FatCalc

Calorie Deficit Calculator for Weight Loss

Use this calorie deficit calculator to discover how much weight is realistic for you to lose and the calories needed to achieve that weight loss. Enter your body details and a goal weight. The calculator will generate tables and graphs showing daily calorie intakes and estimated times to reach your goal weight.

Calorie intakes are shown in descending units of 50 calories. For each unit decrease, you can see how much sooner it would take to reach your goal weight. You can then choose a calorie intake level that you think is doable and try to stick to it for that period of time.

Calorie Deficit Calculator

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Enter your body parameters and a goal weight. Click the Physical Activity field to find your physical activity level. Typical physical activity level numbers range from 1.4 (sedentary) to 2.3 (very active). The default is 1.4.

What is a calorie deficit?

A calorie deficit is created when you intake less food energy than your body requires. In that state, your body draws on your fat stores to burn the extra energy it needs, resulting in weight loss.

You need energy to support your body’s autonomic systems such as breathing, digestion, the nervous system, circulation and regulation of body temperature. Energy is also required in performing daily physical activities. The more physical activities performed, such as through work or exercise, the more energy your body requires.

Through a combination of increased physical activity and reduction in energy intake, a calorie deficit will be ensured.

How do you calculate a calorie deficit?

Your calorie deficit is the energy your body requires to maintain your current weight, minus your dietary calorie intake. So for example, if your body requires 2,000 calories a day and you only feed it 1,200 calories a day, you are in a 800 calorie deficit.

Do you lose a pound a week with a 500 calorie deficit?

It is a myth that by eating 500 fewer calories a day, you will slowly lose 1 pound of weight a week. This amounts to 3,500 fewer calories a week (7 days times 500 calories) and is sometimes referred to as the 3,500 calories per pound rule. It is based on the fact that body fat contains approximately 3,500 calories of energy per pound.

Unfortunately, the rule does not take into account important contributing factors such as the physiological changes that occur during weight loss. The amounts of body fat and muscle tissue both change with an energy imbalance. When you reduce your energy intake, muscle mass is lost along with fat mass. As you lose weight, so does your body's ability to burn calories.

Formulas incorporated into this online calculator are instead based on a mathematical model developed by Kevin Dennis Hall, Ph. D., and a team of researchers at the National Institute of Health. The model is much more accurate in predicting weight loss because it factors in the body dynamics and physiological changes that occur when the body is in a calorie deficit state. These factors include changes in body fat and lean body mass, levels of glycogen, sodium, extracellular fluids, and the thermic effects of feeding.

To illustrate, if you are a 37 year old, 6 foot sedentary male weighing 265 pounds, your body burns around 2,600 calories a day and you need to intake that same amount of food energy to maintain your weight. Say you then go on a 1,600 calorie a day diet, a 1000 calorie deficit, to try and lose 85 pounds for a healthy BMI. You would be eating 7,000 less calories a week. According to the 3,500 calories per pound rule, you would lose (7000 / 3500) or 2 pounds a week and expect to lose 85 pounds after (85 / 2) or about 43 weeks. If we instead applied Hall’s mathematical model, it would show that it actually takes almost 70 weeks for that same weight loss.

Body weight loss through caloric restriction does not continue downwards indefinitely in a linear fashion as the 3,500 calories per pound rule would suggest. Rather, the loss levels off in a nonlinear fashion because of body dynamics. The actual weight loss curve is much more closely approximated by the Hall’s model.

How low of a calorie deficit should I go?

As a general rule, women should not eat less than 1,200 calories a day and men not less then 1,500 calories a day. Nutrition therapist will tell you that food group targets and nutrient recommendations will not be met below those levels.

Eating too few calories will make weight loss slower and more difficult by slowing your metabolism. Your body will sense that food is in short supply and will slow down your metabolic rate to try and protect it from starvation. This occurs even if you are overweight and deliberately trying to lose weight. The slower the metabolic rate, the slower the calorie burn.

Total Energy Expenditure and Resting Metabolic Rate

Your Total Daily Energy Expenditure (TDEE) and Resting Metabolic Rate (RMR) are also calculated. TDEE (total daily energy expenditure) is the total amount of energy your body burns daily and is equivalent to the amount needed to maintain your current body weight. Eat less than that amount and you will lose weight. Your RMR (resting metabolic rate) is the amount of energy your body burns while at rest. RMR is factored into TDEE.

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References

  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: October 20, 2021 18:18 UTC