Free BMR Calculator

Understanding Basal Metabolic Rate (BMR)

Basal metabolic rate (BMR) refers to the energy your body consumes to keep vital processes running while you are completely at rest. These processes include breathing, blood circulation, temperature control, nerve transmission, and cellular maintenance. A large portion of BMR is dedicated to preserving ion gradients across cell membranes and regulating fluid volumes—work that continues even during sleep. The brain, central nervous system, and liver are the organs with the highest resting energy demand. Typically, BMR constitutes 60% to 75% of your total daily energy expenditure (TDEE). Because BMR forms the foundation of daily calorie needs, knowing your personal BMR is essential for designing effective nutrition and fitness plans.

How to Use This Free BMR Calculator

This free basal metabolic rate calculator applies the Mifflin St Jeor equation, widely accepted as the most accurate formula for estimating resting energy expenditure. The calculator accepts both metric and imperial units and automatically converts them, so no manual conversion is needed. To obtain your BMR:

• Enter your current weight in the chosen unit.
• Enter your height in the corresponding unit.
• Provide your age in years (the formula expects a whole number).
• Select your gender (male or female).

After entering these values, the tool instantly displays your BMR in kilocalories per day. This number represents the minimum energy your body requires each day. Additional features, such as reference charts and personalized tips, are available to help you interpret your result.

The Mifflin St Jeor Equation

The Mifflin St Jeor equation was introduced in 1990 and has become the gold standard for BMR estimation, replacing the older Harris-Benedict formula. The equation uses weight, height, age, and a gender-specific constant:

$$\text{BMR (kcal/day)} = 10 \times \text{weight (kg)} + 6.25 \times \text{height (cm)} - 5 \times \text{age (y)} + s$$

where $s = +5$ for men and $s = -161$ for women.

Example Calculation for a Man

Take a 60‑year‑old man weighing 68 kg (150 lb) and 162.5 cm tall (about 5'4"). Plugging the numbers into the formula:

$$\begin{aligned} \text{BMR} &= 10 \times 68 + 6.25 \times 162.5 - 5 \times 60 + 5 \\ &= 680 + 1015.625 - 300 + 5 \\ &\approx 1401 \text{ kcal/day}. \end{aligned}$$

Thus, at complete rest, this man's body burns approximately 1,401 calories per day.

Example Calculation for a Woman

Now consider a 25‑year‑old woman weighing 60 kg (132 lb) and 172.7 cm tall (about 5'8"). Using the female version of the Mifflin St Jeor equation:

$$\begin{aligned} \text{BMR} &= 10 \times 60 + 6.25 \times 172.7 - 5 \times 25 - 161 \\ &= 600 + 1079.375 - 125 - 161 \\ &\approx 1393 \text{ kcal/day}. \end{aligned}$$

These worked examples illustrate how differences in age, weight, height, and gender translate into distinct BMR values.

Other BMR Formulas

Although this calculator uses the Mifflin St Jeor equation, other formulas exist. The Harris‑Benedict equation, published in 1919 and later revised, was the standard for many decades. The Katch‑McArdle formula accounts for lean body mass and is sometimes used to estimate resting daily energy expenditure (RDEE). However, the Mifflin‑St Jeor equation has consistently demonstrated superior accuracy in validation studies.

BMR vs. Resting Metabolic Rate (RMR)

BMR and RMR are related but not identical. RMR includes the energy required to digest and absorb food (the thermic effect of food), which adds roughly 10% to the resting energy number. Therefore, RMR is typically slightly higher than BMR. BMR is measured under more stringent conditions: upon waking, after a 12‑hour fast, and in a thermoneutral environment. The calculator provided here estimates BMR rather than RMR.

Factors That Influence BMR

Multiple factors can raise or lower your BMR:

• Body composition: Lean tissue (muscle) consumes more energy at rest than fat tissue. Individuals with higher fat‑free mass (FFM) generally have a higher BMR.
• Age: BMR rises during growth, then declines in adulthood—on average, 1–2% per decade after age 20—mostly due to loss of muscle.
• Sex: Men tend to have a higher BMR than women because they typically possess more muscle and less fat.
• Genetics: Variations in inherited metabolism can cause BMR to differ among people with similar size and body composition.
• Physical activity: Regular aerobic and resistance exercise can boost muscle mass and elevate BMR.
• Body temperature: Fever increases BMR because chemical reactions speed up with heat.
• Environmental temperature: Cold exposure forces the body to produce additional heat, raising energy expenditure.
• Hormones: Thyroid hormones are the primary metabolic regulators; hyperthyroidism raises BMR, hypothyroidism lowers it.
• Pregnancy: The developing fetus adds its own metabolic demand, increasing the mother's total BMR.

From BMR to Total Daily Energy Expenditure

Your BMR is the baseline. To find your total daily energy expenditure (TDEE), you must add calories used for physical activity (which can account for 15–30% of TDEE depending on activity level) and the thermic effect of food (about 10%). With your BMR and TDEE, you can create a calorie target that supports your goals—weight loss, maintenance, or gain. For example, a modest deficit of 500 kcal/day below TDEE typically leads to about 0.5 kg of weight loss per week.

Disclaimer: This calculator provides estimates for informational purposes only. It is not a substitute for professional medical advice. Consult a healthcare provider for personalized guidance.