BMR Calculator
Enter your age, gender, height, and weight to estimate your basal metabolic rate (BMR) using the Mifflin-St Jeor formula.
Last updated: September 5, 2026
Frequently asked questions
What is BMR?
Basal metabolic rate is the number of calories your body burns at complete rest just to maintain vital functions like breathing and circulation - it doesn't include any activity.
How accurate is the Mifflin-St Jeor formula?
It's considered one of the more accurate BMR formulas for the general population, typically within about 10% of measured values, though individual metabolism varies with muscle mass and other factors.
Does BMR change as I age?
Yes - BMR gradually declines with age, largely due to a natural decrease in muscle mass over time, which is part of why calorie needs often trend down in later adulthood even at the same activity level.
Should I eat at exactly my BMR calorie level?
No - BMR is the minimum energy your body needs at complete rest, not a healthy target to eat at. Eating below BMR for extended periods can slow metabolism and cause muscle loss; use your BMR as a baseline and add your activity level to find an appropriate maintenance or deficit target.
How is BMR different from calories burned per day?
BMR only counts the energy your body needs at total rest to keep organs running - it doesn't include walking, exercise, or even digestion. Your actual daily burn (TDEE) is BMR multiplied by an activity factor, which is usually 1.4 to 1.9 times higher than BMR alone.
What's an example BMR calculation?
For a 25-year-old woman, 5'6" (66 in), 140 lb, the Mifflin-St Jeor formula gives roughly 1,410 calories per day. That number represents calories burned lying still for 24 hours, before adding any movement.
Is BMR the same as 'resting metabolic rate' (RMR)?
They're closely related but not identical - BMR is measured under strict lab conditions (fasted, fully rested, controlled temperature), while RMR is a slightly less strict measurement that's typically 10-20% higher. Most online calculators, including this one, estimate BMR-like values using formulas rather than direct measurement, so the term is often used loosely.