How many calories should I eat in a day? It's a common question many registered dietitians hear. The truth is, it's not a one-size-fits-all answer. In general, the 2015-2020 Dietary Guidelines suggest that adults will likely need somewhere between 1,600 and 3,000 calories per day — a wide range. Trying to determine how many calories an individual needs a day can vary by several factors including age, gender and lifestyle. Whether or not someone wants to lose weight also plays a role in how many calories they should consume daily. Here’s a look at how calorie needs are calculated and a few examples of calorie needs for different types of people.

First, What Is a Calorie?

Technically, a calorie is a unit of energy. Put simply, when we eat calories from food they are converted to energy for breathing, circulation, brain and muscle function, and cellular work. Basically, all of your body's essential functions run on calories! In addition to fueling your body, calories can support overall health. When you eat a wide range of healthful foods, those calories contain a variety of nutrients that allow your body to function optimally. For example, calories from yogurt offer nutrients that benefit bone and gut health because yogurt contains calcium and probiotics, respectively.

How to Calculate Calorie Needs

The Harris-Benedict Equation is a standardized equation commonly used to assess calorie needs. If you have ever used an online nutrition calculator chances are it was modeled on this evidence-based method. Most calculators ask you to input demographic information including age, gender, height and weight to calculate baseline calories needs or Basal Metabolic Rate (BMR). This number can then be scaled by a physical activity factor to account for the amount of exercise that person does regularly.

To see the Harris-Benedict equation in action, here’s how the numbers compute for various individuals that weigh 150 pounds and are 5 feet, 7 inches tall. Since metabolism and metabolic rate are influenced by age, gender and the amount of exercise you do, you'll see a variation across age and gender groups.

Keep in mind, there is a genetic component to metabolism that cannot be accounted for by an equation such as this.

18-year old female, exercises 2-3 times per week

Daily calorie needs: 2365 calories

25-year old male, exercises 6-7 times per week

Daily calorie needs: 3182 calories

40-year old female, exercises 1-2 times per week

Daily calorie needs: 1967 calories

70-year old male, exercises 4-5 times per week

Daily calorie needs: 2448 calories

Bottom Line: Calories Count, But What You Eat Matters More.

Calories matter, but eating high quality food that you enjoy matters more! All calories are not created equal. Simplifying calories down to one number neglects to consider two important factors about food: nutrition density and digestion time.

Nutrient density is all about the quality of the calories. If you compare 100 calories of soda and 100 calories of milk, you have 100 calories either way but that’s not the whole story. While soda only offers up calories from sugar, milk provides 13 essential nutrients including protein, calcium, and vitamin D making it the more nutrient dense option. Ideally, you want most of your calories to be as nutrient dense as possible to maximize health.

Digestion time varies significantly by the type of foods you eat, and in what combination you eat them. Carbs are typically digested and metabolized the fastest, while protein and fat take longer; high fiber carbs (like oats and brown rice) will also slow digestion. Slower digesting calories are ideal to help curb cravings throughout the day and to prevent a mid-day energy slump. Choosing nutrient dense calories that keep you satisfied is the goal.

Dana Angelo White, MS, RD, ATC, is a registered dietitian, certified athletic trainer and owner of Dana White Nutrition, Inc., which specializes in culinary and sports nutrition. She is the author of four cookbooks First Bites: Superfoods for Babies and Toddlers, The Healthy Air Fryer Cookbook, The Healthy Instant Pot Cookbook and Healthy Quick and Easy Smoothies.

*This article was written and/or reviewed by an independent registered dietitian nutritionist.

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