Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to maintain life-sustaining functions — breathing, heartbeat, brain function, cell repair. It represents 60-75% of total daily energy expenditure and is influenced by age, sex, weight, height, and genetics.

Total Daily Energy Expenditure (TDEE) is your BMR multiplied by an activity factor. It represents all the calories you burn in an average day, including exercise, walking, fidgeting, and digesting food. Eating at your TDEE maintains your current weight.

How accurate is the Mifflin-St Jeor equation?

It is usually treated as a reasonable starting estimate for many adults, often within about ±10% of measured expenditure. Individual factors like genetics, hormones, medication use, and body composition can still shift the real number, so treat the result as a starting point and adjust from real-world results.

How many calories should I eat to lose weight?

A moderate deficit below TDEE is commonly used for weight loss, with roughly 500 calories per day often cited as a practical example. The actual rate varies, and aggressive deficits are harder to sustain and may not be appropriate for everyone.

Why is my TDEE so much higher than my BMR?

Activity can add 20-90% on top of BMR. A sedentary person burns 20% more than BMR; a very active person nearly doubles it. This is why exercise is so effective — it substantially increases calorie burn beyond baseline.

Does metabolism slow with age?

Yes, but less than people think. BMR decreases about 1-2% per decade after age 20, primarily due to loss of muscle mass. Strength training can largely offset this decline by maintaining or building lean tissue.

Should I eat back my exercise calories?

It depends on your goal and on how accurate your exercise-calorie estimate is. Some people keep the original intake target, while others add back part of the session cost. A conservative approach is often easier to manage when wearable estimates are uncertain.

Calorie Calculator

Estimate your daily calorie needs (BMR and TDEE) based on age, gender, height, weight, and activity level. Get targets for weight loss, maintenance, and muscle gain.

Unit System

Age

years

Biological Sex

Weight

Height

Activity Level

BMR (Resting)

1,780 kcal

Calories at complete rest

Maintenance (TDEE)

2,759 kcal

To maintain current weight

Daily Calorie Targets by Goal

Aggressive Loss (~0.68 kg/week)	2,009 kcal
Weight Loss (~0.45 kg/week)	2,259 kcal
Mild Loss (~0.23 kg/week)	2,509 kcal
Maintenance	2,759 kcal
Lean Bulk (+300 kcal)	3,059 kcal
Bulk (+500 kcal)	3,259 kcal

Quick Macro Estimate (at maintenance):

Protein: ~207gCarbs: ~276gFat: ~92g

Planning notes, formulas, and examples

About the Calorie Calculator

How many calories should you eat per day? The answer depends on your age, sex, body size, and how active you are. This calorie calculator uses the Mifflin-St Jeor equation to estimate Basal Metabolic Rate (BMR) and then applies an activity factor to estimate Total Daily Energy Expenditure (TDEE).

Your BMR is the number of calories your body burns at complete rest just to keep you alive: breathing, circulating blood, maintaining body temperature, and repairing cells. It accounts for a large share of daily energy use. Your TDEE adds the calories burned through physical activity, exercise, and the thermic effect of food.

Once you know your estimated TDEE, you can sketch out rough intake ranges for maintenance, fat loss, or weight gain. These numbers are estimates, not prescriptions, so they work best as a starting point that you refine from weight trends and daily function.

When This Page Helps

Guessing your calorie needs often leads to bigger adjustments than necessary. This calculator gives you a structured estimate you can use when starting a new eating plan, returning to training, or reassessing intake after weight has changed.

It is most useful as a baseline. From there, smaller changes in intake or activity are usually easier to judge than trying to restart from scratch each time progress slows.

How to Use the Inputs

Enter your age in years.
Select your biological sex (male/female) — this affects the BMR formula.
Enter your weight in the displayed unit (kg or lbs).
Enter your height in centimeters or feet/inches.
Select the activity level that best describes your typical week.
Review your BMR, maintenance calories (TDEE), and targets for weight loss or gain.

Formula used

Mifflin-St Jeor Equation:
  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

TDEE = BMR × Activity Multiplier
  Sedentary (little/no exercise):    × 1.2
  Lightly active (1-3 days/week):    × 1.375
  Moderately active (3-5 days/week): × 1.55
  Very active (6-7 days/week):       × 1.725
  Extra active (2× per day):         × 1.9

Example Calculation

Result: 2,759 kcal/day (maintenance)

A 30-year-old male, 80 kg, 180 cm, moderately active (exercise 3-5 days/week) has a Mifflin-St Jeor BMR of 1,780 kcal. Multiplied by the moderate activity factor of 1.55, his TDEE is approximately 2,759 kcal/day. A 500 kcal deficit gives about 2,259 kcal/day, while a lean-gain target of +300 kcal/day is about 3,059 kcal/day.

Tips & Best Practices

A calorie deficit of 500 kcal/day leads to roughly 1 pound of fat loss per week. Do not exceed a 1,000 kcal/day deficit without medical supervision.
Protein intake is critical during a calorie deficit — aim for 0.7-1g per pound of body weight to preserve muscle mass.
Recalculate your calories every 10-15 lbs of weight change, as your BMR decreases with weight loss.
If your weight has not changed in 2+ weeks despite following your calorie target, reduce by 100-200 kcal or increase activity by one level.
Meal timing matters less than total daily intake. Whether you eat 2 meals or 6, total calories determine weight change.
Track your food intake for at least 2 weeks to build accuracy. Most people underestimate calories by 20-40%.

Understanding the Mifflin-St Jeor Equation

Published in 1990, the Mifflin-St Jeor equation is one of the most commonly used population-level formulas for estimating resting calorie needs. It uses weight, height, age, and sex to estimate resting energy expenditure, then relies on an activity factor to extend that estimate into daily needs.

Activity Levels Explained

Choosing the right activity level matters as much as choosing the formula. Sedentary usually means very little intentional exercise. Light, moderate, active, and extra active reflect progressively more movement across the week. Many people overestimate this input, so it often helps to start conservatively and adjust from results.

From Estimate to Adjustment

No calorie formula can fully account for daily variation in movement, appetite, training load, or body composition. The most useful approach is to start with the estimate, hold intake steady for a couple of weeks, and then adjust based on weight trend, hunger, energy, and performance.

Sources & Methodology

Last updated: March 28, 2026

Methodology

This worksheet uses the Mifflin-St Jeor equation to estimate resting calories, then applies the selected activity multiplier to estimate TDEE. The loss and gain targets shown on the page are simple adjustments around that TDEE, intended as planning ranges rather than guaranteed outcomes. Real calorie needs can shift with body composition, medication use, illness, training volume, and daily movement.

Sources

A new predictive equation for resting energy expenditure in healthy individuals (American Journal of Clinical Nutrition / PubMed) — Primary source for the Mifflin-St Jeor equation used in the calculator.
Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (National Academies Press) — Reference for energy-planning context and population-level energy needs.

Frequently Asked Questions

Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to maintain life-sustaining functions — breathing, heartbeat, brain function, cell repair. It represents 60-75% of total daily energy expenditure and is influenced by age, sex, weight, height, and genetics.