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How Many Calories Should I Eat to Lose Weight?

By Ann Olson

calorie counting chart appleYou want to lose weight, so you’re planning to cut calories. But how many calories do you actually need to intake to effectively lose the pounds?

People often fall for common diet myths and make the mistake of eating too few calories for their bodies, which can lead to deprivation, metabolism slow-down, and, in some cases, unwanted binging.

To lose weight effectively, it’s important that you eat in a caloric deficit manner that is appropriate for your body type, activity level, and weight. To do this, you must determine your ideal caloric intake, using the same foolproof methods nutritionists use to assist their clients.

How to Determine Your Necessary Caloric Intake

The three most important components when determining your necessary caloric intake include:

  • Your basal metabolic rate (BMR)
  • Your activity level
  • Your base maintenance intake

Step #1: Determine Your BMR

Your BMR is the amount of calories you need daily to ensure that your vital organs, such as the heart, lungs, or nervous system, are able to function sufficiently. To figure out how many calories you need to lose weight, first you’ll figure out your basal metabolic rate, or BMR. Once you figure out your BMR, you will use that number to figure out your appropriate calorie needs.

To figure out your BMR, you can use one of these two scientific formulas:

1. Katch-McArdle Formula
To use this formula, you must first know your body fat percentage. The most accurate way to determine your body fat percentage is by getting a DEXA scan at your local hospital. You can also get an estimate at home by using the Accu-Measure calipers.

This is a two-step formula. Before you arrive at your BMR, you must first calculate your lean body mass, or LBM:

LBM = [total weight (kg) x (100 - body fat percentage)] / 100

This may be difficult to figure out, so let’s use an example. Mary, a relatively healthy adult female, wants to know her BMR. She knows her body fat percentage is 24%. Her weight is 140 pounds, or 63.6 kilograms.

First, she needs to figure out her lean body mass. Using the lean body mass formula above, the formula should look like this:

  • LBM = [63.6 kg * (100-24)] / 100

After solving this equation, she gets the answer 48.336 kg, her lean body mass.

Now input Mary’s lean body mass into the Katch-McArdle formula:

  • BMR = 370 + (21.6 * LBM).

Mary’s LBM is 48.336, so her BMR is 1,414.06.

body fat calipers

2. The Mifflin-St. Jeor Formula
The Katch-McArdle formula is a good formula if you know your body fat percentage, but what if you don’t know it? Alternatively, you can use the Mifflin-St. Jeor formula to figure out your BMR.

The Mifflin-St. Jeor formula is as follows:

  • For women: BMR = 655 + [9.6 * weight (kg)] + [1.8 * height (cm)] – [4.7 * age (years)]
  • For men: BMR = 66 + [13.7 * weight (kg)] + [5 * height (cm)] – [6.76 * age (years)]

To figure out your BMR, input your weight in kilograms and your height in centimeters. If you do not know how to convert your height or weight to kilograms or centimeters, use an online converter tool. Then, input your age and solve.

For example, let’s take Lori, a 22-year-old woman who is 68 inches tall (172.72 cm) and weighs 150 pounds (68.18 kilograms). Since she is a woman, we’ll use the female formula for this equation.

  • Input her data into the formula: BMR = 655 + (9.6 * 68.18) + (1.8 * 172.72) – (4.7 * 22)
  • Lori’s BMR is 1,517.02.

Once you calculate the BMR, figure out your activity factor.

Step #2: Determine Your Activity Factor

Unfortunately, people make the mistake of dieting below their BMR, thinking that it’s the amount of calories they need on a daily basis. This is simply incorrect – your BMR determines your calorie needs if you were in a coma, or just enough to ensure your vital organs are able to function healthily. You’re not comatose, so you’re going to use an activity factor to figure out how many calories you truly need everyday.

So what’s an activity factor? It’s a multiplier that determines how much your calorie needs increase as a result of your overall activity level. For example, Jill the bodybuilder works out five hours a day, so his calorie needs are higher than Jane the receptionist, who is stationary for most of the day. The more active you are, the more calories you need.

Here are the activity factors:

  • 1.2: Sedentary (little to no daily exercise)
  • 1.3 to 1.4: Lightly active (little daily activity, plus exercise one to three times per week)
  • 1.5 to 1.6: Moderately active (moderate daily activity, plus exercise three to five times per week)
  • 1.7 to 1.8: Highly active (active daily lifestyle, plus hard exercise six to seven times per week)
  • 1.9 to 2.0: Extremely active (hard, active daily lifestyle combined with daily exercise or sports)

For example, let’s take Joanne, whose BMR is 2,000 calories. She works a slow desk job all day and does not exercise. This qualifies her as sedentary, so let’s multiply 2,000 calories by 1.2, which equals 2,400 calories. Simply multiply your BMR by the activity factor that closely matches your lifestyle, and the end result is your maintenance intake, the number you need to maintain your current weight.

exercise bikes group

Step #3: Determine Your “Weight Loss Calories”

Once you determine your true maintenance level, you’re going to use that number to figure out your caloric deficit. This will ensure you’re losing weight safely and steadily.

To lose weight in a steady manner, use the 10% to 20% rule: Subtract 10% to 20% of your total caloric intake to lose weight. For instance, let’s take Joanne in the previous example, whose maintenance intake was estimated to be 2,400 calories. 10% subtracted from 2,400 is 2,160. Subtract 20% and you’ll get the number 1,920. Therefore, a safe caloric deficit for her is between 1,920 to 2,160 calories.

Using the 10% to 20% rule, most people lose between one to two pounds per week – some of that being fat and some of it being water and muscle weight, depending on your activity and protein consumption.

Final Word

At the most, aim for a one- to two-pound loss per week, which ensures you’re losing weight at a safe, maintainable weight. Instead of using any arbitrary number as a rule to lose weight, such as 1,100 or 1,300 calories, figure out your true necessary caloric intake by factoring in your BMR and activity level to be certain you’re not endangering your health and undercutting your weight loss efforts by eating too little.

Make sure to also focus on eating healthy, consuming mostly unprocessed, nutritious foods, such as fruits and vegetables, whole grains, lean protein, and wholesome fats. This ensures you stay healthy while losing weight.

How do you typically determine the number of calories to eat in order to lose weight?

(photo credit: Shutterstock)

Ann Olson
Ann Olson is a health writer and full-time frugalista currently living in Minneapolis, Minnesota. Saving money is her passion, and she'll cut any corner in the pursuit of becoming passively wealthy. She's also a diet expert and amateur bodybuilder who credits her active lifestyle for keeping her healthy and happy.

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  • Kristin

    For Lori’s calculation, you didn’t convert her height to cm and left it in inches. I calculate her BMR would be 1517 calories.

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