Macros
BMI, BMR and TDEE are estimates from general formulas, not medical advice.
This BMR calculator estimates your basal metabolic rate, the calories your body burns at complete rest to keep you alive, using the Mifflin–St Jeor, Harris–Benedict or Katch–McArdle equation. Enter sex, age, height and weight; add body fat for Katch–McArdle. BMR is the starting point for any daily calorie target.
How to use
- Choose metric (cm, kg) or imperial (ft, in, lb) units; your choice is remembered.
- Enter your height and weight. Your BMI, WHO category and healthy weight range appear below.
- On BMR, add your sex and age and pick a formula. Katch–McArdle also needs your body fat percentage.
- On TDEE, pick your activity level to see daily calories to maintain, lose or gain weight and a macro split in grams. Tap any result to copy it.
- These are estimates for healthy adults, not medical advice. Talk to a doctor or dietitian before major changes.
- BMI doesn’t tell fat from muscle: athletes may read as overweight, and older adults may have a normal BMI with little muscle. For children and teens under 20, use BMI-for-age percentiles instead.
- In studies, Mifflin–St Jeor (1990) usually comes closest for most adults. Harris–Benedict uses the 1984 revision. Katch–McArdle uses lean body mass and works best if you know your body fat.
- Calorie targets use about 7,700 kcal per kg (3,500 per lb) of body weight. Very low targets are flagged: most adults shouldn’t go below 1,200 (women) or 1,500 (men) kcal a day without supervision.
- Macros use 4 kcal per gram of protein and carbs and 9 kcal per gram of fat. Nothing you enter leaves your device or is stored.
The three formulas
Mifflin–St Jeor (1990): 10 × kg + 6.25 × cm − 5 × age + 5 for men, −161 for women. For a 30-year-old woman of 165 cm and 60 kg that is about 1,320 kcal a day; for a 30-year-old man of 180 cm and 80 kg about 1,780 kcal. Studies usually find it the closest for most adults.
Harris–Benedict uses the 1984 revised coefficients and tends to read a little higher. Katch–McArdle (370 + 21.6 × lean mass in kg) ignores sex and age and works best when you know your body fat percentage.
BMR versus TDEE
BMR covers only breathing, circulation and other basic functions, which is roughly 60–70% of what most people burn in a day. Digestion and all movement come on top, so your maintenance calories (TDEE) are BMR times an activity factor of 1.2 to 1.9. Eating below your BMR for long periods is not advised without medical supervision.
These are estimates from population formulas, not medical advice, and they are not meant for children, pregnancy or medical conditions. Nothing you enter leaves your device.
Frequently asked questions
What is BMR?
Basal metabolic rate is the energy your body uses at rest in a day for breathing, circulation, temperature and cell repair, before any activity.
Which BMR formula is most accurate?
For most adults Mifflin–St Jeor comes closest in studies. If you know your body fat percentage reliably, Katch–McArdle can be better, especially for lean or muscular people.
Why does BMR fall with age?
The formulas subtract a few calories per year of age because muscle mass and organ metabolism tend to decline. Strength training helps keep muscle.
Should I eat my BMR to lose weight?
No. BMR excludes all activity, so eating at BMR is already a large deficit for most people. Base targets on TDEE instead.
How accurate is a BMR calculator?
Equations are typically within about 10% for most people, but individuals can differ more. Only lab methods like indirect calorimetry measure it directly.