Daily Energy Expenditure Calculator: How It Works

A daily energy expenditure calculator estimates the total number of calories you burn in a 24-hour period based on your age, sex, weight, height, and activity level. You enter those personal details, and the calculator returns your estimated maintenance calories—the intake needed to keep your weight stable. This number is the foundation for weight loss, gain, or maintenance plans.

Formula

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

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

where S is +5 for men and −161 for women. Total daily energy expenditure (TDEE) = BMR × activity factor.

Activity factors are standard multipliers: sedentary (little or no exercise) = 1.2, lightly active (light exercise 1–3 days/week) = 1.375, moderately active (moderate exercise 3–5 days/week) = 1.55, very active (hard exercise 6–7 days/week) = 1.725, and extra active (physical job + hard training) = 1.9.

Worked Example

Take the default values: 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 step-by-step result.

How to Read the Result

The TDEE is your maintenance calorie level. If you eat this many calories daily, your weight should remain stable over time. To lose weight, you typically create a deficit of 300–500 kcal per day for gradual loss; to gain weight, you add a surplus of the same magnitude. The result is an estimate—individual variation can be 10% or more due to genetics, body composition, and hormonal factors.

Common Mistakes and Limitations

• Unit mix-ups: Entering weight in pounds and height in inches without converting will produce wildly wrong numbers. Always use kilograms and centimeters, or convert first (1 lb = 0.4536 kg, 1 inch = 2.54 cm).
• Overestimating activity: Most people choose “moderate” when they are actually sedentary. If you sit most of the day and exercise 1–2 times weekly, choose “light” or “sedentary.”
• Rounding too early: Round only the final result, not intermediate steps, to avoid cumulative error.
• Ignoring body composition: Muscle burns more calories than fat. Two people with the same weight and height can have different BMRs if one has more muscle.

The Mifflin-St Jeor equation is accurate for most non-obese adults but may underestimate needs in very muscular individuals and overestimate in elderly or severely obese populations. It is not suitable for children, pregnant or breastfeeding women, or athletes with extreme training loads.

Alternatives and Comparisons

Other equations exist: the Harris-Benedict equation (revised in 1984) is slightly older but still used; the Katch-McArdle formula uses lean body mass and is more accurate for athletes, but requires body fat percentage. The Mifflin-St Jeor is generally preferred by dietitians because it was validated in a modern sample and has lower error rates in normal-weight and overweight adults. For most people, the difference between equations is under 100 kcal/day—small enough that consistency matters more than the exact formula.

Using the Calculator for Goals

Once you have your TDEE, you can set a calorie target. For weight loss, a deficit of 500 kcal/day leads to about 0.45 kg (1 lb) loss per week, assuming all else stays equal. For weight gain, a surplus of 500 kcal/day yields similar gains, though some will be fat. Adjust based on weekly average weight trends rather than daily fluctuations. Recalculate every 5–10 kg of weight change because your BMR changes with weight.

Frequently Asked Questions

What is the difference between BMR and TDEE?

BMR is the calories your body burns at complete rest—just to keep your heart beating, lungs breathing, and cells functioning. TDEE adds the energy cost of all daily activities, from walking to digestion to exercise. The calculator shows both, with TDEE being the number you use for meal planning.

How many calories should I eat to lose weight?

Subtract 300–500 kcal from your TDEE for a sustainable deficit. A 500 kcal deficit typically results in about 0.45 kg (1 lb) of fat loss per week. Avoid going below 1,200 kcal for women or 1,500 kcal for men without medical supervision, as very low intakes can cause nutrient deficiencies and muscle loss.

Why does the calculator ask for sex?

The Mifflin-St Jeor equation includes a constant that differs by sex because men generally have more muscle mass and higher BMR at the same weight and height. The constant (+5 for men, −161 for women) accounts for this average difference. If you are transgender or on hormone therapy, results may be less accurate—use the sex that best matches your hormonal profile.

Can I trust the activity factor?

Activity factors are rough averages. They work well for most people but can be off by 200–400 kcal/day. If you track your intake and weight for two weeks, you can fine-tune your estimate: if your weight stays stable, you have found your true maintenance calories; if it changes, adjust your intake accordingly.

Does age really matter that much?

Yes. The formula subtracts 5 kcal per year of age, so a 60-year-old has a BMR about 150 kcal lower than a 30-year-old with the same weight and height. This reflects the gradual loss of muscle mass and metabolic slowdown that occurs with aging, though staying active can offset much of that decline.

What if I exercise on some days but not others?

Use an average activity level rather than changing your factor daily. For example, if you work out intensely three days a week and are sedentary the rest, choose “lightly active” (1.375) or “moderate” (1.55) depending on the intensity. Your TDEE is a daily average, not a per-day precise number.

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in age | Age | years | 30 | 18
in sex | Sex | Male=5, Female=-161
in weight | Weight | kg | 70 | 30
in height | Height | cm | 170 | 120
in act | Activity level | Sedentary=1.2, Light=1.375, Moderate=1.55, Active=1.725, Very active=1.9
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