Calorie Calculator to Lose, Maintain or Gain Weight

Use this calorie calculator to estimate the daily calories and macronutrients you need to lose or gain weight by a realistic target date, or to maintain your current weight. It uses a research-backed model from the National Institutes of Health that accounts for how your metabolism and body composition change as you lose or gain weight, giving you a more accurate and sustainable plan.

Choose whether you want to lose, maintain or gain weight, then enter your age, sex, height and weight. Choose Maintain to get the calories that keep your weight where it is, along with a quick table of the calories for losing or gaining at a steady weekly rate. Choose Lose or Gain to plan for a 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.

For Lose or Gain, enter your goal weight and a time frame to reach it (start date and target date). Your start weight is what you weigh on the start date. To see how far you should have come since an earlier date, set the start date to that date and enter what you weighed then. Note that this tool is intended for individuals who are 18 years or older and are not pregnant or breastfeeding.

This 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.

For weight gain, it will not plan an intake above 2 times your maintenance calories, and moves your target date later if your goal would need more. It also asks you to check your entries if your height and weight put your BMI below 12 or above 80.

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. In a two-year calorie restriction trial of 140 people, the changes in calorie intake the model worked out from each person's weight matched the changes measured by laboratory methods to within 40 calories a day on average, although any one person's results can differ. 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.

Your Maintenance Calories

Your maintenance calories are the daily intake that matches the energy your body uses, so your weight stays where it is. This is your total daily energy expenditure (TDEE). The calculator starts from your resting metabolic rate, estimated with the Mifflin-St Jeor equation from your height, weight, age and sex, and scales it by your physical activity level.

Maintenance is not a fixed number. A smaller body burns less energy, both at rest and when it moves, so the intake that maintains your weight goes down as you lose weight and up as you gain. That is why a plan to lose or gain weight also gives you the calories to maintain your goal weight once you reach it, which are usually different from the calories that maintain your weight today.

Calculation of Macronutrients

The calculator will calculate your macronutrient requirements (carbs, protein, and fat) in grams based on your daily calorie target with a balanced, low-fat, lower-carb, and high-protein diet. According to the Dietary Reference Intakes set by the Food and Nutrition Board of the Institute of Medicine (IOM), the 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.