How Many Calories Do You Need a Day? A Simple Guide

"How many calories should I eat?" is a question with an answer that is different for each person. A tall, active man needs far more than a small, sedentary woman. Two people of the same size can differ too. This guide shows how the estimate is built, with worked examples you can repeat, and the limits you should know before you act on it.

What a calorie is

A calorie is a unit of energy. The calories in food are the energy it gives you, and your body uses calories to power everything: breathing, thinking, keeping warm and moving. If you eat about as many calories as you use, your weight stays steady. If you eat more, your body stores the difference. If you eat less, it uses stores. The FDA's explanation of the Nutrition Facts label says the calorie count on a package tells you how much energy you get from one serving.

Step 1: your resting calories (BMR)

Your basal metabolic rate (BMR) is the energy your body needs at complete rest. A well-known equation for healthy adults is the Mifflin-St Jeor equation, published in 1990 by Mifflin and colleagues:

• Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5
• Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161

To change units: divide pounds by 2.205 to get kilograms, and multiply inches by 2.54 to get centimeters.

Example, man: 30 years old, 175 lb (79.4 kg), 5 ft 10 in (177.8 cm). BMR = 794 + 1,111 − 150 + 5 = about 1,760 calories.

Example, woman: 30 years old, 140 lb (63.5 kg), 5 ft 5 in (165.1 cm). BMR = 635 + 1,032 − 150 − 161 = about 1,356 calories.

Step 2: multiply for your activity

Next, multiply your BMR by a factor that matches your usual week. These factors are standard in nutrition tools. They are a judgment call, so choose the lower one if you are between two.

The result is your estimated daily energy need to keep the same weight. The man in the example needs about 2,730 calories at a moderate level, and the woman needs about 2,100. Note how both are different from 2,000. The FDA says exactly that: 2,000 calories a day is a general guide, and your calorie needs may be higher or lower.

Step 3: adjust for your goal

• To lose weight: eat below your needs. A common rule of thumb is that a gap of about 500 calories a day leads to about 1 pound lost a week. In the example, that is about 2,230 calories for the man and about 1,600 for the woman.
• To gain weight: eat above your needs, for example 250 to 500 calories more a day.
• To stay the same: eat about the number from step 2.

The 500-calorie rule is a rough guide. As you lose weight, your needs fall, and the pace slows. The CDC says that people who lose weight at a gradual, steady pace of about 1 to 2 pounds a week are more likely to keep the weight off than people who lose weight quicker. Very low calorie targets are not a good idea without medical advice.

What about protein, carbs and fat?

Calories come from three main nutrients, and each gives a known amount of energy per gram: carbohydrate 4, protein 4 and fat 9. If a plan is 40% carbohydrate, 30% protein and 30% fat of 2,000 calories, that is 800 calories from carbohydrate (200 g), 600 from protein (150 g) and 600 from fat (about 67 g). The right split depends on your goals, your health and what you can keep up.

The calorie and macro calculator does these three steps for you and turns the result into grams of carbs, protein and fat.

How accurate is it?

These formulas are estimates built from groups of people, not measurements of you. Individuals can differ by 10% or more. A few things that can move your real needs:

• Muscle mass. More muscle uses more energy at rest.
• Age. Needs generally fall with age, which the formula includes.
• Medical conditions and medicines. Thyroid problems and some medicines change your needs.
• Pregnancy and breastfeeding. The equation is not for these cases.
• Sleep and stress. They can change appetite and activity.

The best check is your own weight. Eat at your estimate for two to three weeks and weigh yourself at the same time of day. If your weight stays steady, the estimate fits. If it rises or falls, adjust by 100 to 200 calories and check again.

Calories are not the whole story

A calorie target does not tell you what to eat. Two diets with the same calories can be very different in nutrients, fiber and how full you feel. Physical activity matters too: the CDC says adults need 150 minutes of moderate-intensity physical activity a week and at least 2 days of muscle-strengthening activity each week. If you have a medical condition or you want to make a big change, talk to a doctor or a registered dietitian first.

Frequently asked questions

How many calories should a woman eat a day?

It depends on size, age and activity. The 30-year-old woman in the example needs about 1,630 calories if she is sedentary and about 2,100 if she is moderately active, to keep the same weight.

How many calories should a man eat a day?

The 30-year-old man in the example needs about 2,110 calories if he is sedentary and about 2,730 if he is moderately active. A taller or more active man needs more.

Is 1,200 calories a day safe?

It is below the needs of most adults and is often too low without medical supervision. Many calculators, including the one on this site, do not go below 1,200 for women or 1,500 for men. Ask your doctor before eating this low.

How many calories do I need to lose a pound a week?

About 500 below your daily needs is the common rule of thumb. Your own results will vary, and the pace usually slows as you lose weight.

Does eating less slow my metabolism?

Your needs do fall as you weigh less, and a very large deficit can make you lose muscle as well as fat. A moderate gap, enough protein and strength training help protect muscle.

The bottom line

Estimate your resting calories, multiply for your activity and adjust for your goal. Then test the estimate against your own weight and make small changes. The number is a starting point, and the best plan is one you can keep up.

Sources

• Calories on the Nutrition Facts label, U.S. Food and Drug Administration
• Steps for losing weight, Centers for Disease Control and Prevention
• Adult activity: an overview, Centers for Disease Control and Prevention
• Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 1990;51:241-247, PubMed
• Body Weight Planner, National Institute of Diabetes and Digestive and Kidney Diseases

This guide is general information for healthy adults, not medical advice. The examples are calculated by script with the Mifflin-St Jeor equation and standard activity factors. Last reviewed October 12, 2026.