Weight Loss Calculator and Planner

Use this weight loss calculator and planner to help you reach your goal weight within a realistic time frame and maintain it. Based on formulas developed by the National Institute of Health, it can determine the calories you need daily to reach your goal weight.

You can also specify an energy deficit that's workable for you and it will calculate how long it would take to reach your goal weight.

The results of the calculations will show your projected weight loss or gain in both tabular and graphical formats.

Weight Loss Calculator


Enter your body parameters and your goal weight. If you don't know your activity level, click the Estimate button for an estimation.

Select the Energy option and enter a start date and end date if your want to calculate the average daily energy intake you would need to reach your goal weight within that time frame.

Select the Time option and enter a start date and your planned daily energy intake to calculate an estimation of when your goal weight will be reached with that dietary intake.

Click Calculate and the results will be presented in tabular and graphic formats. If your goal weight is less than your current weight, the graphics view will also include a chart series of your weight projections at starvation level (0 Calories) and at 1,000 Calories per day. Consult a doctor for guidance and support if you are considering a diet of less than 1,000 Calories (4,200 kilojoules) per day. Food group targets and nutrient recommendations will not be met below that level.

What is the science behind weight loss?

A change in body weight results from the difference between your food energy intake and the amount of energy expended by your body. Energy is burned in maintaining your body functions and in performing physical activities. For successful weight loss to occur, there must be an energy imbalance such that your energy expenditure is greater than your energy intake.

About the Calculations

This calculator uses formulas developed by Kevin Hall, Ph. D., and a team of researchers at the National Institute of Health. They are much more accurate in determining energy expenditure and energy requirements for the purpose of weight management. They challenge the popular 3,500 calories per pound rule by taking into consideration the physiological changes that take place during weight loss. This includes changes in body fat, muscle mass, the thermic effects of feeding, glycogen levels and sodium intake.

Along with your sex, age and basic body measurements, the formulas requires your body fat percentage value. The calculator roughly estimates it through an equation derived from research by Jackson et al on estimating percentage body fat from body mass index.

Your resting metabolic rate (RMR) or resting energy expenditure (REE) value is also required. The terms RMR and REE are generally used interchangeably and is a measurement of the energy burned by your body to keep it functioning while at rest. Both RMR and REE are usually measured by means of indirect calorimetry gas analysis. Such measurements can be taken at health clubs and some medical clinics but can be expensive and inconvenient. This calculator roughly estimates the value for you through a predictive Mifflin-St Jeor formula based on your height, weight, age and sex.

Related Calculators


  1. Quantification of the effect of energy imbalance on bodyweight.
    Hall KD, Sacks G, Chandramohan D, Chow CC, Wang YC, Gortmaker SL, Swinburn BA.
    Lancet (2011 Aug 27) 27;378(9793):826-37.
  2. The effect of sex, age and race on estimating percentage body fat from body mass index.
    Jackson et al
    International Journal of Obesity (2002) 26, 789–796
  3. A new predictive equation for resting energy expenditure in healthy individuals.
    M D Mifflin, S T St Jeor, L A Hill, B J Scott, S A Daugherty, Y O Koh
    The American Journal of Clinical Nutrition, Volume 51, Issue 2, February 1990, Pages 241–247

Last Update: Oct 18, 2020 16:51