How Many Calories Should I Eat a Day?

I guess it really depends on why you need to know the answer to that question.

For example if you want to know how many calories to eat per day so you can lose weight then the following will give you a detailed breakdown. (For both Men and Women.)

NOTE: Also check out our Calorie Calculator to Lose Weight which will give you an answer in seconds :o)

Firstly we need to calculate the Basal Metabolic Rate (BMR). This is a calculation of how many calories you would burn if you were totally at rest, without doing any kind of exercise.

 

BMR is different for both Men and Women. The following shows you how to calculate BMR:

BMR for Men (Metric)

66+(13.75*body weight)+(5*Height)-(6.8*Age)= BMR

Example BMR calculation for a man who weighs 170lbs (77kg), is 5'7" (170cm) and is 35 years old:

66 + (13.75*77) + (5*170) - (6.8*35) =
66 + (1058.75) + (850) - (238) = 1,737 Calories (BMR)

BMR for Women (Metric)

The variables used to calculate the RMR for women is different and is as follows:

655+(9.6*Weight)+(1.8*Height)-(4.7*Age)= BMR

Example BMR calculation for a woman who weighs 150lbs (68kg), is 5'5" (165cm) and is 35 years old:

655 + (9.6*68) + (1.8*165) - (4.7*35) =
655 + (652.8) + (297) - (164.5) = 1,440 Calories (BMR)

 

Once we've worked out the BMR we must add a further 'correction' to the calculation by including a facor based on the amount of physical activity done each day. By adding this correction factor you will get a more accurate picture of the amount of Calories required to maintain your weight, whilst doing this physical activity.

Here are the activity factors and the corresponding correction factor:

1.2 = very light physical activity (sitting, driving, standing,lab work)

1.375 = light exercise/sports (1-3 days/week)

1.55 = moderate physical activity/sports (3-5 days/week)

1.725 = heavy physical activity/sports (6-7 days a week)

1.9 = exceptionally heavy physical activities/sports (6-7 days a week)

 

Let's use the example above for Men and Women who do 'moderate physical activity' each day i.e. a correction factor of 1.55

BMR for Men example: 1,737 Calories x 1.55 = 2,692 Calories

BMR for Women example: 1,440 x 1.55 = 2,232 Calories

 

Ok, we're nearly there now. We now have a final calorie count which will allow us to calculate how many calories you need to have each day to lose 1lb of fat per week i.e. we need to work out a Calorie 'deficit' that will enable us to lose 'x' lbs of fat each week.

At this point we could just use divide 3,500 Calories (1lb of fat) by 7 to give us 500 calories we need to lose from the daily calorie intake.

Example man :
2,692 - 500 = 2,192 Calories (Daily calories to lose 1lb/week for a 35 year old man, who weights 170lbs,is 5'7" and does moderate physical activity every day.)

Example woman :
2,232 - 500 = 1,732 Calories (Daily calories to lose 1lb/week for a 35 year old woman, who weights 150lbs, is 5'5" and does moderate physical activity every day.)

However, rather than using a rigid 500 calorie reduction for every case it makes more sense to use a % of the amount of daily calories in case the 500 calorie calculation takes the calorie intake too low.

So a better calculation is to subtract 20% from the 'maintenance' figure to get a final daily calorie intake to lose 1lb fat per week.

Here are the final calculations:

Example Man: 2,692 - 20% = 2,154 Calories/day (Daily calories to lose 1lb/week for a 35 year old man, who weights 170lbs, is 5'7" and does moderate physical activity every day.)

Example woman: 2,232 - 20% = 1,786 Calories/day (Daily calories to lose 1lb/week for a 35 year old woman, who weights 150lbs, is 5'5" and does moderate physical activity every day.)