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How Many Calories Do You Need?


How Many Calories Do You Need In A Day?

When it comes to your fitness and overall health goals it comes down to one thing – calorie intake. What’s a calorie? In a lab, it’s the amount of energy required when something is heated to make 1 gram of water rise 1 degree. For simplicity sake, (and because our bodies aren’t really a lab) it’s the amount of potential energy that food has. For example, that slice of pizza you’re holding on to has the potential of 500 calories. With that, your body will either use it (a.k.a burn calories) or store it for future use in the form of fat.

How Your Body Uses Calories

Let’s face it, a lot of us look at calories as something to burn off – especially if we’re exercising or “trying to cut down on calories.” Our bodies however, still need a certain amount of calories just to function. If you were to do nothing all day long, your body would still use calories. This comes down to something called a Basal Metabolic Rate or BMR. It’s the amount of calories required just to survive.

Think of a BMR like this:

If you were sitting on a couch, not doing anything your body is still functioning. Your lungs are breathing, your intestines are churning, your muscles are using up energy, and your kidneys are filtering your blood. All of the metabolic processes that are going on inside your body are using up energy. A basal metabolic rate is the minimal amount of energy the body uses to support itself in a fasting state when resting and awake in a warm, quiet environment. Some people use a BMR calculation to find out how many calories they are burning at rest. However, the BMR is not an accurate indicator of how many calories you burn at rest. The BMR is a resting/fasting state of close to twenty-four hours. This includes not eating. Many people simply don’t achieve this state in a given twenty-four hour period.

To figure out how many calories we need in a day we will not be using the BMR calculation If you’re still curious, here’s the calculation to find out the calories burned at a complete resting phase:

For men: 1kcal/kg/hour
For women: 0.9kcal/kg/hour
Converting pounds to kg: 2.2kg for every pound

A lot of website on the internet of even personal trainers at the gym use this calculation for daily calories but it’s not the most accurate number of your calorie needs.

The Resting Metabolic Rate:

The term BMR only applies to a person at rest. Which means, if you’re not fasting or if you’re not completely rested, then your energy needs are roughly 6% higher than the BMR (1). For example, you wake up in the morning, have some coffee, maybe a snack, then proceed to watch football on the couch all day – that is truly not a resting state so your caloric needs will be higher. Typically, unless you’ve been sleeping for a good 8-10 hours and have been fasting for at least 12 hours, then the RMR is the more accurate number for how many calories our bodies use. Some websites and gyms use the RMR calculation but it’s still not the best calorie calculation. Add 6% to the BMR number to find out how many calories you really burn.

Accurately Calculating Your Caloric Needs

The Institute of Medicine came up with a more accurate formula to determine our calorie needs that is more accurate than that of the RMR or BMR calculation. The formula looks like this and it’s called the Estimated Energy Requirement:

Men (19 and older): EER= 662 – (9.53 x age) + PA x (15.91 x WT + 539.6 x HT)
Women (19 and older): EER= 354 – (6.91 x age) + PA x (9.36 x WT + 726 x HT)

EER: Estimated Energy Requirement
Age: In Years
PA: General physical activity level (see below)
WT: Weight in kg (pounds/0.45)
HT Height in meters (inches/39.4)

Physical Activity Estimates:
Sedentary (no exercise): Men: 1 Women: 1
Low activity (walks of 2 miles/day): Men: 1.1 Women: 1.12
Active (walks equal to 7 miles/day): Men: 1.25 Women: 1.27
Very Active (walk equal to 17 miles/day: Men: 1.48 Women: 1.45

There you go, simple right? There you have (your general) calorie needs for the day. The physical activity estimates are based off of your general life. For example, if you work a desk job for 10 hours a day, you might want to put sedentary. Of course, if you go to the gym and are very active for the remainder of the day, you can factor that into your calorie needs as well. Luckily, you don’t need to do the calculation yourself, we’ve got the calculator below to plug in all your info for your calorie needs.

The Best Way To Find Out How Many Calories You Burn

The Estimated Energy Requirements equation can give a person a general idea on how many calories someone needs in a day. However, it will never be 100% accurate. There are so many individual factors and personal factors (like the ones talked about earlier) that affect how many calories a person burns throughout the day.

Estimated Energy Requirement Calculator


There you have it – your estimated caloric intake. Keep in mind this is an average number and not 100 percent accurate for anyone. Like I mentioned, there are so many other factors that go into a metabolism can either cause this number to be higher to lower (see below to see the best way to figure out how to figure out your calorie needs for the day).

Factors That Affect How Many Calories You Burn

1. Greater lean body mass: muscle requires more energy to maintain
2. Larger body surface area: bigger space uses more energy to maintain
3. Males: generally, males use up more energy than females due to larger body surface area, increased body mass, and hormones (generally speaking)
4. Temperature: Increased temperature requires more energy as does the cold
5. Thyroid Hormones: hypothyroidism expends less energy
6. Your nervous system: is your flight or fight response turned on? Higher levels of stress use up more energy
7. Pregnancy: you’ve got something inside you…
8. Stimulants: caffeine, cocaine, etc.
9. Illness: increases stress and energy demand of your body
10. Age: The rate at which your body burns calories generally decreases about 1-2% each decade after 30.
11. Eating food: Eating food causes more calories to be burned too. In some cases up to 10% It’s known as the thermal effect of food.

Thermal Effect Of Food (TEF)

The thermal effect of food is known as the increase in metabolism that occurs during digestion and absorption of food. Here’s the kicker. If you eat mostly carbohydrates, your TEF if 5-10% vs 20-30% for protein consumed. Fat on the other hand is about 0-3%. The total TEF is 5-10%. So if you ate 3000 calories it would take about 150-300 calories to burn.

The Best Way To Calculate How Many Calories You Burn:

1. Begin with the EER equation as a baseline
2. Use a food diary site to see how many calories you are eating and how close you are getting to your actual goals.
3. Factor in exercise/your general activity level – if you exercise, you’re burning more calories. You’re going to have to add that on to your EER equation.
4. Weigh yourself once a week
5. Write down your goals – are they to gain weight, lose weight, or maintain weight?

By keeping track of your calories and using the EER equation as a baseline you’ll be able to see your results. If your goal is to lose weight but you’re not, you might need to lower the amount of calories you take in. If your goal is to gain weight but you’re losing it, you might need to add more calories to the EER equation.

Also remember, weight is just a number. You may be gaining weight or staying the same – especially if working out is new to you or you’re doing more than usual. You might be adding muscle weight but losing fat in the process. This is why there is more monitoring than just the scale. If you feel good and are happy with the way that you look, then keep doing what you’re doing.

What are some of the ways you’ve found to accurately track your fitness goals?

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1. Hampl, Jeffry S. Wardlaw, Gordon, M. Perspectives in Nutrition. 7th ed. New York: McGraw-Hill Companies Inc., 2007. 468-473.
4. Porth, Carol Mattson, RN, MSN, PhD. Matfin, Glenn, MB ChB, DGM, FFPM, FACE, FACP, FRCP. Pathiophysiology: Concepts of Altered Health States. Philadelphia: Wolters Kluwer Health | Lippincott Williams & Wilkins. 983-984. Print.

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  • Airi

    Thanks for this interesting article about calorie intake

  • Shauna

    Thanks for this. A few people ask this occasionally on myfitnesspal, I will refer them here. FYI, there’s an error with the calculator. A pop-up pops up over the following field if you put a decimal in your height or activity level, which you need to do!

  • Thanks! I’ll try to fix it as soon as possible.

  • Thanks, glad you could find it useful!


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