Methodology and Data Sources

Our principles

We build calculators that show their work. That means three commitments. First, we use established formulas from the scientific and clinical literature, not invented shortcuts. Second, we tell you which formula produced your result and, where relevant, why. Third, we never trade safety for engagement: our weight-loss tools refuse to recommend calorie targets below widely accepted floors. These tools are educational and do not replace advice from a qualified health professional. See our disclaimer for the full statement.

Basal metabolic rate

We estimate basal metabolic rate, the energy your body uses at rest, with the Mifflin-St Jeor equation (Mifflin et al., 1990), which research consistently finds to be the most accurate general predictor for healthy adults.

• Men: BMR = (10 x weight in kg) + (6.25 x height in cm) minus (5 x age) plus 5
• Women: BMR = (10 x weight in kg) + (6.25 x height in cm) minus (5 x age) minus 161

When you provide a body fat percentage, we switch to the Katch-McArdle equation, which is based on lean body mass and can be more accurate for lean or muscular people:

• BMR = 370 + (21.6 x lean body mass in kg)
• Lean body mass = weight x (1 minus body fat percentage divided by 100)

The Target Panel always names which of the two formulas produced your number.

Total daily energy expenditure

To turn basal metabolic rate into total daily energy expenditure, we multiply by a standard physical activity factor:

Energy and weight change

To convert calories into weight, we use the widely used estimate that one kilogram of body mass holds about 7700 calories, which is close to 3500 calories per pound. A daily deficit or surplus is multiplied by seven for a weekly figure and divided by 7700 to project weekly weight change. This is a planning estimate; real change is affected by water balance, adherence, and metabolic adaptation, so we always describe projected dates as estimates.

Safety floors

Our calorie deficit, calorie cycling, macro, keto, and body recomposition tools never output a calorie target below 1200 calories for women or 1500 calories for men. Below these levels it becomes very difficult to meet protein, vitamin, and mineral needs, and lower intakes do not improve long term outcomes. When a requested deficit would cross the floor, we cap the target and tell you.

Macronutrients and protein

Our macro calculator sets protein first, from body weight, using 1.6 to 2.2 grams per kilogram depending on goal, then sets fat from the preset but never below a floor of 0.6 grams per kilogram, and fills the remaining calories with carbohydrate. Energy values follow the Atwater factors: protein and carbohydrate provide 4 calories per gram, fat provides 9. The protein calculator uses goal-based ranges: about 0.8 to 1.0 g/kg for general health, 1.2 to 1.6 for general fitness, 1.6 to 2.2 for muscle gain, and 2.0 to 2.6 g/kg of lean mass when cutting.

Other formulas

• FFMI: lean mass in kg divided by height in metres squared, with a normalization of plus 6.1 times (1.8 minus height in metres). See the FFMI calculator.
• Waist to height ratio: waist divided by height in the same units, with risk bands at 0.4, 0.5, and 0.6. See the waist to height calculator.
• Calories burned walking: the MET method, calories = MET x weight in kg x hours, with walking METs of 2.8 (slow), 3.5 (easy, 2.8 mph), 4.3 (brisk, 3.5 mph), and 5.0 (fast, 4 mph) from the 2011 Compendium of Physical Activities. Steps convert to distance using a stride estimate of 0.415 times height. See the walking calculator.
• Water intake: a baseline of 30 to 40 ml per kg, plus 350 ml per 30 minutes of exercise, plus a hot-climate allowance. See the water calculator.
• Net carbs: total carbohydrate minus fiber minus half of sugar alcohols. See the keto calculator.
• Weight loss percentage: (start minus current) divided by start, times 100. See the weight loss percentage calculator.

Food data for the recipe calculator

The recipe calorie calculator uses a bundled dataset of 163 common raw ingredients drawn from USDA FoodData Central (SR Legacy and Foundation Foods), expressed per 100 grams for calories, protein, carbohydrate, fat, and fiber. Values are typical figures for raw foods, so cooking changes such as water loss are not modeled, and specific brands will vary. We weigh volume measures like cups using typical densities, but weighing in grams is always more accurate.

Update policy

We review our formulas and food data quarterly and whenever a correction is brought to our attention. If you spot an error, please tell us through the contact page and we will investigate. When we change a formula or a data value, we note it here. Our reference sources include the original Mifflin-St Jeor (1990) and Katch-McArdle publications, the 2011 Compendium of Physical Activities MET tables, USDA FoodData Central, and public health guidance on waist to height ratio and clinically meaningful weight loss of 5 to 10 percent.