How To Calculate A Calorie Deficit: The Sustainable Way To Achieve Fat Loss


When it comes to losing weight and burning fat the key to success is nothing more than using a ‘calories in vs calories out’ approach. In order to achieve weight loss you need to be in a calorie deficit, and if you can do this consistently over time then you will see noticeable results.

Achieving a calorie deficit is actually relatively simple but can seem a lot more complicated than it really is. The basic idea is that if you want to lose weight, you need to eat fewer calories than your body burns. That’s really it. Any diet that works, works by putting your body into calorie deficit. It gets a little more complicated when you start thinking about what your calorie deficit should be, how to calculate a calorie deficit, and how to achieve a calorie deficit healthily and sustainably without sacrificing any muscle goals you may have. Thankfully, however, I’m going to run you through all that as simply as I can, below.

How Does Your Body Burn Calories?

Your body burns calories in three main ways:

1. Resting metabolic rate. These are the calories your body uses just through keeping you alive. The number of calories you use at rest will vary by your body composition. Larger people use more calories than smaller people.

2. Active energy. These are the calories you burn whenever you do anything that isn’t staying completely still. So active energy includes taking part in exercise, but it also includes doing the housework and even fidgeting.

3. Thermic effect of food. Whenever you eat something, your body needs to use calories for digestion, so you will get a boost of calorie burning whenever you eat. Some people choose to eat little and often, rather than having a few big meals a day, for this reason.

What Affects The Amount Of Calories You Can Burn In A Day?

The amount of calories you burn in a day is dependent on factors such as your age, sex, body composition (e.g. your weight and your height), and how active your lifestyle is.

1. Sex – men tend to burn more calories than women. This is because men tend to have more muscle and less fat, and muscle burns more calories per pound than fat does.

2. Body composition – people who are larger (taller or heavier) have a higher resting metabolic weight than people who are smaller, so they tend to burn more calories per day.

3. Lifestyle – you can use the level of activity you have in your lifestyle to categorise your overall daily calorie burn by using it as a multiplier of your resting metabolic rate, as below:

  • Sedentary lifestyle – (office job, no exercise) – resting metabolic rate x 1.2
  • Lightly active – (office job, light exercise 3 times a week) – resting metabolic rate x 1.5
  • Moderately active – (labour-intensive job, light exercise 3 times a week) – resting metabolic rate x 1.8
  • Vigorously active – (very labour-intensive job, moderate-vigorous exercise 3 times a week) – resting metabolic rate x 2.2

How To Calculate A Calorie Deficit

A-calculator-pad-and-blue-pen-resting-on-green-foliageThe good news is that you don’t need to do all the hard work of calculating your calorie deficit yourself, There are lots of calculators online that can do it all for you. One of these is the TDEE calculator.

When you first click on the calculator, it will ask you to put in your age, sex, height, weight, and your level of activity (for all the reasons listed above). It then calculates what your maintenance calories should be. In other words, it gives you the number of calories you would need to eat each day to stay exactly the weight you are now. This is really useful because it gives you a starting point to find out where you are.

Now if you want to lose fat without losing muscle mass, you should try to avoid cutting your maintenance calories by any more than between 300-500 calories a day. Going on a crash diet with a much larger calorie deficit than this means you then run the risk of losing muscle as well as fat, which will undo all your hard work.

So once you have a figure for your maintenance calories, subtract between 300-500 calories from this amount to give you a ball park figure of the total daily calories you should aim to consume each day to push your body into a calorie deficit. I recommend starting at the lower end of this, i.e. subtract 300 – 350 calories initially and see how you go, then if your weight and fat loss slows, or you start to plateau, you can increase the deficit slowly – giving you somewhere to go – to keep the fat loss coming.

To help the process, and to ensure you remain on-track, keep up with your regular training/exercise in a sustainable way (don’t overexert yourself and make sure to take rest days). Also, make sure you stay on top of your macronutrients to ensure that you have the right amount of protein, carbohydrates, and fats. Even if you are restricting your calories, you still need to maintain the right macronutrient profile. Another great feature of this site is that it also gives you your ideal body weight, what your BMI is, and it gives you your macronutrient profile based on whether you are trying to maintain your body fat, cut it (it takes away 500 calories for this), or if you’re bulking (it adds 500 calories for this). This section will give you a good idea of how much of each type of food you should be eating for your diet to be healthy and sustainable, and to ensure you don’t lose muscle while dieting.

Keep Track Of Your Calories

To keep track on how many calories you are eating over the course of the day there are, again, plenty of apps out there.

One popular and widely used app is MyFitnessPal. This is free to download on Android and IOS and allows you to type in everything you eat, as you eat it, and it will keep track of how many calories you have eaten that day. You can set your calorie limit to whatever you want it to be, so you could set it to your calorie deficit. Then you can make sure that you don’t go over what you need.

You can also make sure that you’re not eating too few calories. As I mentioned earlier, it’s important to not make your calorie deficit too large which is easy to do if you’re not tracking the number of calories you are eating. MyFitnessPal will also keep track of your macronutrients and will warn you if you’ve gone over the recommended levels of any one key nutrient, as well as tell you if you’re not eating enough of it.

Ready, Calculate, Go!

And that’s all the tools you really need if you want to effectively calculate a calorie deficit and track the number of calories you are eating each day. Having this knowledge in your back pocket will make sticking to a healthy fat-loss diet much easier to do, and will make sure that you stay on-track to hit your goal weight through fat loss alone without sacrificing any hard-earned muscle.


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