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BMR Calculator

Calculate your Basal Metabolic Rate using Mifflin-St Jeor or Katch-McArdle.

How this calculator works

Choose a formula: Mifflin-St Jeor (the default, using sex/age/weight/height) or Katch-McArdle (using weight and body fat %, better if you know your lean mass). Then enter your numbers and get your estimated BMR.

The formula

Mifflin-St Jeor (men)   = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Mifflin-St Jeor (women) = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161

Katch-McArdle = 370 + 21.6 × lean body mass(kg)
where lean body mass = weight(kg) × (1 − bodyFat%/100)

Worked example

A 30-year-old man, 80kg (176 lb), 180cm (5’11”):

  • Mifflin-St Jeor: 10×80 + 6.25×180 − 5×30 + 5 = 1,780 kcal/day

If instead he knows his body fat is 20% (lean mass = 80 × 0.8 = 64kg):

  • Katch-McArdle: 370 + 21.6×64 = 1,752.4 kcal/day

Frequently asked questions (FAQ)

What is BMR, and how is it different from the calories I actually burn in a day?

BMR is the energy your body needs at complete rest: just to breathe, circulate blood, and keep cells alive. It doesn't include any movement or activity. For your total daily burn including activity, see our TDEE calculator, which multiplies BMR by an activity level.

Which formula is more accurate, Mifflin-St Jeor or Katch-McArdle?

Mifflin-St Jeor is generally considered the most accurate formula for the general population and doesn't require knowing your body fat percentage. Katch-McArdle can be more accurate for people with unusually high or low muscle mass, since it's based on lean body mass rather than total weight, but it requires an accurate body fat % measurement to be reliable.

Do I need to know my body fat % to use this calculator?

Only if you choose the Katch-McArdle formula. The default Mifflin-St Jeor formula only needs your sex, age, weight, and height. Use our Body Fat calculator first if you want to try Katch-McArdle.

Does BMR change as I lose or gain weight?

Yes. BMR is a function of your current weight, height, and age (or lean mass, for Katch-McArdle), so it changes as your body changes. Recalculate periodically rather than relying on a single number long-term.

Why does age lower BMR in the formula?

Metabolically active tissue (like muscle) tends to decline with age, and metabolic rate tends to slow down as a result. The Mifflin-St Jeor formula reflects this population-level trend with a small downward adjustment per year of age.

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