so much between individuals of the same weight. Age, height, sex, and body composition all affect resting metabolism — a taller, younger, more muscular person burns significantly more at rest than a shorter, older person at the same body weight, because BMR is driven largely by lean body mass.

Understanding your BMR helps you interpret weight loss plateaus. Metabolism naturally declines by roughly 1–2% per decade after age 20, and BMR also drops as body weight decreases (since a lighter body needs fewer calories to maintain itself) — which is why calorie targets often need periodic recalculation during a long weight loss journey.

The BMR Calculator Formula, Explained

Men: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5. Women: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age − 161

Where: weight = body weight in kilograms, height = standing height in centimeters, age = age in years, BMR = basal metabolic rate in calories (kcal) per day.

The Mifflin-St Jeor equation was derived from measured resting energy expenditure in a large modern sample and is considered more accurate than the older Harris-Benedict equation, which tends to overestimate BMR by 5–10% for many people, particularly those who are overweight.

To estimate your Total Daily Energy Expenditure (TDEE) — the calories you actually burn including activity — multiply BMR by an activity factor: 1.2 (sedentary), 1.375 (lightly active), 1.55 (moderately active), 1.725 (very active), or 1.9 (extremely active).

How to Use the BMR Calculator: Step by Step

  1. Enter your weight

    Input your current body weight in kilograms or pounds — the calculator converts automatically if needed.

  2. Enter your height

    Input your height in centimeters, or feet and inches — this is converted to centimeters for the formula.

  3. Enter your age and sex

    Provide your age in years and select male or female, since the formula uses a different constant for each.

  4. Review your BMR

    The calculator returns your basal metabolic rate in calories per day — the energy you burn at complete rest.

  5. Apply an activity multiplier for TDEE

    Multiply your BMR by an activity factor (1.2–1.9) to estimate your total daily calorie burn including movement and exercise.

BMR Calculator Examples: Real-World Scenarios

1

Woman, Sedentary Office Job

Sarah is a 30-year-old woman who weighs 70 kg and is 165 cm tall. She wants her BMR before calculating a calorie deficit.

Weight:70 kg
Height:165 cm
Age:30
Sex:Female

Calculation

BMR = 10×70 + 6.25×165 − 5×30 − 161 = 700 + 1031.25 − 150 − 161

Result

BMR: 1,420 calories/day. At a sedentary activity level (×1.2), her estimated TDEE is about 1,704 calories/day.

2

Man, Moderately Active

Tom is a 40-year-old man who weighs 85 kg and is 180 cm tall, exercising 3–4 times per week.

Weight:85 kg
Height:180 cm
Age:40
Sex:Male

Calculation

BMR = 10×85 + 6.25×180 − 5×40 + 5 = 850 + 1125 − 200 + 5

Result

BMR: 1,780 calories/day. At a moderately active level (×1.55), his estimated TDEE is about 2,759 calories/day.

3

BMR vs. TDEE Comparison

Ana is a 28-year-old woman who weighs 60 kg and is 160 cm tall. She wants to see the difference between resting burn and total burn on both a sedentary and moderately active schedule.

Weight:60 kg
Height:160 cm
Age:28
Sex:Female

Calculation

BMR = 10×60 + 6.25×160 − 5×28 − 161 = 600 + 1000 − 140 − 161 = 1,299. Sedentary TDEE = 1,299×1.2 = 1,558.8. Moderately active TDEE = 1,299×1.55 = 2,013.5

Result

BMR: 1,299 calories/day. Sedentary TDEE: ~1,559 calories/day. Moderately active TDEE: ~2,014 calories/day — a 455-calorie difference from activity level alone.

Common Mistakes to Avoid

  • Eating below BMR for extended periods to lose weight faster — this can trigger muscle loss and metabolic adaptation, making long-term weight management harder, not easier.
  • Confusing BMR with TDEE and setting a calorie target directly at BMR — BMR excludes all daily activity, so eating at BMR level while active creates a much larger deficit than intended.
  • Not recalculating BMR after significant weight change — BMR drops as weight decreases, so a calorie target set at the start of a diet becomes too high after losing 15–20 lb.
  • Using outdated Harris-Benedict results instead of Mifflin-St Jeor — Harris-Benedict tends to overestimate BMR by 5–10%, which can stall weight loss if used to set calorie targets.

Tips & Tricks

  • Recalculate your BMR every 10–15 lb of weight change to keep calorie targets accurate throughout a diet.
  • Use the TDEE figure, not BMR alone, when setting a daily calorie target for weight loss or maintenance.
  • Strength training helps preserve lean muscle mass during weight loss, which keeps BMR higher than a diet-only approach would.

BMR tells you the calorie floor your body needs just to function at rest — the essential baseline for any calorie planning. Multiply it by an activity factor to get your TDEE, then use the Calorie Calculator to set a realistic deficit or surplus for your goals. Pairing your BMR with the Ideal Weight Calculator or Body Fat Percentage Calculator gives a fuller picture of where your metabolism and body composition currently stand.

BMR Calculator — Frequently Asked Questions

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Calorie Calculator

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Ideal Weight Calculator

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Macro Calculator

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Body Fat Percentage Calculator

see how body composition affects metabolism

Authoritative References

NIH — Body Weight Planner

nih.gov — National Institutes of Health tool and guidance on energy balance and metabolism

Harvard T.H. Chan School of Public Health — Calories

hsph.harvard.edu — Academic explanation of calorie needs and metabolic rate

CDC — Balancing Calories

cdc.gov — Government reference on calorie balance and energy expenditure

External links open in a new tab. OmniCalc.us is not affiliated with these organisations.

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