What's the difference between BMR and TDEE?

BMR (basal metabolic rate) is what your body would burn lying still for a whole day. TDEE (total daily energy expenditure) is that plus digesting food and all your moving. TDEE is 1.2 to 1.9 times BMR, set mostly by your daily steps. You plan meals against TDEE. BMR is the floor you shouldn’t eat under.

The two come from the same inputs, your age, sex, height and weight, and they print a few hundred to over a thousand calories apart, depending on your steps. So it’s easy to take the wrong one home. Eating at your BMR is a cut of about 17% of your day if you take under 5,000 steps, and nearly half if you take 12,500 or more.

The simple version

BMR is the car idling in the driveway. TDEE is the whole day of driving. You fill the tank for the driving, and the idle is the least it will ever use.

One body, both numbers

A 40-year-old woman, 5 foot 5 and 160 pounds:

The BMR line uses the Mifflin-St Jeor formula, built in 1990 from lab measurements of 498 adults: 10 times weight in kg, plus 6.25 times height in cm, minus 5 times age, then minus 161 for women or plus 5 for men. The TDEE lines multiply it by the step multipliers our calculators use, 1.2 under 5,000 steps and 1.55 at 7,500 to 9,999, then give or take 10%, since the formula lands within 10% for about four people in five. Under 5,000 steps, 500 under the middle would be 1,180, below her BMR, so her target stops at about 1,400. Calculators often call the first number RMR (resting metabolic rate). The Mifflin formula was fitted to resting measurements, so on a calculator the two names point to the same number.

What to do

• Get both numbers from the BMR calculator.
• Plan against the middle of your TDEE range, and keep your daily target above your BMR.
• Never go under 1,200 calories a day for women or 1,500 for men without a doctor. Those are the low end of the diets in the 2013 US obesity guideline.