About you
What your body burns doing nothing
Basal metabolic rate is the energy spent just lying still all day — keeping the heart beating and body temperature steady. It is the largest single share of daily burn; multiply it by an activity factor to get what you actually use in a day.
Why two formulas
Harris-Benedict is the older, more widely known formula and tends to run a little high. Mifflin-St Jeor is newer and generally rated as the better fit for people today. Showing both side by side makes it obvious this is an estimate, not a precise measurement — neither pins down any one person's real rate exactly.
Body composition is not in the formula
Both formulas use only sex, age, height, and weight. Two people with identical numbers can have very different real BMRs if one carries more muscle, since muscle burns more at rest than fat does. Neither formula sees that difference.
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Frequently asked questions
QWhich number should I trust more?
Mifflin-St Jeor is generally considered the better fit for modern populations, but treat both as estimates rather than either one being exactly correct for you.
QCan I eat below my BMR to lose weight faster?
That is not advised. Build your deficit from total daily expenditure (BMR times an activity factor), not from BMR alone — eating below basal rate for long risks muscle loss and other problems.