How Many Calories Should You Eat Per Day?

By the iCalculateFast Editorial Team · Health · Published June 18, 2026 · 7 min read

The question of how many calories you should eat per day has a frustratingly accurate answer: it depends. It depends on your weight, height, age, sex, and daily activity level. The 2,000-calorie reference number printed on nutrition labels is a population average, not a prescription. A sedentary 120-pound woman needs approximately 1,600 calories to maintain weight. An active 200-pound man needs approximately 3,000. Using the generic 2,000-calorie figure for either individual produces significantly wrong targets. Here is the science-backed formula for calculating yours.

BMR: The Starting Point

Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest — the energy required to maintain basic physiological functions: breathing, circulation, cellular repair, temperature regulation. BMR accounts for approximately 60–75% of total daily calorie expenditure for sedentary to lightly active individuals.

The most accurate formula for estimating BMR in non-athlete adults is the Mifflin-St Jeor equation, developed in 1990 and validated as the most accurate predictor of resting metabolic rate in a 2005 meta-analysis published in the Journal of the American Dietetic Association. The formula:

For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161

Example: a 35-year-old woman who weighs 145 pounds (65.8 kg) and is 5'5" (165 cm) tall: BMR = (10 × 65.8) + (6.25 × 165) − (5 × 35) − 161 = 658 + 1,031 − 175 − 161 = 1,353 calories per day at rest.

TDEE: What You Actually Burn

Total Daily Energy Expenditure (TDEE) is your BMR multiplied by an activity factor that accounts for how much you move throughout the day. TDEE is the number of calories you need to maintain your current weight:

Activity Level	Description	Multiplier
Sedentary	Desk job, no exercise	BMR × 1.2
Lightly active	Light exercise 1–3 days/week	BMR × 1.375
Moderately active	Moderate exercise 3–5 days/week	BMR × 1.55
Very active	Hard exercise 6–7 days/week	BMR × 1.725
Extra active	Physical job + daily exercise	BMR × 1.9

Continuing the example above (BMR = 1,353): if she has a desk job and exercises 3 days per week (lightly active), her TDEE = 1,353 × 1.375 = 1,860 calories per day. This is the maintenance calories target — consuming 1,860 calories per day should hold her weight stable.

Calorie Targets for Weight Loss, Maintenance, and Muscle Gain

Once you know your TDEE, creating a calorie target for a specific goal is straightforward:

Weight loss: a 500-calorie daily deficit produces approximately 1 pound of fat loss per week (since 3,500 calories ≈ 1 pound of fat). For the example above: 1,860 − 500 = 1,360 calories/day for ~1 lb/week loss.
Aggressive weight loss: a 750–1,000 calorie deficit targets 1.5–2 lb/week. Generally not recommended for sustained periods without medical supervision due to muscle loss risk.
Weight maintenance: eat at TDEE — 1,860 calories for the example.
Muscle gain (lean bulk): a 250–500 calorie surplus combined with progressive resistance training supports muscle synthesis. For the example: 1,860 + 300 = 2,160 calories/day.

Why Eating Too Few Calories Backfires

Severe calorie restriction — typically defined as eating below 1,200 calories per day for women or 1,500 for men — triggers adaptive thermogenesis: a metabolic slowdown where your body reduces BMR to conserve energy. Research shows reductions of 15–30% in resting metabolic rate during very-low-calorie diets, which significantly diminishes the calorie deficit and slows weight loss progress.

Simultaneously, extreme restriction increases muscle catabolism (muscle breakdown for energy) and hormonal adaptations that increase hunger and decrease satiety. The practical result is that most people on very low calorie diets lose significant lean muscle mass, experience intense hunger, and regain weight rapidly after returning to normal eating — often ending up at a higher body fat percentage than before dieting, because the regained weight is predominantly fat while lost muscle is not recovered as quickly.

Protein, Carbohydrates, and Fats: Macro Split Guidance

Once you have a calorie target, allocating those calories across macronutrients optimizes both body composition and satiety:

Protein: 0.7–1.0 gram per pound of body weight daily is the range supported by research for muscle retention during weight loss and muscle synthesis during a surplus. Protein is the most satiating macronutrient per calorie, making higher protein diets easier to sustain.
Fat: a minimum of 0.35 grams per pound of body weight is needed for hormonal function and fat-soluble vitamin absorption. Fat should not be aggressively restricted below this level.
Carbohydrates: fill remaining calories with carbohydrates, which are the preferred energy source for the brain and during exercise. Lower carbohydrate intake is a reasonable dietary preference but not a metabolic necessity for most healthy adults.

Calculate Your Personal Calorie Target

Our Calorie Calculator uses the Mifflin-St Jeor formula to calculate your BMR and TDEE based on your weight, height, age, sex, and activity level — then displays calorie targets for weight loss, maintenance, and muscle gain. Your result is personalized to your specific measurements, not a generic population average.

Calorie FAQs

Why did my weight loss stall after a few weeks?

As you lose weight, your body gets smaller and cheaper to run — a 180-pound version of you burns fewer calories than the 200-pound version did, at rest and during activity. A deficit that produced steady loss at your old weight gradually shrinks toward zero. The fix is mechanical, not moral: recalculate your needs every 10–15 pounds and adjust your intake or activity to restore the gap.

Should I eat back the calories my watch says I burned?

Be skeptical. Wrist-based trackers routinely overestimate exercise burn by 20–90% in validation studies, and your calculated TDEE already includes an activity allowance. Eating back the full watch number frequently erases the entire deficit. A safer rule: eat back no more than half of estimated exercise calories, and let two to three weeks of scale trend data tell you whether the budget is actually right.

Sources & References

Try the free Calorie Calculator to run these numbers for your own situation. You can also browse all of our health calculators — every tool works instantly in your browser with no sign-up — explore more research-backed guides on our blog index, or start from the full calculator directory.

Medical disclaimer: This article is for informational and educational purposes only and is not medical advice, diagnosis, or treatment. Formulas used here are population-level estimates that cannot account for your individual medical history. Consult a licensed healthcare provider before changing your diet, exercise, sleep, or medication routine. See our full Disclaimer.