How TDEE Is Calculated

Summary

Total Daily Energy Expenditure (TDEE) estimates how many calories you burn per day, including your resting metabolism and physical activity. It is calculated by first estimating your Basal Metabolic Rate (BMR) — the energy your body uses at complete rest — and then multiplying by an activity factor that accounts for your daily movement and exercise.

The NHS general guidance is approximately 2,500 kcal/day for an average adult man and 2,000 kcal/day for an average adult woman, but individual needs vary substantially depending on age, body size, and activity level.

How it works

1. Estimate BMR using one of two validated equations (Mifflin-St Jeor or Harris-Benedict).
2. Multiply by an activity factor based on your weekly exercise frequency and intensity.

The Mifflin-St Jeor equation (1990) is recommended by the Academy of Nutrition and Dietetics as the most accurate for healthy adults. The Harris-Benedict equation (1919, revised by Roza & Shizgal in 1984) is the older alternative — it may overestimate by approximately 5% compared to Mifflin-St Jeor.

The formula

Step 1: BMR (Mifflin-St Jeor, 1990)

Step 1 (alternative): BMR (Harris-Benedict, revised 1984)

Male: BMR = 88.362 + 13.397W + 4.799H - 5.677A

Female: BMR = 447.593 + 9.247W + 3.098H - 4.330A

Step 2: TDEE

Activity multipliers

These are known as the Katch-McArdle activity factors, widely adopted by ISSA, NASM, ACE and other certification bodies.

Worked example

Inputs explained

• Weight — body weight in kg (or lbs in imperial mode; converted to kg internally using 1 lb = 0.453592 kg).
• Height — height in cm (or inches in imperial mode; converted to cm using 1 in = 2.54 cm).
• Age — age in years. BMR decreases with age due to loss of lean mass.
• Sex — biological sex affects BMR. Males typically have higher BMR due to greater lean body mass.
• Activity level — how often and how intensely you exercise. This is the biggest variable after BMR.
• BMR formula — Mifflin-St Jeor (recommended, 1990) or Harris-Benedict (revised 1984). Most people should use Mifflin-St Jeor.

Outputs explained

• TDEE — your estimated total daily energy expenditure in kcal/day. This is the headline number.
• BMR — your basal metabolic rate in kcal/day. This is what your body would burn at complete rest.
• Weekly calories — TDEE × 7, useful for weekly meal planning.
• Activity comparison table — your BMR multiplied by each activity level, so you can see how your TDEE changes if you exercise more or less.
• Calorie targets — TDEE ± 500 kcal for approximate 0.5 kg/week weight loss or gain (based on the commonly used 3,500 kcal ≈ 0.45 kg body fat approximation).

Assumptions & limitations

• BMR equations are population averages. Individual metabolic rates can vary by ±10-15% due to genetics, body composition, and other factors. Indirect calorimetry is the gold standard for measuring true BMR.
• Activity multipliers are subjective. People tend to overestimate their activity level. When in doubt, choose one level lower.
• Does not account for body composition. Two people of the same weight, height, age, and sex may have very different BMRs if one is muscular and the other is not. The Katch-McArdle formula (not included here) uses lean body mass for this reason.
• Not suitable for children under 15 or pregnant/breastfeeding women, who have different metabolic requirements.
• Weight change targets (±500 kcal) are simplified. The “3,500 kcal = 1 lb” rule is an approximation; actual weight change depends on metabolic adaptation over time.

Verification

All values verified by hand calculation against the original published formulas.