Mifflin-St Jeor Formula
BMR = 10×W + 6.25×H − 5×A + S
W = weight kg · H = height cm · A = age · S = +5 male, −161 female
TDEE = BMR × activity factor (1.2 to 1.9)
TDEE = BMR × Activity Factor (1.2 to 1.9). This is the most validated formula for estimating resting metabolic rate in adults (Mifflin et al., 1990), and the Academy of Nutrition and Dietetics recommends it for healthy adults. See the BMR calculator for the other equations.
Worked example. A 35-year-old man, 175 cm, 70 kg. BMR = 700 + 1,093.75 − 175 + 5 = 1,624 kcal. Moderately active: 1,623.75 × 1.55 = 2,517 kcal a day to maintain. A deficit of 550 kcal gives about 1,967 kcal a day, which at 7,700 kcal per kg works out to about 0.5 kg a week at the start.
How fast to lose weight
The NHLBI practical guide for clinicians recommends cutting 500 to 1,000 calories a day from current intake, which gives a loss of about 1 to 2 pounds (0.5 to 0.9 kg) a week. Its supervised diet plans use 1,000 to 1,200 calories a day for most women and 1,200 to 1,600 for men. Plans that low are meant to be followed with a health professional, so the calculator warns you when a target falls under about 1,200 (women) or 1,500 (men).
The simple "3,500 calories per pound" rule overstates long-term loss. As you lose weight you burn less, so the same deficit produces slower loss over months. The NIDDK Body Weight Planner, built on research at the National Institutes of Health, models this slowdown if you want a longer forecast.
Macros: protein, carbs and fat
The National Academies set Acceptable Macronutrient Distribution Ranges for adults: 45 to 65% of calories from carbohydrate, 20 to 35% from fat and 10 to 35% from protein. The protein RDA is 0.8 g per kg of body weight a day, a minimum for healthy adults. Many people aiming to keep muscle while losing weight eat more than that. One gram of protein or carbohydrate has 4 kcal and one gram of fat has 9 kcal, which is how the grams above are worked out.
Limits of any calorie calculator
Every number here is an estimate from population equations. Real needs can differ by a few hundred calories a day. Track your weight for two to four weeks and adjust. These targets are not meant for pregnancy, breastfeeding, children, teens, or people with an eating disorder, diabetes on medication or kidney disease: ask a doctor or registered dietitian.