Energy Expenditure Calculator: How It Works

An energy expenditure calculator estimates the total calories you burn per day based on your age, sex, weight, height, and activity level. You enter those details and the calculator returns your Total Daily Energy Expenditure (TDEE) in kilocalories, which is the sum of your resting metabolic rate and the calories burned through physical activity. This number is the starting point for weight management: eat below it to lose weight, above it to gain, and at it to maintain.

Formula

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

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

where S is +5 for men and −161 for women. Then:

TDEE = BMR × activity factor

The activity factors are: 1.2 for sedentary (little or no exercise), 1.375 for light activity (1–3 days per week), 1.55 for moderate (3–5 days), 1.725 for active (6–7 days), and 1.9 for very active (hard exercise daily or physical job). All results are in kilocalories per day, which are the same as the “calories� on food labels.

Worked Example

Using the default values from the calculator: age 30, male, weight 70 kg, height 170 cm, moderate activity (factor 1.55).

1. Calculate BMR: 10 × 70 = 700; 6.25 × 170 = 1062.5; 5 × 30 = 150. So BMR = 700 + 1062.5 − 150 + 5 = 1617.5 kcal/day.
2. Multiply by activity factor: 1617.5 × 1.55 = 2507.125.
3. Round to the nearest whole number: 2507 kcal/day.

This matches the calculator’s output for the defaults.

What the Result Tells You

Your TDEE is the number of calories your body uses in a typical day. It includes the energy for basic functions like breathing, circulation, and cell repair (BMR) plus the extra energy for walking, exercising, digesting food, and all movement. If you consume roughly this many calories, your weight should stay stable. To lose weight, you need a calorie deficit—typically 300–500 kcal/day for slow, sustainable loss. To gain weight, you need a surplus. Keep in mind that the result is an estimate; individual variation can be ±10% due to genetics, muscle mass, and other factors.

Common Mistakes and Limitations

• Mixing units: The formula requires weight in kilograms and height in centimeters. If you use pounds and inches, convert first: 1 lb = 0.4536 kg, 1 inch = 2.54 cm.
• Overestimating activity: Many people choose “moderateâ€� when they are actually sedentary. If you sit most of the day and exercise lightly 1–2 times a week, choose “lightâ€� or “sedentary.â€�
• Rounding too early: Do all calculations with full precision, then round at the end. Rounding intermediate steps can change the result by 10–20 kcal.
• Using it for medical purposes: The Mifflin-St Jeor equation is a general estimate, not a clinical measurement. It does not account for body composition, medical conditions, or medications. Consult a healthcare professional for personalized advice.

How to Choose an Activity Factor

Picking the right activity factor is the biggest source of error. Use these descriptions as a guide:

• Sedentary (1.2): Desk job, no exercise, mostly sitting.
• Light (1.375): Light exercise 1–3 days per week, or a job that involves some standing.
• Moderate (1.55): Moderate exercise 3–5 days per week, or a job with regular walking.
• Active (1.725): Hard exercise 6–7 days per week, or a physically demanding job.
• Very active (1.9): Intense daily exercise plus physical work, or two-a-day training.

If you are between two levels, choose the lower one. Most people overestimate their activity, which leads to a TDEE that is too high and weight loss that is slower than expected.

Alternatives and Related Calculations

The Mifflin-St Jeor equation is one of several BMR formulas. The Harris-Benedict equation (revised in 1984) is older and tends to overestimate BMR by about 5%. The Katch-McArdle formula uses lean body mass instead of total weight, which is more accurate for athletes but requires knowing body fat percentage. For weight loss, you might also use a BMR calculator to find your resting needs, then add exercise calories separately. Some people use a step counter or fitness tracker to estimate activity calories, but those devices have their own error margins.

Practical Tips for Using the Result

• Track your weight for 1–2 weeks while eating what you think is your TDEE. If your weight stays stable, the estimate is close. If it drifts, adjust by 100–200 kcal.
• Re-calculate after significant weight changes (more than 5 kg) because your BMR changes as your weight changes.
• Use the same calculator consistently rather than switching between formulas, so changes over time are comparable.
• Remember that “calories burnedâ€� from exercise is separate from your TDEE; the activity factor already includes your typical exercise.

Frequently Asked Questions

What’s the difference between BMR and TDEE?

BMR is the calories your body burns at complete rest, just to keep you alive. TDEE is BMR plus all the energy for movement, digestion, and daily activities. The calculator shows both: BMR is the base, and TDEE is the number to use for weight management.

Is the Mifflin-St Jeor formula accurate?

It is considered the most accurate general equation for most adults, with an error of about ±10% compared to laboratory measurements. It works best for people with average body composition. For very muscular or very obese individuals, formulas based on lean body mass may be better.

Should I eat exactly my TDEE to maintain weight?

Yes, in theory. In practice, the estimate may be off, so monitor your weight for a few weeks. If you maintain your weight, you’ve found your maintenance level. If not, adjust your intake by 100–200 kcal per day.

Can I use this calculator if I’m pregnant or breastfeeding?

The formula does not account for the extra energy needs of pregnancy or lactation. Pregnant and breastfeeding women should consult a healthcare provider for appropriate calorie targets, as needs are significantly higher.

Why do I get different results from other calculators?

Other calculators may use a different BMR equation (like Harris-Benedict), different activity factors, or round differently. The Mifflin-St Jeor equation is the most common modern standard, but differences of 100–200 kcal are normal between formulas.

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in age | Age | years | 30 | 18
in sex | Sex | Male=5, Female=-161 | 5 | 0
in weight | Weight | kg | 70 | 30
in height | Height | cm | 170 | 100
in act | Activity level | Sedentary=1.2, Light=1.375, Moderate=1.55, Active=1.725, Very active=1.9 | 1.55 | 0
out tdee | Total daily energy expenditure | kcal/day | ((10 * weight) + (6.25 * height) - (5 * age) + sex) * act | 0
out bmr | Basal metabolic rate | kcal/day | (10 * weight) + (6.25 * height) - (5 * age) + sex | 0