How Many Calories Do You Need a Day?

“How many calories should I eat?” is the first question almost everyone asks when they start tracking. There is a useful answer, a range you can start from, and a precise answer, which only your own body can give you after a few weeks of logging.

The useful answer: published ranges

The U.S. Dietary Guidelines for Americans publish estimated calorie needs for adults by sex, age and activity level. Simplified, they look like this:

“Sedentary” means only the light activity of daily life. “Moderately active” adds the equivalent of walking about 1.5 to 3 miles a day at a brisk pace; “active” means more than that. These are averages for people of typical height and weight, so a tall, heavy or very muscular person will need more, and a small person less.

The better answer: estimate your own maintenance

A calculator gives you a personal starting point by estimating two things:

1. Basal metabolic rate (BMR), the energy your body uses at rest. The most widely used equation for healthy adults is Mifflin-St Jeor, which uses your weight, height, age and sex.
2. Activity, applied as a multiplier from about 1.2 (desk job, little exercise) to 1.9 (physical job plus training).

BMR multiplied by activity gives your total daily energy expenditure (TDEE), the intake at which your weight should hold steady. Most tracking apps do this calculation when you set a goal.

A worked example

The Mifflin-St Jeor equation is:

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

For a 35-year-old woman who is 165 cm tall and weighs 70 kg:

10 × 70 + 6.25 × 165 − 5 × 35 − 161 = 700 + 1,031 − 175 − 161 ≈ 1,395 calories (BMR)

She works at a desk and walks or exercises lightly three times a week, so she uses the “lightly active” multiplier of 1.375:

1,395 × 1.375 ≈ 1,920 calories a day (estimated maintenance)

For a 40-year-old man who is 180 cm and 85 kg and exercises moderately: 850 + 1,125 − 200 + 5 = 1,780 BMR, × 1.55 ≈ 2,760 calories a day.

Activity levels

Two warnings. First, people usually overestimate their activity; when in doubt, choose the lower level. Second, even the best equations predict resting metabolism within about 10% for most people, not exactly.

The precise answer: your own data

The way to find your real maintenance number is simple and slightly tedious:

1. Log everything you eat for two to four weeks without trying to change it.
2. Weigh yourself several mornings a week and look at the weekly average, not single days.
3. If your weight trend is flat, your average intake is your maintenance. If it is rising or falling, adjust accordingly: a steady change of half a kilogram a week corresponds to roughly 550 calories a day above or below maintenance.

Some tracking apps now do this arithmetic for you with an adaptive target that updates from your intake and weight trend.

From maintenance to a goal

• To lose weight, eat below maintenance. A deficit of 300 to 500 calories a day is a sustainable starting point for most people.
• To gain muscle, eat slightly above maintenance (around 250 to 500 calories) alongside strength training and enough protein.
• To maintain, eat about your maintenance and check the trend every few weeks.

Very low intakes are hard to sustain and make it difficult to meet nutrient needs. Many clinicians avoid going below about 1,200 calories a day for women or 1,500 for men without supervision.

What the numbers look like

Using the same equation, here are rough maintenance estimates for lightly active adults of average build. They are illustrations, not prescriptions:

The fall with age in the table is only the equation’s age term. In real life, much of the change comes from losing muscle and moving less, which strength training and an active routine can slow.

When the estimate seems wrong

If you eat at your calculated maintenance for three or four weeks and your weight trend moves steadily in one direction, trust the scale over the equation. People with more muscle, very active jobs or unusual body sizes often sit well outside the averages. Adjust by 100 to 200 calories at a time and re-check after a few weeks. The guide to weight loss plateaus covers what to check before changing a target.

Things that change your needs

• Age: needs tend to fall gradually, partly because of lower muscle mass and activity.
• Body size and composition: larger bodies and more muscle use more energy.
• Activity: the biggest variable you control, including everyday movement, not just workouts.
• Pregnancy and breastfeeding: needs rise; set targets with a clinician.

The bottom line

Use the published ranges to sanity-check, a calculator to get a personal starting point, and two to four weeks of your own logs and weigh-ins to find the real number. Then adjust your target from there.

Related guides: Protein for weight loss · Calorie tracking for beginners · Calorie tracking glossary