Weight Loss, seems like everyone’s talking about it. You can’t turn on the TV at night without being bombarded by infomercials promising easy solutions to losing that flab. You can’t open Google without some guy promising to teach you hitherto undiscovered secrets to get a six pack.weightloss

But these easy solutions to weight loss forget to tell you one thing: there is no “easy way.” It comes down to sacrifice, discipline, and yes, sometimes pain. And for most people, a bit of basic math. Math? But don’t worry, the math part is the easiest step.

To lose weight you have to keep in mind the fundamental law of losing weight: You must be at a negative energy deficit.

I don’t care what that infomercial selling that fat-burn-annihilator-by-squeezing-your-pinky-device promised you: you’ve got to cut calories to lose weight. There is no other way. That means you need to consume less calories than your body (currently) needs to maintain its weight. This forces your body to tap into your body fat stores for energy because you are not acquiring enough calories from your diet.

But in order to find out how many calories you need to eat to lose weight, you first need to figure out how many calories you burn per day. This figure is called your “Caloric Burn Per Day”. And to figure this out, we have to do a bit of basic math.

STEP ONE: Calculating Your Caloric Burn Per Day

There are basically three components to the caloric burn:

  1. BMR (Base Metabolic Rate): Sounds complicated but it’s really quite a simple explanation. Essentially, BMR just means how many calories you burn when at complete rest. This assumes no primary physical activity. The base BMR for the average person is around 65 percent of the total calories you burn.
  2. Activity Level: How many calories you burn while moving around. This includes your day-to-day basic required activities (walking around, standing up, etc.) and any extra activities (lifting weights, cardio, training, etc.). This represents about 25 percent of the calories you burn, though this can be HIGHLY depending on your level of physical activity. For example, if you train Muay Thai, this percentage would shoot up drastically.
  3. Thermic Effect of Food (TEF): Your body requires calories to maintain the digest process of food. Basically, it takes calories to burn calories in your body. This figure only adds up to about 10 percent of the process and is pretty much irrelevant for the scope of this article.

For the scope of this article, we will cover points 1 and 2 (BMR and Activity Level) from which you can find out exactly how many calories you need to eat a day to lose weight.


First we need to calculate the BMR (Base Metabolic Rate) then Calculate the Adjusted BMR which takes into account any physical activity you do during the day. This will give us the number of calories we burn per day (Calorie Burn).

Calculating your BMR (Base Metabolic Rate):

There are a number of different formulas to calculate your BMR. For the sake of completion, I’ll give the two major ones here, but we will only use the Harris Benedict Method as it’s the easier one to use right off the bat.

Harris Benedict Method

BMR Men: = 66.5 + (6.23 X weight in pounds) + (12.7 X height in inches) – (6.8 X age)

BMR Women: = 655 + (4.35 X weight in pounds) + (4.7 X height in inches) – (4.7 X age)

The above formula is one of the most common ones you’ll see floating around on the web. It’s a good way to guesstimate your BMR with just your weight, height, and age. With this formula, you don’t need any extra tools, measuring tapes, or special equipment to calculate your BMR. However, it doesn’t take into account your body fat level which can make a difference as people with more muscle have a higher base metabolism (muscles burn more calories during the day). Basically the problem this formula is it can overestimate the caloric burn for people with higher body fat levels and underestimate it for people with lower body fat levels.

Katch & McArdle Method

BMR (Men + Women) = 370 + (21.6 * Lean Mass in kg)

Lean Mass = weight in kg – (weight in kg * body fat %)
1 kg = 2.2 pounds, so divide your weight by 2.2 to get your weight in kg

A slightly more complicated formula but one that’s more accurate than the HB method. However, the downside to this formula is that it requires you to know your approximate body fat level. If you get this figure wrong (and many people under-estimate their bodyfat levels) the accuracy goes down.

Both equations have pros and cons. But for sake of simplicity, we will go with the Harris Benedict Method. These formulas just give you a base estimate that may be a few hundred calories off the mark– you will need to modify the calories depending on your actual weight loss results. But for the beginner, they are great starting points. If you have a good idea of your body fat percentage already, I suggest you go with the KM Method instead.

Working Example of the Harris Benedict Method

We take a 35 year-old male that’s 80 kilos and 180 cm tall and plug those figures into our HB formula (for men):

BMR = 66.5 + ( 13.7 x weight in kilos ) + ( 5 x height in cm ) – ( 6.8 x age in years )

This gives us the following result: 66.5 + (13.7x 80) + (5 x 180) – (6.8×35) = 1,824 calories per day BMR

So our hypothetical man requires has a BMR of 1,824 calories.

THE PROBLEM: The problem with just the straight BMR calculation (for either HB or KA methods) is that it’s not exactly accurate if you are not lying around in bed all day.Which leads us to the next section…

Calculating Your Adjusted BMR:

Just calculating your BMR as in the above example is not enough, especially if you are physically active. Now taking into consideration that you (if you are reading this on muaythaipros.com) probably do Muay Thai or some other martial art, we need to adjust the BMR formula to take into account the calories you burn from physical exercise. Even if you do not train Muay Thai or do any sort of sports, you will still need to figure out the Adjusted BMR as you will be doing SOME physical activity during the day, even if it’s just walking and moving around.

The adjusted BMR formula is as follows:

Adjusted BMR = BMR + Estimated Exercise Calorie Expenditure (Activity Level) + Margin of Error

Let’s break this formula down into plain English with an example:

Working Example of Calculating your Adjusted BMR

Let’s take our hypothetical 170lb man used in the BMR formula above with a BMR of 1,824 calories. Our man lifts weights in the morning for an hour (roughly 300 calories burned), does a 30 minutes slow run (400 calories) and a 1.5 hour Muay Thai session (800-1000 calories). Plugging all these figures into the Adjusted BMR formula: 1824 (BMR) + 400 (30 minute run) + 1000 (1.5 Muay Thai Session) + 200 (margin of error to account for things like walking around etc.) = 3424 calories. That means our hypothetical man whose 180cm tall and 170lbs needs roughly 3424 calories per day to MAINTAIN his current weight with a 30 minute run, a 45 minute weight session, and a 1.5  hour Muay Thai class.

Calculating a Specific Activity Level:

If you don’t know the calories burned per hour of specific exercises you can check out our Average Calories Per Exercise article OR you can use the below formula chart (yes, MORE formulas, but they really are simple!)

Little to no exercise: Daily kilocalories needed = BMR x 1.2
Light exercise (1–3 days per week) Daily kilocalories needed = BMR x 1.375
Moderate exercise (3–5 days per week) Daily kilocalories needed = BMR x 1.55
Heavy exercise (6–7 days per week) Daily kilocalories needed = BMR x 1.725
Very heavy exercise (twice per day, extra heavy workouts) – I’d slot Muay Thai training in Thailand here Daily kilocalories needed = BMR x 1.9

The above formulas are useful if you don’t know the number of calories burned by the specific activities you do and just want to break your activity level into something general.

Taking into account Muay Thai training

thai clinch bangla

A two-hour Muay Thai session in Thailand, if you push it hard, might burn anywhere from 1000-1500 calories including the run most Thai gyms have students do before training. I generally estimate around 1200-1300 IF you did a run before training, but it could be more or less depending on what you are doing and how hard you are doing it. If your “training” is mostly sitting around and talking to people around you, then cut that amount in four. If you’re hitting the pads and bag like your life depended on it and filling your break periods with pushups and sit-ups, you stay for clinching and sparring, and you knee and teep the bag 200 times after training, and you do 30 minutes of skipping or a 30 minute run before the session then 1500 calories might be a solid figure.

So assuming you do ONE proper Muay Thai session and a run before the session, you might be burning 1200 or so calories in that 2 hour period. If you do two sessions a day and a morning run, add another 1000 – 1200 or so calories. That’s roughly 2000 – 25000 calories you are burning a day. Add that to your Adjusted BRM formula as the Estimated Exercise Calorie Expenditure number and you have your Adjusted BMR number with taking your training level into account.

Now assuming the two fundamental laws of nutrition:

  1. If you eat more calories than you burn, you will gain weight
  2. If you eat less calories than you burn, you will lose weight

By the #2 law, you need to adjusting your calories you intake per day into below your maintenance level (Your ABMR) to lose weight.

This is so important that we’ll say it again: After you have your Adjusted BMR, you simply figure out the caloric deficit and make sure you hit that every day to lose weight.

STEP TWO: Calculate Your Required Daily Calorie Deficit

The Adjusted BRM number gives you the number of calories you need to maintain your current weight given your current activity level. But now we need to calculate the exact deficit in calories you need to subtract from that figure so you lose weight.

The standard figure thrown around by the fitness industry is a 500 calories a day deficit. This works out to a nice neat sum of 3500 calories a week (500 x 7) which just so happens to be how many calories it takes to burn 1 pound of fat off your body. It’s a nice neat and tidy sum that works out nicely on paper. However, in reality just slapping an immediate 500 calorie deficit onto your diet may cause some problems for (some) people.

You may have some problems with this in the following cases:

Case 1: You are doing a lot of physical activity

Why? Assuming you doing a lot of physical activity – i.e. you are an athlete say — you need to give your body enough ample calories to function and repair muscle. When you are on a deficit it’s MUCH harder on your body as your body is forced to deal with repairing all the muscles from your heavy activity levels (insert whatever sport you are doing) while not having enough nutrients floating around to easily do so (must tap into your fat reserves as you are on a caloric deficit).

 You might find going on too much of a deficit, in this case, can affect your energy levels in a big way, especially if cardio makes up a big portion of your day. You may feel drained, tired, and constantly sore, not to mention moody. This can be especially true if you start to play around with the carbs, fat, and protein ratios that make up your meals (especially if you opt for a low carb or paleo style diet).

If your goal is athletic performance during the day and to improve technique (in whatever sport you are participating in), then it’s better to accept slower weight loss results for better performance. If you are cardio heavy, I would drop your deficit down to 300 or so calories a day UNLESS you are more than 20% body fat. You may not weight loss results as fast, but you will maintain more energy during the day for training.

Case 2: Your bodyweight is not very high and/or you are under 15 percent body fat

Why? It’s a fact that the leaner you are the more you might struggle with the 500 calorie number. The lighter you weight, the bigger a percentage of your caloric intake the 500 calories will become.

Health organizations recommend that adult males eat more than 1600 calories a day while adult women should eat more than 1200 calories. Of course, this is based on the average women and man and not taking into account specifics or activity levels. But it’s a good rule of thumb. Go on too much of a deficit and bad things happen.

Say you are 135lbs at 10 percent body fat. You require fewer calories than someone at 185lbs at 10 percent by the sheer fact that you are 50lbs lighter! You might need 1700 calories to keep at maintenance while someone whose 185lbs might require 2100 calories at maintenance. You can probably see here while applying a straight -500 calorie deficit for both men who do NOT weight the same, might not be a good idea.

Cut your calories by too much and your body might drop into starvation mode.  And this folks, is not a good thing. Studies have shown that your metabolic rate could drop to as much as 30-40 percent if this is the case (and your energy levels will plummet!).

It’s better to give yourself a target percentage range between 15 to 30 percent deficit with picking the lower percentage if you are doing intense cardio like Muay Thai training. You might even have to go even lower and ignore the percentage and just aim for a 300 calorie deficit (if even 15 percent is around 500). If you don’t do any cardio and only lift weights then a 500 calorie deficit may be ok. But outside of that, it’s better to go for a bit less, say 300-400 or so.

RULE OF THUMB: The leaner you are, the lower your deficit you should be (15-20 percent) while if you have a higher body fat percentage you could get away with 30 to 35 percent).

At a solid 500 calorie deficit, you may freak your body out and go into a starvation mode if you get the figure wrong. Why? If your calories are too low, you will feel lethargic, grumpy and generally won’t be in a good state of mind.

So back to our formula. Say we aim for a 15 percent deficit. Since we used the HM formula which does NOT include the body fat calculation in, let’s say our hypothetical man has a body fat of 15 percent and is an athlete (given that we calculated our man trained cardio a solid 2 hours a day and lifted weights). That means we should aim for a figure around a 15-20 percent deficit.

Working Example of Calculating the Calorie Deficit for Weight Loss

The ABRM above gave us 3300 calories. So now it’s 3300x.15 = 495 calories deficit needed (which actually works out almost exactly to our base 500 calorie deficit). So 3300 – 495 = 2805 calories per day to lose weight.

STEP THREE: Track Your Weight Loss Progress

Once you know how many calories to eat to lose weight, it’s now a matter of adjusting your diet and activity levels meet this number. As a final note, you will absolutely have to track your progress by weighing yourself at least once a week and taking measurements.

Again, it’s not enough to actually just calculate the required calories needed to lose weight. You have to actually keep track of your caloric intake, take measurements of your weight, and examine your progress. If you are not losing weight every week, you may have to re-examine what you are doing and reduce your calories by a few hundred, either by reducing what you eat, changing WHAT you eat, doing more exercise or some combination of these. The emphasis is on ADJUSTING your calories if you have to so you make progress.

It’s important to note here that when you are losing weight, you should ideally be including some form of strength training (i.e. lifting weights, usually heavy weights). While this is very taxing on your body if you are already doing quite a bit of cardio (and the assumption is that you are doing cardio like Muay Thai for weight loss), it’s essential if you want to retain your valuable muscle when you cut your weight. By including a strength training program into your “routine” you help ensure that your weight loss is mostly fat and not a combination of both fat and muscle which will certainly be the case if you are not lifting weights. Losing only fat rather than both fat AND muscle can make a substantial difference to the “look” of your body at the end of your weight loss program; losing only fat results in a more “fit” muscular look while losing fat and muscle often results in just a slimmer look. The former is almost universally preferred.

The leaner you are (especially if you are below 15 percent body fat and even more so if you are nearing the single digits), the more likely you are to lose both fat and muscle when you are on a calorie deficit which is why it’s critical you include some strength training in your workout routine. If you are not lean (higher bodyfat, say 20 percent or more), there is a lot more leeway here as it’s possible to burn mostly fat and not muscle if you are higher body fat WITHOUT doing strength training.

So there we go, that’s how to calculate the number of calories for weight loss. So is that it? Is simply ensuring your calories eaten vs calories spent remains in the negative all there is to know about how to lose weight? The short answer is, absolutely not. The long and complex answer would take a number of long and heavy articles to explain exactly why. But the short of it is that weight loss is far more complex than a simple calorie in versus calories out issue that we’ve made it out to be in this article.

For optimal fat loss results, you will really need to look at other variables such as the quality of your calories, the nutrient ratio of that make up your food (carbs, protein, and fat ratios) and your meal timing. Adding a bit of exercise on the plate as well will encourage positive metabolic changes, increased blood circulation, and other hormonal changes that can help optimize your fat loss. All these variables have been shown to have dramatic effects on your fat loss.

However, these all still play a far second fiddle to your calories in vs calories out which, at the end of the day, are the most critical and important factor in losing weight.

Our next article will talk specifically about How to Lose Weight in which we will discuss everything you need to know about losing fat while keeping muscle when you lose weight.