Weight Loss 101: How to Calculate a Calorie Deficit

23 05 2011

By Matt Fitzgerald
For Active.com

To lose weight, you have to eat fewer calories than your body burns each day. It seems simple enough. What’s not so easy is actually doing it. How do you know if you’re actually eating fewer calories than your body burns? Exactly what size of “calorie deficit” should you aim for? And how can you make sure you’re hitting the mark?

These are the questions you must answer to get on track toward your weight-loss goals. So let’s answer them.
The Calorie Deficit Sweet Spot

The easiest way to ensure you eat fewer calories than you burn is, of course, to eat very little. If you have an apple for breakfast, a small salad for lunch, a piece of toast for dinner and nothing else, you can be pretty sure you’re maintaining a calorie deficit. But you’ll also be miserable with hunger and a lack of energy.

The optimal calorie deficit is large enough to stimulate steady fat loss, but not so large that you’re always hungry and lethargic. Avoiding a calorie deficit that is too large is even more important for athletes, who need to keep their muscles well-fueled for training. The calorie deficit “sweet spot” for athletes is 300 to 500 calories per day.
Do the Math

Your ultimate goal is to figure out exactly how many calories to eat daily to lose weight without being hungry and lethargic and without sabotaging your training. To do that you need to figure out how many calories you burn each day and then subtract your target deficit of 300 to 500 calories from that number.

There are two components to your total calories burned daily: calories burned at rest and calories burned in workouts.

To begin, add up the total number of hours you train in a typical week and divide that number by seven to yield the average number of hours you train daily. For example, suppose you train seven hours per week on average. This works out to one hour per day. Next, multiply this number by your body weight in pounds and the average number of calories you burn per pound of body weight per hour of training. The average number of calories you burn per hour of training is influenced by your speed. Use this table to get the appropriate multiplier.

Training Speed

Calories per pound per hour

Slower (run 11:00/mile) 4
Average (9:30/mile) 5
Faster (7:00/mile) 6

The result of this calculation is the average number of calories you burn through exercise daily. For example, suppose you run one hour per day on average, you weigh 150 pounds, and your speed is slower. In this case, 1 hour x 150 pounds x 4 calories per hour = 600 calories per day on average through exercise.

Your next step is to calculate your calories burned at rest (i.e. outside of workouts) during the day. To do this, first visit the caloric needs calculator and enter the information requested. In the “Activity Level” field enter “Sedentary” if you are mostly inactive outside of your workouts (that’s most of us) or “Lightly Active” if you have a physical job. Do not select “Active”, as this option is intended to account for your workouts, which you’ve already accounted for separately for greater accuracy.

The result is an estimate of the number of calories you burn in 24 hours outside of exercise. But since you spend part of those 24 hours working out, we need to remove that part from the estimate.

To do this, take your estimate of calories burned at rest and divide it by 24, then multiply the result by the number of hours per day that you do not spend working out. For example, suppose your calculated calorie usage outside of exercise is 2,000 calories per day. If you work out 1 hour per day on average, then there are 23 hours of the day when you’re not working out. In this case, your daily calories burned at rest is (2,000 calories per day ÷ 24 hours per day x 23 hours a day you do not work out = 1,916 daily calories burned.

To determine the total number of calories you burn daily, add together your average daily exercise calories burned and your calories burned at rest. So, if you burn 1,916 calories per day at rest and 600 calories per day through exercise, then the total number of calories your body burns per day on average is 2,516.

This number also represents the total number of calories you would need to consume daily to maintain your current weight.

The total number of calories you should aim to consume is equal to the number of calories you would need to eat daily to maintain your current weight minus your chosen calorie deficit. Remember, the appropriate deficit range is 300 to 500 calories. Let’s say you choose 400. Then you should aim to eat 2,116 calories per day (2,516 total calories burned per day – 400 calorie deficit) during your weight-loss initiative.

For more guidance on establishing appropriate daily calorie targets and complete weight-loss programs for endurance athletes, including comprehensive meal plan and training plans, check out my Racing Weight Quick Start Guide.

Active Expert Matt Fitzgerald is the author of several books on triathlon and running, including RUN: The Mind-Body Method of Running by Feel (VeloPress, 2010), Runner’s World Performance Nutrition for Runners (Rodale, 2005) and Brain Training for Runners.

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23 05 2011

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