BMR and TDEE calculator

The two numbers

BMR is what your body spends staying alive at complete rest: circulation, breathing, temperature, cell repair. For most adults it is between 60 and 70 percent of everything they burn in a day.

TDEE is BMR multiplied by an activity factor, from 1.2 for desk-bound to 1.9 for a physical job or twice-daily training. That is the maintenance figure. Eat consistently below it and weight falls, above it and weight rises.

Which equation

Mifflin-St Jeor, published in 1990, is the default here because it predicts measured resting energy expenditure more accurately than the older Harris-Benedict equation in most adult populations. The calculator shows the Harris-Benedict figure alongside it so you can see the gap, which is usually small and occasionally not.

Both are population estimates. Individual metabolic rate varies by something like ten percent either side of a prediction for reasons including thyroid function, body composition and genetics. Treat the output as a starting point and adjust from what the scale actually does over three or four weeks.

The activity multiplier is where people go wrong

Almost everyone overestimates it. Three gym sessions a week alongside a desk job is lightly active, not very active. Very active means hard training six or seven days a week. If your weight is not moving on a deficit that should work, the multiplier is the first thing to check, before the calorie target.

Why it appears on a regenerative medicine site

Because weight loss is the intervention with the strongest evidence base for knee osteoarthritis pain, and it is free. Walking loads the knee at three to four times body weight, so a sustained deficit does more for a painful knee than most of what gets sold for it. Clinics that ask patients to lose weight before treating a weight-bearing joint are not stalling, they are improving the odds of the thing you are paying for.