What BMR means
Your basal metabolic rate is the energy your body uses just to stay alive — breathing, circulation, cell repair. The Mifflin-St Jeor equation for men is 10 × kg + 6.25 × cm − 5 × age + 5 (women subtract 161). An 80 kg, 180 cm, 30-year-old man gets 1780 kcal/day. To plan meals, split this with the macro calculator. The classic alternative equation is available in the Harris-Benedict calculator.
From BMR to daily needs
BMR is calories at rest. Multiply it by an activity factor (roughly 1.2 sedentary to 1.9 very active) to estimate total daily burn. This is a general wellness estimate, not medical advice. Talk to a healthcare professional for personal guidance.
As a rough guide, use 1.2 for a desk job with little exercise, 1.375 for a couple of light sessions a week, 1.55 for moderate training most days, and 1.725 or above for physical work or hard daily training. Multiply by an activity factor and you get the figure from the maintenance calorie calculator.
Why the figures differ
More lean mass means a higher BMR, which is why the lean body mass calculator helps explain differences between people of the same weight. BMR also drops slowly with age.
Sleep, illness, dieting history and hormones all nudge the figure. Long spells of heavy calorie restriction lower resting burn slightly beyond what the weight loss alone explains, while adding muscle through strength training pushes it back up over months. Because the equation is fitted to population averages, treat the result as a starting point: eat around it for two or three weeks, watch the weight trend, and adjust by 100-200 kcal if reality disagrees with the maths. At complete rest the closely related figure is measured by the RMR calculator.
Frequently asked questions
- What is BMR?
- The number of calories your body burns at complete rest to keep you alive.
- Which equation is used?
- The Mifflin-St Jeor equation, widely regarded as accurate for most adults.
- How do I get total calorie needs?
- Multiply BMR by an activity factor from about 1.2 (sedentary) to 1.9 (very active).
- Why is my BMR different from someone the same weight?
- Lean mass, age and sex all change BMR, so two people at the same weight can differ.
- Should I eat only my BMR calories?
- No. BMR covers only what your body burns lying still, so eating at that level leaves nothing for movement, work or digestion. Multiply by an activity factor first, and treat the figure as a general estimate rather than medical advice.