Why the formulas treat women differently
BMR formulas were built by measuring how many calories real men and women burn at rest. Women tend to carry a higher share of body fat. The American Council on Exercise lists 25% to 31% body fat as average for women and 18% to 24% for men. Lean mass, which includes muscle and organs, drives most of the calories you burn at rest.
That helps explain why the female formulas give a lower number at the same size. With Mifflin-St Jeor, a woman gets 166 fewer calories a day than a man of the same height, weight, and age.
What this version shows you
This page starts with the female setting. For a 40-year-old woman who is 5 ft 5 in (165 cm) and 145 lb (66 kg), you will see:
- Mifflin-St Jeor: about 1,329 calories a day. A 2005 review found this was the most likely of the common formulas to land within 10% of measured values.
- Harris-Benedict (revised): about 1,394 calories a day.
- Katch-McArdle: shows up once you add your body fat %.
Here the first two results are about 65 calories apart. Formulas rarely match exactly, which is a good reminder that every BMR is an estimate. We highlight Mifflin-St Jeor because of that review.
Getting more from your BMR
- Add your body fat. Don't know it? Our body fat calculator for women estimates it with a tape measure.
- Don't eat at your BMR. It leaves out all your movement. Your TDEE is the number to plan meals around.
To read more, see what BMR is, or use the main BMR calculator.