Calorie Calculator for Weight Management

This calorie calculator helps you reach and maintain your weight loss or weight gain goal in a realistic time frame. It shows you how many calories you should eat each day and your macronutrient breakdown to achieve your desired weight. This tool is for individuals 18 years or older who are not pregnant or breastfeeding.

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 unsure of your physical activity level, start with the default - the worst-case scenario. Enter a time frame for your goal weight (start date and target date).

This weight loss calculator provides results only if it determines that your daily food energy intake needs to exceed 1,000 calories to reach your goal weight by your target date. Suppose it calculates that you need fewer than 1,000 calories. In that case, it will adjust your target date to ensure you consume at least 1,200 calories per day for women and 1,500 calories for men. Nutrition therapists recommend not going below these levels, as doing so can prevent you from meeting essential food group and nutrient requirements. You can adjust your target date later if you wish to modify your required calorie intake. If you plan to consume fewer than 1,000 calories (or 4,200 kJ) daily, please consult a doctor for guidance and support.

Body Dynamics of Weight Change

Your body needs energy to stay alive and do physical activities. The primary energy source comes from glucose, which is blood sugar from the food you eat. When your body has more glucose than it needs for energy, it sends the extra to the liver and muscles to be stored as glycogen for later use. However, there is a limit to how much glycogen the liver and muscles can hold. Once they are full, any leftover glucose is turned into triglycerides and stored in fat cells.

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 fat along with some lean tissue in 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, followers of diet programs based on this simple rule of thumb usually fail to reach their weight loss goal in the long run.

Calculation of Calorie Requirements

This calculator uses the mathematical body model equations developed by Kevin Dennis Hall, Ph. D., and his team of researchers at the National Institute of Diabetes and Digestive Kidney Diseases of the National Institute of Health. It has been shown that his mathematical model can accurately determine 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 Institutes 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.