How many calories should I eat to lose weight? Start from your BMR

Why a one-size calorie target misses

Your body burns energy in two parts. BMR is what it uses at complete rest, for breathing, circulation, and keeping organs working. Movement and exercise add the rest, and most people burn 20% to 90% more than their BMR over a full day. A 30-year-old man who is 180 cm and 80 kg has a BMR of about 1,780 kcal, and with moderate exercise he needs about 2,759 kcal a day to keep his weight. A target copied from someone else can sit far above or below that.

Cutting too hard has its own cost. Most guidelines suggest losing 0.5 to 1 kg (1 to 2 lb) a week, because faster loss usually takes more muscle with it and is harder to keep off. Common guidance is to stay at or above 1,200 kcal a day for women and 1,500 for men unless a doctor supervises the diet.

Find your BMR, your daily need, and a target

Start with the BMR Calculator. Enter your sex, age, height, and weight, and pick a formula. Mifflin-St Jeor is the default because studies found it closest to measured resting energy for most adults. Katch-McArdle works from lean body mass and suits people who know their body fat percentage. The result lists your daily need at five activity levels, from sedentary (× 1.2) to very active (× 1.9).

Then set a goal in the Calorie Calculator. It starts from the same BMR, multiplies it by your activity level, and adjusts for the weekly change you choose, counting about 7,700 kcal per kilogram of body fat. To lose 0.5 kg a week it subtracts about 550 kcal a day, so the man above lands at 2,209 kcal. A target below 1,500 kcal for men or 1,200 kcal for women is flagged.

To see where you are heading, open the Ideal Weight Calculator. It gives your ideal weight by the Devine, Robinson, Miller, and Hamwi formulas, next to the healthy BMI range for your height. For a 180 cm man the formulas span 71.5 to 77.3 kg. None of them was built to define a perfect weight, so treat the span as a rough target.