How Many Calories Do I Need?

Can you trust online calorie calculators?

Monica Reinagel, MS, LD/N, CNS
4-minute read
Episode #167

Lee writes: “There are lots of calculators out there that are supposed to tell you how many calories you should be eating. But they all give me different values.  How do I know what my daily calorie intake should really be?”>

If you’ve never come across one of the calculators yourself, here’s how they work: You enter in your height, weight, age, gender, and activity level and the calculator tells you how many calories you burn each day.  From that, you can extrapolate how many calories you should be eating. For example, if you are happy with your current weight, then you would eat the same number of calories that you burn each day.  If you want to lose weight, you’d want to eat less than that “maintenance” number. And, obviously, if your goal is to gain weight, you’d eat more.

It all sounds simple enough.  But if different calculators give you different results, even when you plug in the same information, how do you know which one you can trust? These calculators use various formulas to estimate the calorie expenditure for a typical person of your age, height, weight, gender, and activity level.  Different calculators yield different answers because they may use different formulas. So, which one can you trust to give you an accurate number?

Answer: None of them!

How is Calorie Expenditure Measured?

Several times a week, I get emails from readers who want me to tell them exactly how many calories they can eat in order to maintain their weight or lose a certain amount of weight.  Unfortunately, the only way to find out would be to go to a research laboratory and spend 24-hours in a special chamber, or wear a mask or hood that measures your actual energy expenditure as you go through your daily activities.

For most of us, this is obviously not practical. And even though this might give you a much more accurate answer than a formula, it is still only a snapshot of a single day.  Your metabolism is affected by many things, including diet, age, body composition, even how hot or cold the environment is.   I’ve talked about many of these factors in previous articles. For example:


About the Author

Monica Reinagel, MS, LD/N, CNS

Monica Reinagel is a board-certified licensed nutritionist, author, and the creator of one of iTunes' most highly ranked health and fitness podcasts. Her advice is regularly featured on the TODAY show, Dr. Oz, NPR, and in the nation's leading newspapers, magazines, and websites. Do you have a nutrition question? Call the Nutrition Diva listener line at 443-961-6206. Your question could be featured on the show.