BMR Calculator

Basal Metabolic Rate — calories your body burns at complete rest (Mifflin-St Jeor equation)

Basal Metabolic Rate (BMR) — the calories your body burns at complete rest just to maintain basic life functions — is the foundation that daily calorie needs get built on top of, and the specific formula used to estimate it matters, since different formulas can produce meaningfully different results for the same person.

Why the Mifflin-St Jeor equation specifically

Several BMR estimation formulas exist, but the Mifflin-St Jeor equation (using weight, height, age, and sex) is generally considered more accurate for most modern populations than the older Harris-Benedict equation, which was originally derived from research over a century ago on a population that doesn't necessarily reflect current body composition norms. Mifflin-St Jeor has been validated against measured metabolic rate more recently and consistently shows smaller average error across diverse populations in comparative studies — which is why this calculator uses it as the primary formula rather than the older, still-commonly-cited Harris-Benedict alternative that some other calculators and older references still default to.

A worked example

Two people with identical weight and height but different ages will show different BMR values, since metabolic rate genuinely declines with age (a proportionally larger share of body composition typically shifts toward less metabolically-active tissue over time) — the formula captures this age effect directly, rather than treating BMR as purely a function of body size alone.

How this connects to your other health calculations

BMR is not the same as total daily calorie needs — it's specifically the resting-only figure. The Calorie/TDEE Calculator takes this BMR figure and multiplies it by an activity-level factor to estimate Total Daily Energy Expenditure, which is the actually useful number for setting a calorie target for weight maintenance, loss, or gain. BMR alone, without an activity multiplier, understates real daily calorie needs for anyone who isn't literally at complete bed rest all day.

Common mistakes

Using BMR directly as a daily calorie target — without applying an activity-level multiplier to account for movement, exercise, and daily activity beyond complete rest — significantly understates real calorie needs for almost everyone; BMR is an input to the TDEE calculation, not a standalone daily calorie target.