Energy Requirement Calculator: How to Use It

An energy requirement calculator estimates your total daily energy expenditure (TDEE)—the number of calories you burn each day—based on your age, sex, weight, height, and activity level. You enter those basic details, and the calculator returns your maintenance calories, which is the intake needed to keep your weight stable. From that number, you can adjust for weight loss or gain by adding or subtracting calories.

Formula

The calculator uses the Mifflin-St Jeor equation to find your basal metabolic rate (BMR), then multiplies it by an activity factor. The BMR formula is:

BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + S

where S is +5 for men and −161 for women. The activity factor (1.2 to 1.9) represents how much you move beyond resting. Total daily energy expenditure is then:

TDEE = BMR × activity factor

All results are in kilocalories per day (kcal/day), the same unit as food labels.

Worked Example

Using the default inputs: a 30-year-old man, 70 kg, 170 cm, moderately active.

1. BMR = 10×70 + 6.25×170 − 5×30 + 5 = 700 + 1062.5 − 150 + 5 = 1617.5 kcal/day
2. TDEE = 1617.5 × 1.55 = 2507.125 ≈ 2507 kcal/day

The calculator shows 2507 kcal/day, matching the result above.

What the Result Means

Your TDEE is the number of calories you burn on a typical day. If you eat that many calories, your weight stays roughly the same. To lose weight, you need a calorie deficit—eating fewer calories than your TDEE. A deficit of 500 kcal/day typically leads to about 0.45 kg (1 lb) of fat loss per week, though individual results vary. To gain weight, you eat above your TDEE, ideally with strength training to build muscle rather than just fat.

Remember that this is an estimate. Real-world metabolism varies by genetics, muscle mass, and even sleep. Use the number as a starting point, then adjust based on your weight trend over a few weeks.

How to Choose Your Activity Level

Choosing the right activity factor is the most common source of error. Be honest—most people overestimate their activity.

• Sedentary (1.2): desk job, little or no exercise
• Light (1.375): exercise 1–3 times per week
• Moderate (1.55): exercise 3–5 times per week
• Active (1.725): hard exercise 6–7 times per week
• Very active (1.9): physically demanding job plus daily training

If you’re unsure, pick the lower option. It’s easier to adjust upward than to cut calories drastically later.

Common Mistakes and Limitations

Several errors can make your result inaccurate:

• Using pounds and inches without converting: The formula requires kg and cm. If you enter pounds, the result will be wildly wrong. Convert: 1 lb = 0.4536 kg, 1 inch = 2.54 cm.
• Overestimating activity: A 30-minute walk three times a week is light, not moderate.
• Ignoring body composition: A muscular person burns more calories than a person with higher body fat at the same weight. The formula doesn’t account for this.
• Rounding too early: Keep decimals until the final answer to avoid accumulating error.

The Mifflin-St Jeor equation is accurate for most adults, but it’s less reliable for athletes, very obese individuals, and older adults. It also assumes average body composition; it doesn’t know your muscle-to-fat ratio.

Alternatives to This Calculator

If you need a different estimate, consider these methods:

• Harris-Benedict equation: An older formula that tends to overestimate by about 5%.
• Katch-McArdle formula: Uses lean body mass instead of total weight, so it’s better for athletes if you know your body fat percentage.
• Indirect calorimetry: A medical test that measures your oxygen use and carbon dioxide production. It’s the gold standard but requires special equipment.

For most people, the Mifflin-St Jeor equation is the best balance of accuracy and simplicity.

Frequently Asked Questions

How many calories should I eat to lose weight?

Subtract 500–1000 kcal from your TDEE for a loss of 0.45–0.9 kg (1–2 lb) per week. Don’t go below 1200 kcal/day for women or 1500 for men without medical supervision.

Do I need to eat back exercise calories?

Most people don’t need to. The activity factor already includes exercise. Only if you do an unusually long or intense workout and feel weak should you add a small snack, not the full estimated burn.

Is the result the same as my BMR?

No. BMR is the calories you burn at rest, just to keep your heart beating and lungs breathing. TDEE includes all daily movement and exercise. Your TDEE is always higher than your BMR unless you’re bedridden.

Can I use this for a child or teenager?

The formula is designed for adults. Children’s energy needs vary with growth spurts, so consult a pediatrician or dietitian instead.

Why does my fitness tracker show a different number?

Trackers estimate based on your heart rate and movement, but they often overestimate calories burned. Use your tracker’s number as a relative guide, not an exact measure.

How often should I recalculate?

Recalculate after a 5 kg (11 lb) weight change or if your activity level changes significantly. Otherwise, adjust your intake based on your weight trend.

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in age | Age | years | 30 | 18
in sex | Sex | Male=1, Female=0.9 | 1 | 0
in weight | Weight | kg | 70 | 30
in height | Height | cm | 170 | 120
sel activity | Activity level | Sedentary=1.2, Light=1.375, Moderate=1.55, Active=1.725, Very active=1.9 | 1.55
out tdee | Total daily energy expenditure | kcal/day | (10 * weight + 6.25 * height - 5 * age + 5) * activity | 0
out bmr | Basal metabolic rate | kcal/day | 10 * weight + 6.25 * height - 5 * age + 5 | 0