How Many Calories Should I Eat?

You’ve probably heard many experts, influencers, nutritionists and fitness folk talk about ‘calories in vs calories out’, put simply the calories you consume per day versus the calories you expend. It’s a very basic and uncomplicated physiological principle for weight loss, maintenance and gain, there needs to be the correct balance of calories in vs calories out. But, how do you calculate the number of calories needed per day in order to get that balance right? It’s all very well to say ‘be in a calorie deficit for weight loss’, but how does that translate into a magic number for you? There isn’t a single magic number that works for us all, we are all individual, with different shapes, sizes and lifestyles, so how do we understand what that balance should be and how many calories we should be consuming each day?

This article answers the age-old question – how many calories should I eat? In an easy-to-understand way, I explain exactly how to calculate calorie intake aligned to your goals.

How many calories should I eat - TDEE Impact (Calories out)

I recently published an article regarding ‘Metabolic Adaptation’, which I defined as “the slowing down of one’s metabolic rate (metabolism) after long-term undereating and substantial fat loss in an attempt to preserve stored energy (body fat)”. Within this article, I talk in great detail regarding Total Daily Energy Expenditure (TDEE), which is the ‘calories out’ part of our equation, and the elements that make this up. I’ll give you a quick recap as it forms the foundations of the point of discussion today.

Basal Metabolic Rate (BMR)

This is the sum of all bodily functions needed to keep the body alive. Things like breathing and the processes our organs go through each day.

Thermic Effect of Food (TEF)

The Thermic effect of food or TEF refers to the number of calories needed by your body to process the food you eat.

Exercise Activity Thermogenesis (EAT)

As you would expect, this is the sum of energy utilised for exercise of the conscious kind. So running, resistance training, HIIT etc would all fall within this category.

Non-Exercise Activity Thermogenesis (NEAT)

NEAT accounts for all your subconscious physical activity. Activities such as fidgeting, gardening, cleaning the house, dancing in the shower etc.

As you can see, there are several factors that account for the ‘calories out’ part of our equation and the important thing here is to understand how to calculate the sum of all these factors. Calories out are fundamental in understanding what your balance of ‘calories in’ should be. Thankfully, a very clever equation was created in 1918 (and subsequently updated to improve accuracy) which gives you all you need to be able to calculate this magic number – introducing The Mifflin-St Jeor formula! 

This equation is widely accepted as one of the most accurate ways in which to calculate your TDEE, it is based on your gender, age, sex and weight in order to give you a personalised sum of calories burned each day before activity levels are taken into consideration. In a 2005 Systematic Review by David Franklin, comparing the most commonly used BMR calculators, it was found that the Mifflin-St Jeor equation was more likely than its counterparts to estimate BMR within 10% of that measured. There are multiple online calculators available which do the heavy lifting for you, but these aren’t always accurate, often the best approach is to get your calculator out and do the maths yourself.

There are 3 steps to follow:

Step 1 - Calculate BMR (Mifflin-St Jeor Formula)

To calculate your BMR, you will use your sex, age and weight to personalise the formula.

For males, use the following equation:

• (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) + 5 = BMR for males

For females, use the following equation:

• (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) - 161 = BMR for females

For example, a 39 year old, 57 kg, 5 foot 6 inch tall woman has a BMR of 1,338.8 (equation: (10 x 57) + (6.25 x 167.64) – (5 × 39) - 161 = 1,261.75).

Step 2 - Calculate activity level

The next step is to select the correct multiplier based on your average activity levels per week:

• 1.2 - sedentary (little to no exercise)

• 1.375 - lightly active (light exercise 1-3 days per week)

• 1.55 - moderately active (moderate exercise 3-5 days per week)

• 1.725 - very active (hard exercise 6-7 days per week)

• 1.9 - extra active (very hard exercise, training, or a physical job)

For example, a Delivery Man who walks all day for their job would have an activity level of 1.725 depending on the length and difficulty of their route.

An office worker who walks several times a week for exercise would have an activity level of 1.55. On the flip side, an office worker who is very sedentary at work but carries out high-intensity training 6 times per week would use the 1.725 multiplier.

Step 3 - Multiply BMR by activity level

This is the easy bit, take your BMR and multiply by your activity level. Going back to our 39-year-old female example, this individual has a desk job but takes regular breaks from her desk, walks for 40 mins daily during her lunch break and exercises 6 times per week, her multiplier would be 1.75, very active.

BMR x 1.75 would be 1,261.75 x 1.75 which would give an estimated daily calorie expenditure (TDEE) of 2,208. 

Now we understand how to calculate how many calories we burn each day. Let’s talk about how this balances, or not, with ‘calories in’ so we can use this knowledge to reach our goals.

How many calories should I eat per day - (Calories In)

Once you understand how many calories you expend per day, you can use this information to consume the correct amount of calories per day in order to elicit the result you are seeking.

So, there are three outcomes to consider – weight gain, weight loss, weight maintenance. Let’s look at each.

Calculate calorie intake for weight gain

This is for those of you wondering ‘how many calories should I eat to gain muscle’. In order to gain weight, you will need to consume more calories than you expend. This is called a ‘calorie (or caloric) surplus’. Unless an individual is seriously underweight, they would generally want to gain weight in the form of muscle, not fat. This is also known as a ‘lean bulk’. Many of my clients have a muscle mass goal, I recommend they have a 10% calorie surplus, so they consume 10% more calories than they burn. 

Returning to my example of a 39-year-old female, her current total daily calorie expenditure is 2,208, I would calculate 10% of this figure, giving me 220 additional calories to add to her daily intake levels, she would therefore have a goal of consuming 2,428 calories per day, whilst maintaining her current activity levels. 

This would of course be regularly reviewed and if weight gain was rapid, significant, or fat rather than muscle was being gained, it would be tweaked and vice versa. It’s worth mentioning here, that although this article isn’t about lean bulks in general, I’d be remiss not to mention that the macronutrients making up this caloric surplus need to be appropriate. The diet should be high in protein, carbs and nutrient-dense – eating insufficient protein levels will not support muscle growth, so weight gain would likely be via accumulated body fat.

Calculate calorie intake for weight Loss

How many calories should I eat to lose weight?…If my 39-year-old female client was looking to lose weight by way of reducing her body fat levels, I would reduce her calorie intake by 10-40% (40% is extreme), whilst maintaining her activity levels – also known as a ‘calorie deficit’. Let’s be sensible and reduce them by 10%, this would bring the daily calorie target down to 1,988 per day and again would be reviewed regularly to ensure weight loss is at the correct rate and tweaked where needed. We would also have conversations about how they are feeling, are they too hungry, tired etc, as these are all indicators of an unsustainable deficit and although it may elicit short term weight loss, it could be that we need to up the calories slightly in order to sustain the deficit long enough to meet our goal.

We could, of course, do the reverse and add more activity into this individuals week, however, given her current activity levels, this would likely lead to overtraining. If an individual was sedentary, we would look at increasing activity in order to raise the TDEE, allowing for a more generous caloric intake. Or we can do a little of both, decreasing calories and increasing activity. An effective fat loss diet is one that is sustainable, so decreasing calories too low will leave less room for the foods we love and will be harder to maintain.

Again, I need to just mention that the foods making up the calorie intake should be high protein and nutrient-dense in order to encourage muscle growth and repair, whilst in a deficit and to also ensure you are consuming sufficient vitamins and minerals to keep your body healthy and functioning as it should.

Calculate calorie intake for maintaining weight

No maths required here folks, you balance your calories in and calories out equally. So, in order to maintain her weight, my 39-year-old female would maintain her current activity levels and consume 2,208 per day. Easy peasy.

That’s it! You now know how to calculate your calorie expenditure per day and use this knowledge to calculate how many calories you should eat per day in order to meet your goal. However, there is one more important thing for me to mention and it’s a topic that to some, is scarier than a calorie deficit on a weekend. Tracking.

Importance of Food Tracking

We now know that calories are key to weight management, so, logically, you’ll need a tool that facilities and, in many cases, simplifies the terrifying act of logging and tracking the foods you consume each day.

There are many, many effective tracking tools out there, free and paid for. They have many built-in features that allow for ease of tracking, like a meal builder that allow you to create a meal you have regularly, so several foods can be added in a single click. 

It might seem daunting, but tracking your food doesn’t have to be time-consuming and many people are pretty surprised by just how much they underestimate their food intake. Like anything, do it for a few days and it quickly becomes a habit. A good habit. You may need to weigh foods at first, but you’ll quickly be able to assess the weight by eye, which will of course save time, and don’t forget that many tools have barcode scanning capabilities so you can log food in seconds. Ultimately, if you don’t track your food, you do not know what your calorie intake is.

Here (in no particular order) are my top 2 food tracking tools:

1. MyFitnessPal - Been around for donkey’s years, mature platform, very easy to use, fast to navigate, supports activity tracking too and the basic (but very good version) is FREE!

2. Fitbit - Very similar to MyFitnessPal, but you wear a watch that relatively accurately tracks TDEE when used alongside the app for manual tracking. The app is free but you will need to buy a watch, the starting price is around £100

A parting shot…

I have mentioned the word ‘sustainable’ many times during this article. Sustainability is key if you want to meet your goals, a goal should challenge you and take your body further than it wants to go; that takes time, consistency and dedication. If you don’t support your goals with a sustainable diet, you won’t be able to see it through or you will hit your goal and revert because you’ve deprived yourself for so long and literally lost the will to live.

I have a few parting tips to share that will help you maintain your calorie target, mostly around those in a deficit, as that is, for many, the hardest target to maintain:

1. Target an 80/20 split of nutrient-dense and not so nutrient-dense foods. 80% of your diet should be nutrient-dense foods that are conducive to your goals, the other 20% should be the foods you love that may be high sugar/high-fat foods

2. You can save calories for an occasion, although try to keep it as controlled and infrequent as you can. If you now you are eating out on Friday, you can reduce your calorie intake before or after the event in order to compensate for the additional calories

3. It’s easy to decide not to track a day where you eat more than your target, it’s easy to write this off as a bad day and not track it. You should resist this and still track, as you can easily follow step 2, and save those additional calories later. Or, don’t save them and at least you’ll understand why you gained weight this week because it’s easy to forget those big meals or days

4. Don’t eat to compensate for additional activities. If you have an extra active day, don’t then eat more food, reap the benefits of that additional activity! 

5. For those of you that are on a lean bulk, it can also be tough for many that have been in a weight loss mindset for some time. Don’t rush the calorie increase, take it slow, trust the process and don’t be tempted to make up the surplus with low nutrient foods.

6. Regardless of whether you are working on gaining or losing fat, always track your progress so you can see the path you are on and change it if needed

7. Track your calories

8. Track your calories

9. Track your calories ;)

If you want help calculating the correct calorie intake for your goals along with an effective, tailored training plan and unrivaled support, check out my Online Personal Training Service.