Diet & Energy · Mifflin-St Jeor

BMR Calculator

Your Basal Metabolic Rate — the calories your body burns at complete rest, just to keep you alive.

Age (years)

YRS

Height (cm)

Weight (kg)

What this means

BMR is the energy your body needs lying still all day — before any walking, exercise, or digestion. Multiply it by an activity factor to get your full daily calorie need (use the TDEE Calculator for that).

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Your BMR — live result

Profile: Male · 28 yrs

1680

kcal / day at rest

Sedentary TDEE (×1.2)

2016 kcal

Per kg bodyweight

24.7 kcal/kg

BMR is estimated using the Mifflin-St Jeor equation, considered the most accurate widely-used formula for most adults. It is a general estimate, not a clinical measurement — actual metabolic rate varies by muscle mass, genetics, and health conditions.

What is BMR?

Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest — just to keep you alive. It accounts for the energy required to maintain vital functions such as breathing, circulation, cell production, protein synthesis, and maintaining body temperature. Even if you stayed in bed all day without moving, your body would still burn this many calories.

BMR typically accounts for 60–75% of total daily calorie expenditure, making it the single largest component of your energy needs. Understanding your BMR is the essential first step before calculating your full daily calorie requirements.

How to Use This BMR Calculator

Enter your age, height, weight, and select your gender. Your BMR updates instantly using the Mifflin-St Jeor equation — the most accurate widely-used BMR formula for the general adult population. The result shows how many calories your body needs at complete rest, plus a sedentary TDEE estimate (BMR × 1.2) for a completely inactive day.

The Mifflin-St Jeor Equation

Our calculator uses the Mifflin-St Jeor equation, published in 1990 and validated across multiple large studies as the most accurate formula for predicting resting metabolic rate in most adults:

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

The Harris-Benedict equation (1919) was the original standard but has been shown to overestimate BMR by 5–15% in many individuals. The Mifflin-St Jeor formula corrects for this and is now the preferred equation in clinical nutrition practice.

What Affects Your BMR?

Factors that increase BMR:

Muscle mass: Muscle tissue burns approximately 6 calories per pound per day at rest — significantly more than fat tissue (2 calories/lb). Building muscle is the most effective long-term strategy for raising BMR.
Height and weight: Larger bodies require more energy to maintain. BMR rises with both height and weight.
Age (in youth): Children and teenagers have higher BMRs relative to size due to growth demands.
Stress hormones: Short-term elevations in cortisol and adrenaline temporarily increase metabolic rate.

Factors that decrease BMR:

Age: BMR declines approximately 1–2% per decade after age 20, primarily due to muscle loss.
Crash dieting: Severe calorie restriction triggers adaptive thermogenesis — the body slows metabolism to conserve energy. This is why very low calorie diets often plateau quickly.
Hypothyroidism: An underactive thyroid significantly reduces metabolic rate. If you suspect this, consult a doctor.
Sedentary lifestyle: Inactivity accelerates muscle loss, which reduces BMR over time.

BMR vs TDEE — What is the Difference?

BMR is your calorie need at complete rest. Your Total Daily Energy Expenditure (TDEE) is what you actually burn in a full day, including all activity. TDEE = BMR × an activity multiplier. Use our TDEE Calculator to calculate your full daily calorie needs based on your activity level.

Activity Level	Multiplier	Example
Sedentary	× 1.2	Desk job, no exercise
Light	× 1.375	1–3 workouts/week
Moderate	× 1.55	3–5 workouts/week
Active	× 1.725	6–7 workouts/week
Very Active	× 1.9	Physical job + daily training

How to Use Your BMR for Weight Management

Your BMR sets the floor for safe calorie intake. Eating below your BMR for extended periods is not recommended — it triggers muscle loss and metabolic adaptation. For healthy weight loss, create a deficit from your TDEE, not your BMR.

Calculate TDEE using our TDEE Calculator
Use the Calorie Deficit Calculator to find a safe calorie target
Set protein intake using our Protein Intake Calculator to preserve muscle
Use the Macro Calculator for a complete nutrition plan

Fit4rEver Editorial Standards: All calculator outputs are general estimates for healthy adults. For full limitations, read our Health Disclaimer. For data usage, see our Privacy Policy. Use of this tool indicates agreement with our Terms of Service. Meet our expert team or read our articles for deeper guidance.

Frequently Asked Questions

Should I eat below my BMR to lose weight?

No. Consistently eating below your BMR triggers muscle loss and metabolic adaptation, making long-term weight management harder. Always create your calorie deficit from TDEE, not BMR. A deficit of 300–500 calories from TDEE is the recommended safe range.

Can I increase my BMR?

Yes. The most effective way to raise BMR is building muscle through resistance training. More muscle mass means more calories burned at rest. Adequate protein intake and avoiding crash diets also help preserve and build metabolic rate over time.

Why does BMR decrease with age?

BMR declines with age primarily because of sarcopenia — the progressive loss of muscle mass that begins in the 30s. Since muscle burns more calories at rest than fat, less muscle means a lower BMR. Resistance training is the most powerful tool for slowing this decline.

Is the Mifflin-St Jeor equation accurate for everyone?

It is the most accurate widely-used formula but still an estimate. Individual metabolic rate varies by genetics, hormone levels, and body composition. Use your BMR result as a starting point and adjust based on real-world results over 2–3 weeks.

Related Calculators

Sources

Mifflin MD, et al. A new predictive equation for resting energy expenditure. American Journal of Clinical Nutrition. 1990;51(2):241-247.
Frankenfield D, et al. Comparison of predictive equations for resting metabolic rate. Journal of the American Dietetic Association. 2005;105(5):775-789.
Hall KD, et al. Energy balance and its components. American Journal of Clinical Nutrition. 2012;95(4):989-994.