How Many Calories Should I Eat per Day? A Step-by-Step Guide

What determines how many calories you burn

Your total daily energy expenditure (TDEE) is the number of calories your body uses in a day. If you eat about that many calories on average, your weight stays roughly stable, which is why TDEE is often called your maintenance calories.

TDEE has three main parts. Basal metabolic rate (BMR) is the energy needed to keep you alive at rest: breathing, circulation, brain function and maintaining body temperature. For most people it is the largest share of daily burn. The thermic effect of food is the energy used to digest and process what you eat, roughly 10% of intake, and it is higher for protein than for carbohydrates or fat. Activity covers both planned exercise and everything else you do, such as walking, standing, cleaning and fidgeting.

Non-exercise activity varies a lot from person to person. Two people of the same size can have very different needs simply because one has a desk job and the other is on their feet all day. This is one reason any formula gives an estimate, not a precise answer.

Step 1: Estimate your BMR with the Mifflin-St Jeor equation

The Mifflin-St Jeor equation is one of the most widely used formulas for estimating resting energy needs in adults, and it is generally considered more accurate for most people than older equations such as the original Harris-Benedict. It uses weight in kilograms, height in centimeters and age in years.

For men: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) + 5. For women: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) - 161. To convert, divide pounds by 2.2046 to get kilograms and multiply inches by 2.54 to get centimeters.

Worked example: a 35-year-old woman who is 165 cm (about 5 feet 5 inches) tall and weighs 70 kg (about 154 pounds). Weight: 10 x 70 = 700. Height: 6.25 x 165 = 1,031. Age: 5 x 35 = 175. So BMR = 700 + 1,031 - 175 - 161 = about 1,395 calories per day. That is roughly what her body would burn if she stayed in bed all day.

Step 2: Multiply by an activity factor

To turn BMR into TDEE, multiply it by an activity factor. The commonly used multipliers are: 1.2 for sedentary (little or no exercise, desk job), 1.375 for lightly active (light exercise 1–3 days a week), 1.55 for moderately active (moderate exercise 3–5 days a week), 1.725 for very active (hard exercise 6–7 days a week) and 1.9 for extremely active (physical job plus hard training).

Continuing the example, if the woman walks regularly and does light workouts twice a week, she would use 1.375: 1,395 x 1.375 = about 1,920 calories per day. That is her estimated maintenance intake.

A second example: a 40-year-old man who is 180 cm (about 5 feet 11 inches) tall, weighs 85 kg (about 187 pounds) and trains four days a week. BMR = 850 + 1,125 - 200 + 5 = 1,780. Using the moderately active factor: 1,780 x 1.55 = about 2,760 calories per day.

Most people overestimate their activity level. If you are unsure between two categories, choose the lower one. A single hour at the gym does not offset an otherwise sedentary day, and fitness trackers can overstate exercise calories.

How your number compares with general guidelines

The Dietary Guidelines for Americans give broad estimated calorie needs for adults of roughly 1,600 to 2,400 calories a day for women and 2,000 to 3,000 for men, depending on age and activity. Needs tend to be higher in younger, larger and more active people and lower in older, smaller and less active people.

These ranges are useful as a sanity check. If your calculation gives a number far outside them, double-check your inputs, especially your units and activity level. A personal calculation is still more useful than a population average, because it reflects your actual size and routine.

Step 3: Adjust for your goal

To maintain your weight, eat close to your TDEE. To lose weight, eat less than your TDEE. A daily deficit of about 300–500 calories is a common starting point that most people can sustain while keeping energy and training performance reasonable. In the first example, that would put the woman at roughly 1,420–1,620 calories per day.

To gain muscle, eat slightly more than your TDEE, typically 250–500 calories above maintenance, and combine it with progressive strength training. A smaller surplus tends to mean less fat gain alongside the muscle. Using the second example, the man would aim for roughly 3,000–3,250 calories.

Whatever your goal, protein matters. Research on resistance training suggests that intakes around 1.6 grams per kilogram of body weight per day support muscle gain, and many people aim for a similar or slightly higher amount while dieting to help preserve muscle.

How low is too low

Bigger deficits produce faster weight loss on paper, but they are harder to stick with and make it more difficult to get enough protein, fiber, vitamins and minerals. They can also increase muscle loss, fatigue and hunger.

A common rule of thumb is that women should not go below about 1,200 calories a day and men below about 1,500 without medical supervision. Very-low-calorie diets, usually defined as under 800 calories a day, should only be followed under the care of a doctor.

If you are pregnant or breastfeeding, under 18, have diabetes or another medical condition, take medications that affect appetite or blood sugar, or have a history of disordered eating, talk to a doctor or registered dietitian before setting a calorie target.

Test your estimate against real results

Every equation is an educated guess. Individual metabolic rates can differ noticeably from the predicted value, so treat your number as a starting point and let your own data refine it.

Eat at your target consistently for two to three weeks while tracking your intake as accurately as you can. Weigh yourself under the same conditions several times a week, for example in the morning after using the bathroom, and compare weekly averages rather than single readings. Daily weight can swing by a kilogram or more from water, salt and food volume alone.

If your weekly average is not moving in the direction you want, adjust your intake by about 100–200 calories and reassess after another two weeks. If you are losing much faster than planned, add some calories back. A food tracker such as the Goby AI app, which shows calories when you scan a product barcode, can make the logging part of this process quicker.

When to recalculate

Your needs are not fixed. As you lose weight, your body requires less energy to maintain and move a smaller frame, so a deficit that worked at the start will shrink over time. Recalculate after every 4–5 kg (about 10 pounds) of change, or whenever progress stalls for several weeks.

Also recalculate when your routine changes substantially, such as starting a new sport, switching to a more physical job, recovering from an injury or getting older. Small, regular updates keep your target realistic.