One of the most important things to do when embarking on a training programme or new nutrition plan is to calculate your caloric requirements. This means working out how many calories you need for any given health and fitness goal and is the only way you will be able to change your body composition.
The main number you will need to find when working out your caloric requirements is your basal metabolic rate (BMR calculator). The human body burns through calories even at rest. Basic human functions like breathing, repairing muscle tissue, cell regeneration and renewal, alongside the processing of nutrients and oxygen, all use a lot of energy: your BMR is the number of calories that your body needs in order to fulfill all of these functions.
Once you know your BMR, any changes you want to bring about in your body become suddenly much more achievable.
You can find out more about BMR on our BMR Calculator
BMR and calorie calculators
Weight loss requires a caloric deficit and weight gain requires a caloric surplus. Knowing exactly how much food to eat to achieve any deficit, surplus, or even maintenance, requires knowing how much energy your body uses which, as we have just seen, is your BMR.
It’s easy enough to find a pretty decent estimate of your BMR. Though actual amounts will vary according to person, with far too many variables to take into account for any calculator to be 100% accurate all the time, a simple calorie calculator will be able to put you in the right ballpark.
Calorie Calculators will be based on one of several equations, all of which will give you an estimated average daily caloric expenditure. The Harris-Benedict Equation is one of the main ones used to calculate basal metabolic rate (BMR) and was one of earliest equations written for this purpose. It was revised in 1984 to be more accurate and was used up until 1990, when the Mifflin-St Jeor Equation was introduced. The Mifflin-St Jeor Equation also calculates BMR and has prove more accurate a lot of the time than the revised Harris-Benedict Equation.
The Mifflin-St Jeor and Harris-Benedict equations remain the two most commonly used BMR equations with most calorie calculators. They are:
Mifflin-St Jeor Equation
For men: BMR = 10W + 6.25H - 5A + 5
For women: BMR = 10W + 6.25H - 5A - 161
Revised Harris-Benedict Equation
For men: BMR = 13.397W + 4.799H - 5.677A + 88.362
For women: BMR = 9.247W + 3.098H - 4.330A + 447.593
W= weight in kilograms, H= height in centimetres, A= age in years
The value obtained from these equations is the estimated appropriate calorie intake a person should hit in a day to maintain their bodyweight if they are doing no physical activity. This value is multiplied by an activity factor (generally 1.2-1.95), dependent on a person's typical levels of activity, which will give a more realistic value for maintaining bodyweight.
To include the number of calories you burn during daily activities based on your lifestyle and activity levels, a calorie calculator will make use of some variation on the following multiplications:
- Sedentary:If you get little or no exercise, multiply your BMR by 1.2.
- Lightly active.If you lightly exercise one to three days per week, multiply your BMR by 1.375.
- Moderately active.If you moderately exercise three to five days per week, multiply your BMR by 1.55.
- Very active.If you take part in hard exercise six to seven days per week, multiply your BMR by 1.725.
- Extra active.If you engage in very hard exercise six to seven days per week or have a physical job, multiply your BMR by 1.9.
The number you will get from this is the number of daily calories you need in order to maintain your current weight, at your height, weight and age, with your physical activity levels. These are rough guides: you may need to play around with the numbers to better suit your needs as you go along.
You can use this calculator to work out how to use caloric intake to meet your health and fitness goals. Generally speaking, it will take an average daily caloric deficit of 500 calories to lose 1lb (0.5kg) per week. Inversely, it will take an average daily surplus deficit of 500 calories to gain 1lb (0.5kg) per week.
Therefore, if your BMR is 2,500, you will need to eat around 2,000 calories per day to lose 1lb/0.5kg per week. You would need to eat around 1,500 calories per day to lose 2lbs/1kg (any more than this is not recommended and should only be attempted under medical supervision).
Alternatively, if you were looking to gain weight, you would want to eat around 3,000 calories per day to gain 1lb/0.5kg per week, or 3,500 to gain 2lbs/1kg.
In this way, we can use BMR calculator, calorie calculators and calorie tracking to make sure we are always eating what we need to be to get the results we want.