We all need a basic amount of energy for our bodies to function, commonly called basal metabolic rate. Your body requires this amount of energy each day even if you’re resting comfortably in a bed the whole day, awake but not moving other than breathing. These functions provide energy to cells and tissues, circulate blood, assist with breathing, and support all your organs, like the lungs, brain, digestive tract, and kidneys.
Other factors, on top of the basal metabolic rate, can influence your calorie needs. According to the Dietary Guidelines for Americans, daily calorie needs vary based on many factors, including age, sex, height, weight, physical activity level, and pregnancy or lactation status.
To maintain your weight, you need to consume about the amount of daily calories that your body requires to support your basal metabolic needs and all your regular physical activity. To lose weight, you need to eat fewer calories than your body requires at your current activity level.
A common assumption is that a deficit of 3,500 calories will lead to the loss of one pound of body weight. Research suggests that this rule of thumb overpredicts weight loss.
To calculate your estimated daily energy needs, consider the following factors.
To determine the number of calories you need to maintain or lose weight, start by weighing yourself to find your current weight. If your weight is already in a healthy range for your height, you should aim to eat the number of calories required to maintain your weight. Healthy weight can be a subjective term, but the American Cancer Society provides a chart on healthy weights and the Centers for Disease Control and Prevention (CDC) provides guidance on calculating your body mass index (BMI).
If you’d like to lose weight, use a weight loss calculator to generate estimated calorie needs for gradual weight loss at your current weight.
Choose a realistic goal weight (more on this later), or try a few different goal weights to see what the calculator will suggest for your calorie needs. Most weight loss calculators will use your goal weight to generate a calorie amount that should lead to gradual weight loss.
Date to Achieve Desired Weight
Weight loss calculators often ask your desired goal date for your desired weight to help determine your calorie goal. If you wish to lose weight faster, the calculators give a lower daily calorie goal. If you have more time for weight loss, the daily calorie goal may be higher.
Note that all weight loss calculators have limitations, and they may give you an unsustainably low calorie goal if you enter a large amount of weight to lose with a short goal date. Although this number varies depending on body size and activity level, as an RD I recommend no fewer than 1,200–1,300 calories per day for women and 1,400–1,500 calories per day for men to cover basic metabolic needs.
Biological sex affects calorie needs because of varying muscle mass and body size. Biological men tend to have larger body frames than women, with more muscle mass. Larger body sizes and more muscle mass increase calorie needs.
Calorie needs are generally higher when we’re younger and decrease over time as we age. This decrease in calorie needs results from reduced physical activity, loss of muscle mass, gains in fat mass, and lower basic metabolic needs as we age. A woman who is 35 and active has higher calorie needs than a woman who is 65 with the same activity level.
A taller person generally has more body mass than a shorter person. Bodies with more mass need more energy to carry out essential life functions, and they use more energy during physical activity, too.
Your level of physical activity affects your daily calorie needs. Consider whether you fit into one of these general activity levels listed in the Dietary Guidelines:
- Sedentary includes only the physical activity required for independent living, like showering, eating, and moving from room to room.
- Moderately active means a person walks 1.5–3 miles per day in addition to the activities of daily living.
- Active means walking more than 3 miles per day in addition to the activities of daily living.
Highly active people tend to have multiple vigorous exercise sessions (running, mountain climbing, intense interval training) most days of the week or a very physically demanding job (military or careers that require a lot of physical labor).