What the number represents
Your BMR is a floor, not a target. It covers the energy your organs use when you are doing nothing at all. Everything else you do, from walking to training, is on top of it.
It depends mainly on body size and composition. Heavier and taller people burn more, men burn more than women of the same size, and BMR declines gradually with age, which is why the age term is subtracted in each formula.
Three formulas, compared
Mifflin–St Jeor uses weight, height, age and sex. The revised Harris–Benedict equation uses the same inputs with different coefficients. Katch–McArdle uses only lean body mass, so it needs a body fat percentage, which you can add under More options.
Seeing them side by side shows the realistic range. Pick one and use it consistently when tracking progress.
What affects your BMR
Muscle mass raises it, and crash dieting can lower it. Illness, thyroid conditions, pregnancy and some medications all matter and are not captured by any formula. If you suspect your metabolism is unusual, a clinician can measure it directly.
Questions people ask
What is BMR?
Basal metabolic rate is the energy your body needs just to stay alive at rest: breathing, circulation, temperature control and cell repair. It is typically 60–70% of the calories you burn in a day.
Which BMR formula is best?
Mifflin–St Jeor (1990) is generally regarded as the most accurate for most adults and is the headline figure here. Harris–Benedict is older; this page uses the 1984 revision. Katch–McArdle can be more accurate if you know your body fat, because it is based on lean mass.
Why do the formulas give different numbers?
They were built from different groups of people and use different inputs. Differences of 5–10% are normal. If two results are close, you can be more confident in them; if they differ, use the one that suits you best.
What is the difference between BMR and RMR?
BMR is measured under strict, fasted, fully rested conditions. Resting metabolic rate (RMR) is measured less strictly and is slightly higher. The equations on this page are really estimates of RMR, but the two terms are widely used interchangeably.
How do I use my BMR for weight loss?
Do not eat at your BMR. Multiply it by an activity factor to get daily needs, which the TDEE calculator does, then subtract a modest amount for weight loss.