Calorie Deficit Calculator

A calorie deficit is when the calories consumed are less than the calories expended by the body. In this state, the body draws on stored energy, mainly fat, to make up for the shortfall, leading to weight loss. Regardless of diet type, this deficit is the common element.

This calculator turns this concept into a plan. It first estimates your daily calorie expenditure, then subtracts the chosen caloric deficit to calculate your daily calorie goal. If you enter a target weight, it can also estimate how long it would take at that rate to reach that weight.

What is a calorie deficit?

The body burns energy even when it is at rest. The sum of all calories burned per day is the total daily energy expenditure (TDEE), and this is the amount of calories required to maintain weight. If that amount of calories are consumed, then weight remains stable.

When intake is less than the TDEE (Total Daily Energy Expenditure), a calorie deficit exists. When you eat 500 calories less per day than your TDEE, your body will burn fat and muscle to make up for that shortfall, which leads to weight loss. The larger the daily deficit, the faster the weight loss.

How many calories does it take to lose a pound of weight?

One pound of body fat contains about 3,500 calories and one kilogram contains about 7,700 calories. When spread out over a week, this equates to 500 calories per day. This is why a daily calorie deficit of around 500 calories is often considered the typical goal for losing approximately one pound of body weight each week.

A daily calorie deficit of 250 calories is moderate and the goal would be to lose about a half pound per week. A daily calorie deficit of 1,000 calories is very aggressive with the goal being to lose two pounds per week but this is difficult to maintain and often results in loss of muscle mass. The following table shows some common options for better comparison.

The 3500 calorie rule should be considered a rough guideline and not an absolute law. It assumes that every pound lost is pure fat and that metabolism never changes, which isn't true in the long term. Actual weight loss will be slightly slower than the arithmetic estimate, as explained in the next section.

This is how this calculation tool works:

First the Basal Metabolic Rate (BMR) is calculated using weight, height, age and gender. This is the amount of energy your body needs at rest. The BMR is then multiplied by an activity factor to determine how many calories are needed to maintain weight, after which a calorie deficit is chosen to be subtracted from this figure to obtain a daily target.

Enter your detailed information and select a weight loss rate. A prominent place on the page will show you how many calories to consume daily if you want to lose weight at that rate, along with your calorie needs for weight maintenance and calorie deficit. If you enter your goal weight, you can also see the total amount of weight you need to lose as well as the estimated number of weeks it would take.

The formula for Basal Metabolic Rate (BMR)

Basal Metabolic Rate makes up the largest part of daily calorie expenditure, so we'll start with estimating it here. This calculator uses three known formulas. For people with average body build, results from these three formulas are very similar.

Mifflin-St. Jeor (recommended)

This formula was published in 1990 and is the one preferred by most nutritionists today as it reflects current knowledge of people's physical condition. It requires body weight, height, age and gender to calculate.

In this formula "w" is weight in kilograms, "h" is height in centimeters and "a" is age in years. For a man aged 30 with a weight of 80 kg and a height of 180 cm the BMR would be about 1,780 calories.

Revised Harris-Benedict Formula

The Harris-Benedict formula was introduced in 1919 and revised in 1984. It is a classic formula which calculates values that are slightly higher than the Mifflin-St Jeor Formula for many people.

The Katch-McArdle Formula

This formula uses lean body weight instead of total weight and so can be most accurate if you know your own body fat percentage. As it is based on lean body weight, it does not take gender into account.

The lean body weight is calculated by multiplying the weight by the result of 1 minus the percentage of body fat. For a weight of 80kg and a body fat percentage of 20 percent, the lean body weight would be 64kg and the basal metabolic rate (BMR) would be about 1752 calories.

Activity level

The activity factor increases the basic consumption according to training and movement. Please choose honestly as most people overestimate their activity level which leads to a higher target calorie requirement, thus weight loss gets stuck.

How low can calorie intake be?

A large calorie deficit is not always better. If you cut too much, you will lose more muscle mass as well as fat, feel worse and are more likely to give up. There's a lower limit that you should stick to.

Most guidelines say that women should not eat less than about 1200 calories a day without medical supervision, while men should not eat less than about 1500. This is because it becomes difficult to get enough nutrients at these levels. This tool helps you stay within those lower limits and will warn if you are approaching them so that you can slow down gradually rather than going too hard and then having to take a break.

Why changes on the scales are slower than mathematical calculations

The simple 3500 calorie rule assumes that your metabolism doesn't change, which is not true in reality. When you lose weight, you have less mass to transport around so your daily expenditure will slightly decrease and the rate of weight loss will gradually slow down with the same caloric deficit. This is normal and does not mean failure.

The body also adapts to reduced food intake by lowering energy expenditure. This process is sometimes referred to as metabolic adaptation. As a result, actual weight loss does not follow a straight downward line but rather a curved and flat one, often leading to longer plateaus. Since this tool predicts the best-case scenario with linear decrease, it can be expected that the actual progress will be somewhat slower than predicted.

How to protect your muscles while losing weight.

While a calorie deficit will reduce fat it can also lead to muscle loss. If you weigh the same but have less muscle your metabolism will slow down and your figure will appear flabbier. Here are two tips that may help avoid this:

Make sure you're getting enough protein. This will help maintain muscle while in a calorie deficit and promote satiety. For this reason, high-protein diets are so popular for fat loss. Stay active and exercise including strength training to give your body a reason to keep the existing muscle mass. If you enable macronutrient options, you can see the gram amounts of protein, carbs, and fats included in your goals.

Tips to keep going:

Don't weigh yourself every day but once a week in the same way. Fluctuations in water content can hide actual fat loss over a week or more and daily values are often too irregular to be meaningful. Judge your progress by trends over two to three weeks.

Choose a pace that you can actually maintain. A slow deficit over several months is better than an aggressive method that you give up on after two weeks. Recalculate your numbers regularly as you lose some weight. As your BMR goes down when you get lighter, yesterday's goal becomes today's baseline.

This calculator is for educational purposes only and does not constitute medical or nutritional advice. The values given for calories and metabolism are estimates and do not replace the judgment of a qualified professional. Consult your doctor or nutritionist before making major changes to your diet. This is especially important if you have any health problems, are pregnant, or are under 18 years old.