Skip to Content

What’s a calorie deficit, and why does it matter?

If you’re reading this, I’m going to go out on a limb and assume you’ve heard someone talking about a calorie deficit diet for weight loss, but you can’t seem to make sense of the topic.

Don’t worry, I’m here to help! A calorie deficit, or a caloric deficit (you’ll see both used interchangeably) is actually a very simple concept.

We’re going to break down calories as a whole to really help you understand the idea of a calorie deficit. But, in short, a calorie deficit means that your body is burning more calories than you are consuming.

So, at the end of the day, your body is in a deficit, essentially meaning it has fewer calories than it needs.

Don’t worry if you’re still not totally clear on the topic. We’re going to break it down for you so you can be an expert on the topic.


What is a calorie and why do you count them?

The dictionary definition of a Calorie is “the amount of heat required at a pressure of one atmosphere to raise the temperature of one gram of water one degree Celsius”.

That’s a whole bunch of complicated science talk, so let’s simplify it. A Calorie is a unit of energy, and our bodies need energy to function.

Before we go any further, I should note that a dietary “Calorie” (like you see on a food label) is actually equal to 1,000 “calories”. The word “calories” (with a lowercase C) refers to a very tiny unit of measurement, so the Calorie, or kCal, you’re used to seeing is made up of 1,000 calories to make the math easier.

It’s a really silly and confusing setup that should have been changed a long time ago, but the science folks decided that simply capitalizing one letter would be enough to differentiate the two.

Nonetheless, for our purposes, we’re going to use them interchangeably, since most people do that anyway.

Confused? Don’t be. All you need to know is that calories = Calories = kilocalories = kCals. They’ll all be used interchangeably!

Counting calories is simply a way of measuring your energy intake. You’ll want to count calories if you have specific weight goals (like fat loss or building muscle mass) but we’ll get more into that below.


How do you calculate your calories?

Online calorie calculators can be very unreliable, with recommendations all over the map.

That is why I wanted to put together my own!

I’ve turned my own recommendations that I always give into a handy little calculator- it’s not just going to spit out numbers for you, it will actually explain why I recommend what I do!

Even if you aren’t quite ready to start calorie counting, knowing your maintenance calories and preferred macro (macronutrients) targets can be hugely beneficial.

Head over to this link to use my FREE Calorie & Macro Calculator to calculator your own calorie needs.

This isn’t necessarily a weight loss calculator, but I’ll give you the tools you need to succeed.


Are all calories the same?

In short: yes.

I’m sure you’ve heard someone say something along the lines of “all calories are not equal.”

Many will argue that “100 calories from fruit is not the same as 100 calories from candy.”

That argument is valid, to an extent, but not for the reasons intended.

Is 100 calories worth of fruit healthier than eating 100 calories worth of candy? Most certainly. These foods are made up of different ingredients, contain different vitamins, and have different effects on your body.

We can agree that the foods are not the same in terms of their overall health impact, but that doesn’t address the original point in question: the 100 calories is still 100 calories, regardless of where it comes from.

A calorie is simply a unit of measurement. Your body doesn’t know the difference between a calorie from a tomato and a calorie from chocolate.

Have you heard the age-old riddle, “which weighs more: 1,000 pounds of lead, or 1,000 pounds of feathers?” This trick question is set up to make you believe that obviously, the lead weighs more, but when you look closer, you realize that they are both 1,000 pounds.

Even though lead is heavier than feathers, if you have 1,000 pounds of both, they weigh the same.

The same is true for calories. No matter what the food is, 100 calories is still 100 calories. Much like a pound is a pound, or an inch is an inch, a calorie is always going to be a calorie. It’s the macronutrients of food (the protein, fat, and carbs) that will determine how different they truly are. A food containing 20g of protein is much different than a food containing just 2g of protein, but that has nothing to do with the calories.

When you break it down, a calorie will always be a calorie. Much like an inch will always be an inch, or a pound will always be a pound. It’s simply one unit of measurement.


What is calories in vs calories out?

Managing your weight can be best visualized using a scale.

On one side, you have your calorie intake, or your energy in. On the other side, you have your calories burned, or your energy out. This is your energy balance, and it’s the most important concept you’ll come across here.

Calories in vs calories out is going to be the core principle of ANY diet you follow. No matter what fad diets pop up, they follow this very basic idea.

“Calories in” refers to calories you consume from food, and calories out are all the calories you burn.

If your calories consumed are equal to your calorie expenditure, you’ll maintain your weight. If you consistently consume more calories than you burn, you will gain weight. If you consistently burn more calories than you consume, you will lose weight.

It’s truly that simple.

You may be wondering, “if it’s that simple, why is fat loss so difficult?”

Just because something is simple, it doesn’t mean it is easy.

For many, consistently eating less calories than they are burning is not an easy thing to do. As an example, let’s say that if you eat 2,200 calories every single day, you’ll maintain your current weight. If you were to bump your caloric intake up to 2,500 calories every single day, you would be in a caloric surplus of 300 calories.

When you’re in a surplus, your body has to do something with the excess calories, so they get stored.

If muscle building is the goal, you can use these excess calories to your benefit to help build muscle. But if your goal is not muscle building, these excess calories are where unwanted weight gain comes from.

A calorie deficit is the opposite. If you were to eat 2,000 calories every day on a low calorie diet, you’d be in a caloric deficit of 200 calories. And being in a calorie deficit, as we’re exploring here, is the basis of any diet.

But “calories in vs calories out” doesn’t just mean “move more, eat less” as I’ve seen WAY too many times. That is actually terrible advice.

No, it is not quite as simple as adding in more exercise. Your TDEE (total daily energy expenditure) is comprised of much more than just exercise. Your burn calories from:

  1. Your BMR (basal metabolic rate)
  2. Physical activity
  3. Non-exercise activity thermogenesis (NEAT)
  4. Thermic effect of food

We dive more into those topics in my post about TDEE, but just note that “calories out” goes way beyond exercise!


How much of a calorie deficit do you need to lose weight?

You have probably heard the notion that 3,500 calories equals one pound of fat.

According to this theory, if you cut 500 calories per day, you’ll lose one pound per week. At the end of the year, you will have lost 52 pounds.

Sounds great, right? This certainly makes sense on the surface, and based on the prevalence of this rule, it seems it must be true. I mean, according to Today’s Dietitian, the 3,500 calorie rule is cited in more than 35,000 educational weight-loss sites (and counting), so there must be some credibility to it.

Why is this believed to be the case? For that answer, we need to go all the way back to 1958, where researcher Max Wishnofsky made the calculation that a pound of fat stores about 3,500 calories. It made sense, so it stuck, and it was never really questioned too much after that, even after over 60 years.

I’m not here to poo-poo on this rule. As a general starting point, it’s just fine. In the short term, adhering to this 3,500 calorie rule can absolutely work.

But we’ve learned a ton about nutrition over the past 60 years, and it’s easy to see the serious pitfalls to this so-called rule, especially over the long-term.

This rule leads a person to believe that weight loss is as simple as 500 calories and done. If you normally eat 2,000 calories per day, you can eat 1,500 calories and lose 52 pounds after a year. I think we can all agree that it is not that easy.

For starters, this rule does not take into account the many factors that affect your caloric needs: gender, muscle mass, physical activity levels, body fat percentage, metabolic rate, and so many more.

More importantly, it doesn’t account for changes in your energy balance (your metabolism) over time.

If you were to follow this rule, you would expect to lose 52 pounds in a year. When that number inevitably stalls and you don’t hit that number, you’re setting yourself up for disappointment.

This is because healthy weight loss is not linear. In other words, you’re not going to lose weight at a consistent rate over time.

When you first begin, the 500 calories might work great. Maybe you lose a pound per week for one month straight. After that month, you start losing one pound every 2 weeks. In the third month, you’re not losing any weight at all.

You see, our bodies don’t want to be in a caloric deficit. By definition, being in a deficit means that we are consuming less calories than our bodies need. Our bodies want to maintain our weight to not become underweight, so they’re going to try to be as efficient as possible at all times.

In other words, your metabolism is going to slow down to reduce your energy expenditure (this is known as metabolic adaptation). Your body doesn’t want to lose weight!

So how do you calculate your calorie deficit? By finding your maintenance calories (check out my calorie calculator if needed) and then reducing your calories very slowly!

We won’t get too into the topic of adjusting calories as I have an entire post dedicated to it (and please, seek out a coach if this is all overwhelming for you) but I prefer to lower my maintenance calories by 200 to start. In other words, I start with a 200 calorie caloric deficit.

After a month, I’ll drop my calories by another 100-200 calories if weight loss begins to stall consistently. I like to take it super slowly, so I stay on the lower end, but upwards of 200 calories per month can work great depending on where you’re at.

Continue at this level for another month, and then repeat if needed. If you’re making incredible progress throughout the month, there is no need to make any adjustments. You will only need to make an adjustment if your weight stalls or slows for a couple weeks.

Remember, our weight can fluctuate by 5+ pounds day-to-day, so it’s important to look at the long-term trend.

Your weight may not be as low from one week to the next, but if it’s trending downward over the course of the month, you’re doing great!


Will a caloric deficit slow your metabolism?

Yes, but not to the level of “starvation mode” that you may have heard mentioned before.

Let’s say that your maintenance calorie level is 2,500 calories. You decide to eat 2,200 calories, and you’re making great progress. But after 3 weeks of no progress at all, it becomes clear that your body has adapted to the 2,200 calories.

Your metabolism has slowed, and that is now that is your maintenance level at your new, lower body weight. When this happens, you drop your calories a bit more to put yourself back into a deficit. In this example, you’d drop your calories to 2,000-2,100 calories to begin to see results again.

Your body (and your metabolism) will continue to do this to a certain point. There becomes a point when your metabolism simply cannot slow anymore, though.

The majority of your calories burned in a day are from your body carrying out basic life functions, so there is always going to be a fair amount of calories you need to consume to just continue functioning at a high level.

This number is different for everybody, and there are not hard-set rules for when this point is. But if you were to drop your calories too low, that’s when you’ll begin feeling terrible (if you do think your calories might be too low, please contact a professional).

This is when a “reverse diet” comes into play, which helps you to not only repair your metabolism, but bring your maintenance calories back up to higher numbers.


In a calorie deficit but not losing weight?

Are you in a calorie deficit and not seeing any fat loss?

There’s a very good chance you are not actually in a calorie deficit.

You certainly don’t need to track your food to have a successful weight loss journey, but if you do choose to track your calories, you need to make sure you do it correctly.

It might feel like measuring out your food portions or tracking calories in something as silly as oil you cook with is pointless, but as you can see in this graphic, these extra calories can add up quickly.

On their own, these additions seem like nothing. But over the course of the day, these small things add over 400 calories to your diet.

Maybe you don’t count the 2 packets of sugar in your coffee. I mean, it’s only 30 calories after all. On its own, that is likely not going to affect you- but combine that with the missed tablespoon of butter with your baked potato, or the olive oil used to sauté your broccoli, and these things can really start to add up.

Without measuring out your portions, it can be very easy to miss calories. Take almonds for example- a portion is going to run you 170 calories, but if you don’t measure out a portion, you can very easily have an extra half of a serving, adding an extra 85 calories that are unaccounted for.

It may be a pain in the butt to track each thing, but if you swear you are in a caloric deficit and the weight loss results are not coming (or you are seeing some weight gain), it might be useful to dive in and make sure everything is accounted for.

There’s a good chance you are missing calories in your day!

Don’t get me wrong- you don’t have to track every little thing. But if you’re struggling with your weight loss, making sure you are tracking your calorie intake correctly is a great place to start.


Will overeating ruin a calorie deficit?

One day of overeating does NOT offset all of your progress. I promise.

When you’re dieting, it’s easy to feel like you ruined your progress after a Friday or Saturday night full of pizza and ice cream. But that doesn’t have to be the case.

Let’s walk through this example so you can see exactly what I mean…

For these purposes, let’s assume you find out that your maintenance calories are 2,200 per day. In other words, if you eat that many calories every day, you will maintain your current weight.

You decide you want to shed some body fat and lose weight, so you set a calorie goal of 1,800 calories every day (a deficit of 400 calories every day).

There are many different ways to adjust your calories, so this is just a random example of 400 calories per day. Obviously, you would adjust based on your own preferences and goal weight!

Your diet is going great, you’re seeing results, and you’re eating right around 1,800 calories every day. You’re feeling great and really thrilled with your progress.

But then…Saturday happens.

By the end of the night, after all of the drinks, pizza, and dessert, you end up eating 3,200 calories total, which is well over your calorie goal. In fact, it’s nearly double your target calorie intake of 1,800 calories.

It’s easy to feel like you messed up and that you ruined all of your progress. I mean, your goal is a caloric deficit, and 3,200 calories is well above your maintenance calories. You were doing great all week, but now one day of overeating might have destroyed all of that…

Take a step back and look at the big picture.

It’s important to look at the week as a whole, not just the single day. Even though you overate on this one day, you are still in an overall caloric deficit for the entire week.

Most people get too caught up on a single day, when in reality, our bodies don’t reset overnight. If you overeat on a Saturday, it’s not like your body is starting back over at 0 calories on Sunday.

For simplicity’s sake, it’s easiest for us to track daily calories and take things on a day-by-day basis. But it’s extremely important to be able to step back and look at the larger picture.

Just because you overate on a single day, you may very well still be in an overall deficit over the span of the week.

Is the calorie deficit as large as you planned? No. In fact, it’s half of what it would have been if you hadn’t overeaten on Saturday. But you did, and that is TOTALLY FINE.

A deficit is still a deficit. Progress is still progress. One day does not make you a failure.

If you look at the big picture of the whole week, it wasn’t a failure at all. You still achieved an overall deficit, which was the goal.

When you look at it through that lens, you still succeeded.

Whether you overeat (or undereat) by 200 calories or 2,000 calories, it’s only one day. One day is never going to make or break your progress!

You can remain perfectly on track regardless of what a single day does, or doesn’t do.

Small progress is still progress.


Share The Love

About Matt Rosenman

With over 15 years of experience in health and fitness, Matt Rosenman is the expert voice behind Matt’s philosophy is simple: no foods are off-limits, and a healthy lifestyle shouldn't be complicated or restrictive. As a former certified personal trainer with a bachelor’s degree in Health Behavioral Sciences, Matt brings well-rounded expertise to his blog. From revamping classic recipes with a nutritious twist to breaking down fast food menus, his goal is make healthy living less confusing for everyone. Featured in major publications and with a strong following on social media, Matt is committed to making “healthy” uncomplicated—no matter where you are in your health journey. Join Matt on his mission to simplify health without sacrificing flavor. Learn More