BMR Calculator

Mifflin-St Jeor Equation

The Mifflin-St Jeor equation is the primary formula shown in this calculator. Published in 1990 by Mifflin, St Jeor, and colleagues as an improvement over older prediction equations, it estimates Basal Metabolic Rate from four variables: weight in kilograms, height in centimeters, age in years, and sex.

Weight has the largest coefficient (10), so body mass affects BMR more than height or age. The age term subtracts 5 calories per year, reflecting the gradual metabolic slowdown that comes with aging. The Academy of Nutrition and Dietetics recommends Mifflin-St Jeor as the most reliable predictive equation for most healthy adults.

Harris-Benedict (Revised)

The original Harris-Benedict equation dates to 1919 and was one of the first widely used BMR formulas. Roza and Shizgal revised it in 1984, updating the coefficients with more modern data while keeping the same functional form.

This calculator displays Harris-Benedict as a secondary reference so you can compare the two estimates. The formulas use different coefficients and intercepts, so they produce different values for the same inputs. Harris-Benedict tends to run slightly higher than Mifflin-St Jeor for most people, particularly men. Seeing both results gives you a reasonable range rather than a single point estimate.

Schofield Equation (Kids & Teens)

The Mifflin-St Jeor and Harris-Benedict equations were built and validated for adults, so this calculator does not apply them to anyone under 18. For ages 1–17 it uses the Schofield weight-only equation, published by W.N. Schofield in 1985 and adopted by the World Health Organization. Schofield uses separate coefficients for each age band and sex, which is why a growing child's estimate can't come from a single adult formula.

The full Schofield set covers six age bands: under 3, 3–10, 10–18, 18–30, 30–60, and 60 and over. Because children's energy needs vary widely with growth and development, treat a child's or teen's result as a rough estimate and talk to a pediatrician before acting on it.

Choosing a Formula

For adults, you can pick which equation drives your result. Mifflin-St Jeor is selected by default and is the equation the Academy of Nutrition and Dietetics recommends for most healthy adults. Harris-Benedict is offered as a well-known alternative, and Schofield rounds out the set for direct comparison. Whichever you choose becomes the headline number and the basis for the TDEE table; the other equations are shown underneath as secondary estimates so you can see the spread.

The three formulas can differ by 100–200 calories for the same person because they were derived from different study populations. If you're unsure, stick with Mifflin-St Jeor. Seeing all three together is a reminder that any BMR figure is an estimate, not an exact measurement.

How TDEE Is Derived

Total Daily Energy Expenditure (TDEE) is your BMR scaled up by an activity multiplier. The multipliers come from a standard five-level scale used across nutrition science:

• Sedentary (1.2): desk job, little or no exercise
• Lightly active (1.375): light exercise 1–3 days per week
• Moderately active (1.55): moderate exercise 3–5 days per week
• Very active (1.725): hard exercise 6–7 days per week
• Extra active (1.9): very hard exercise plus a physically demanding job

TDEE is computed from the unrounded BMR of whichever formula you selected (Schofield for under-18), then rounded to the nearest whole number. This avoids compounding rounding error. The same activity multipliers apply at every age.

Unit Conversion

All three formulas operate on metric inputs. When you enter imperial measurements, they're converted before the formula runs:

These are the same conversion factors used by the BMI calculator. The conversion happens internally; you always see results in calories regardless of which unit system you use.

Why Men and Women Get Different Results

Men typically carry more lean muscle mass than women at the same height and weight, and muscle tissue burns more calories at rest than fat tissue. The formulas account for this with sex-specific constants.

In Mifflin-St Jeor, the only difference is the final constant: +5 for men, −161 for women. That's a fixed gap of 166 calories per day, all else being equal. Harris-Benedict takes a different approach and uses entirely separate coefficients for each sex, so the gap varies depending on your height, weight, and age.

Typical BMR by Age and Sex

This reference chart uses Mifflin-St Jeor for a man of 178 cm and 82 kg and a woman of 164 cm and 68 kg. Your own BMR depends on your exact height, weight, age, and sex, so run the calculator above for a personal number.