BMR Calculator

The calculator converts imperial entries first. Height in inches becomes centimeters by multiplying by 2.54. Weight in pounds becomes kilograms by multiplying by 0.453592. Age is in years.

Mifflin-St Jeor starts with this shared base:

$\text{base} = 10 \times \text{weight} + 6.25 \times \text{height} - 5 \times \text{age}$

For males:

$\text{Mifflin-St Jeor BMR} = \text{base} + 5$

For females:

$\text{Mifflin-St Jeor BMR} = \text{base} - 161$

The Harris-Benedict equations displayed as secondary results are:

$\text{male Harris-Benedict} = 66.47 + 13.75 \times \text{weight} + 5.003 \times \text{height} - 6.755 \times \text{age}$

$\text{female Harris-Benedict} = 655.1 + 9.563 \times \text{weight} + 1.85 \times \text{height} - 4.676 \times \text{age}$

TDEE is calculated only from Mifflin-St Jeor:

$\text{TDEE} = \text{Mifflin-St Jeor BMR} \times \text{activity factor}$

The activity factors are 1.2 sedentary, 1.375 light, 1.55 moderate, 1.725 very active, and 1.9 extra active. The displayed BMR and TDEE values are rounded to whole calories per day.

Example: estimating basal metabolic rate

Use the default metric example: male, age 30, height 180 cm, weight 75 kg, sedentary activity. The Mifflin base is 10 times 75 plus 6.25 times 180 minus 5 times 30. That is 750 plus 1,125 minus 150, or 1,725. Adding 5 for male gives 1,730 calories/day, displayed as the primary result.

Harris-Benedict for the same person is:

$66.47 + 13.75 \times 75 + 5.003 \times 180 - 6.755 \times 30$

That equals about 1,795.7, displayed as 1,796 calories/day. Sedentary TDEE uses 1.2 times the Mifflin result, so 1,730 times 1.2 equals 2,076 calories/day. If the activity selection changes, the BMR stays the same while TDEE changes. That separation is important: BMR describes the resting estimate, while activity factor is the calculator’s only adjustment for daily movement, work demands, and exercise habits.

Interpreting the estimate

Mifflin-St Jeor is widely used because it performed well in validation work for resting energy expenditure in many adults. Harris-Benedict is older and can differ noticeably for some body sizes. Neither equation directly measures lean body mass, and neither knows whether your activity factor is accurate. A desk worker who trains hard for an hour but sits the rest of the day may not match the same category as someone with an active job.

For weight management, compare predicted TDEE with actual trends. If body weight is stable for several weeks at a logged intake, that intake is a practical maintenance estimate even if the formula says something else. For body-size context, the BMI calculator and body-fat calculator address different measurements; they should not be confused with resting energy expenditure.

Limitations, disclaimer, and common mistakes

This page is educational only and is not medical advice. It cannot diagnose thyroid disease, metabolic adaptation, malnutrition, or energy deficiency. Ask a clinician or registered dietitian for individualized assessment, especially with unexplained weight change, chronic illness, pregnancy, adolescence, or eating disorder history.

Common mistakes include choosing an activity factor based on aspiration rather than typical weeks, using goal weight instead of current weight without realizing it changes the estimate, and treating BMR as a recommended calorie intake. BMR is below most people’s total needs. Another mistake is comparing calorie targets from different calculators without checking formulas; this page uses Mifflin-St Jeor for the primary value and TDEE, while some tools use Harris-Benedict, Katch-McArdle, or dynamic models.

Sources

• Mifflin MD et al., A new predictive equation for resting energy expenditure in healthy individuals — validation study behind the Mifflin-St Jeor equation.
• NIH NIDDK, Body Weight Planner — clinical research-based explanation of energy balance and weight planning.
• CDC, Physical Activity Guidelines for Adults — public health context for adult activity and movement.