Calculate Your Daily Calories and Macros to Reach Your Goal Weight

This calorie calculator uses a research-backed model from the National Institutes of Health to estimate the daily calories and macronutrients you need to reach your goal weight by a realistic target date. Unlike calculators based on the outdated "3,500 calories per pound" rule, it accounts for how your metabolism and body composition change as you lose or gain weight, giving you a more accurate and sustainable plan.

Enter your age, sex, height, current, and goal weight. Click the Physical Activity field to find your physical activity level. Physical activity levels can range from 1.4 (little activity) to 2.3 (very active). The default is 1.4. If you are trying to lose weight and are unsure of your physical activity level, start with the default. It gives the lowest calorie target, so it errs on the safe side.

Enter a time frame for your goal weight (start date and target date). Note that this tool is intended for individuals who are 18 years or older and are not pregnant or breastfeeding.

This weight loss calculator provides results only if it determines that your daily energy intake must exceed 1,000 calories to reach your goal weight by your target date. If the calculator determines that you need fewer than 1,000 calories, it will adjust your target date to ensure that you consume at least 1,200 calories per day for women and 1,500 calories per day for men.

Nutrition therapists recommend not going below these calorie levels, as doing so can hinder your ability to meet essential food group and nutrient requirements. If you wish to modify your required calorie intake, you can adjust your target date later. If you plan to consume fewer than the recommended amount, please consult a doctor for guidance and support.

Body Dynamics of Weight Change

Your body needs energy to stay alive and do physical activities. It burns a mix of carbohydrate and fat for that energy. Glucose, the sugar in your blood, is the brain's main fuel, while at rest much of the rest of your body runs on fat. When you eat more carbohydrate than you need, your body tops up its glycogen stores in the liver and muscles and burns more carbohydrate in place of fat. When you eat more calories than you burn overall, most of the surplus is stored as fat, mainly from the fat in your diet. Turning carbohydrate itself into fat only becomes significant with large, sustained overeating.

To lose weight, you must eat fewer calories than your body uses daily. This creates an energy deficit. When that happens, your body takes energy from its stores to meet its daily needs. This process leads to weight loss by breaking down fat and lean body mass.

A commonly held but incorrect belief about weight loss suggests that to lose 1 pound a week, you need to eat 500 fewer calories daily, which adds up to 3,500 calories fewer in a week. This idea comes from the assumption that fat tissue contains about 3,500 calories per pound, so by burning that many calories, you would lose 1 pound. However, the body doesn't operate in such a simple way. Eating 3,500 fewer calories doesn't mean your body will automatically burn 3,500 calories of fat.

The reality is that when you lose weight, you lose some lean tissue, including muscle, not just fat. Lean mass consists of everything that's not fat, including muscle, bones, organs, ligaments, tendons, other tissues, and water. The rule also ignores other body dynamics of weight loss, such as the reduction in basal metabolic rate (BMR) and decreased energy cost of physical activity. Your total daily energy expenditure (TDEE) changes with weight loss. Consequently, people following diet programs based on this simple rule of thumb lose less weight than it predicts, and the shortfall grows the longer they diet.

Calculation of Calorie Requirements

This calculator uses the mathematical body model equations developed by Kevin D. Hall, Ph.D., and his team of researchers at the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health. His mathematical model has been validated against controlled feeding studies and accurately predicts an individual's energy requirements for weight management. It challenges the popular 3,500 calories per pound rule by accounting for the body dynamics discussed earlier, including body adaptations that oppose weight change and the weight change associated with changes to glycogen and extracellular fluid levels.

Calculation of Macronutrients

The calculator will calculate your macronutrient requirements (carbs, protein, and fat) in grams based on the required caloric intake to reach your goal weight with a balanced, low-fat, low-carb, and high-protein diet. According to the Food and Nutrition Board of the Institute of Medicine (IOM) dietary guidelines, an acceptable macronutrient distribution range is 45%-65% of calories for carbohydrates, 10%-35% for protein, and 20%-35% for fat. The calculated amounts put each macro's percentage within the IOM acceptable range for the different diet types.

Knowing your macronutrient needs is important for planning meals and controlling portions. If you want to lose weight, gain weight, or keep your weight steady, understanding how many calories you need and the right balance of macronutrients can help you make better food choices and reach your goals.