We are all likely aware that the general guidance for calorie intake in the UK is 2000 kcal per day for women and 2500 kcal per day for men. When it comes to finding out a more precise answer to “how many calories should I eat a day”, there are a few more variables to take into consideration.
The general guidelines are a great reference, but some people may need more calories and some may need less.
If you are looking to control your weight, calculating your calorie intake is easily one of the most beneficial things you can do.
Why do I need to work out how many calories I should eat a day?
Changing your weight predominately comes down to the numbers. In order to lose weight, you are going to need to create a calorie deficit. You will need to create a surplus in order to gain weight. You will need to balance your calories to maintain your weight.
It is easy to see why it is so important to work out how many calories you should eat a day.
So, how do I work out how many calories I should eat a day?
The amount of calories each person needs to eat in a day is very specific to their weight, height, age, activity levels, physical build and metabolism. Unfortunately, it is quite difficult to get an exact number, but we can get very close.
Introducing BMR and TDEE
BMR stands for basal metabolic rate and TDEE stands for total daily energy expenditure.
BMR is the number of calories you need in order for your body to carry out basic functions and minimal movement. Your heart beating, breathing, digesting food and thinking all require energy.
Your TDEE includes the energy you need for activities above and beyond your BMR. Activities such as walking around, playing sports, visiting places all require additional energy.
The maths involved in calculating your BMR and TDEE is relatively complex. Those of you who are interested, this is coming up. If you want a quick answer to the question “how many calories I should eat a day” check out the handy calculator at the top right of this post.
The Maths
The BMR formula below is the Harris-Benedict equation which was updated by Miffin and St Jeor in 1990. It is important to note that the formula is not an exact equation, but will offer a close estimation.
Men
BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
Women
BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
Once you have worked out your BMR, you then need to add an adjustment to include energy use through activities:
Multiply your answer by the following to calculate your total energy expenditure estimation:
Sedentary (little to no exercise) BMR x 1.2.
Light exercise (1–3 days per week) BMR x 1.375.
Moderate exercise (3–5 days per week) BMR x 1.55.
Heavy exercise (6–7 days per week) BMR x 1.725
Very heavy exercise (more than once a day/heavy workouts) BMR x 1.9
How many calories do I need to eat if I want to lose/gain weight?
Once you know how many calories you need to maintain you weight, all you need to do is create a deficit. A good aim is to lose 1lb per week, which is generally 3,500 kcal per week (or 500kcal per day). You can increase this number, but don’t reduce your calorie intake by too much or your body will start preserving energy and slowing down your metabolism.
If you want to gain weight, then look to add 500kcal per day to gain 1lb per week.
If you do not have much weight to lose, you might need to make your deficit smaller, i.e., 200-300kcal per day. If you make too much of a % drop in your overall calories, you can find that your weight loss will stall.
Remember to Review
As your weight changes, and you reach your goal, you will need to repeat your calculation to work out your maintenance calories. These will be greater than your deficit calories or less than your surplus.
You may also need to tweak your calories a little to find your magic number. Unfortunately, the calculation cannot take things like individual metabolism rates or body fat ratios into account, so you may find you need to play with your intake calculation a little to find the number that is right for you.