BMR: Your Baseline Calorie Burn
Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to maintain basic functions (breathing, circulation, cell repair). It's the foundation of all calorie calculations.
The most accurate common formula is the Mifflin-St Jeor equation (validated in multiple studies as more accurate than the older Harris-Benedict formula):
For Men
BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(years) + 5
For Women
BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(years) − 161
Example: 35-year-old woman, 140 lbs (63.5kg), 5'5" (165cm):
BMR = (10 × 63.5) + (6.25 × 165) − (5 × 35) − 161 = 635 + 1,031 − 175 − 161 = 1,330 calories/day
TDEE: Multiplying BMR by Activity Level
Total Daily Energy Expenditure (TDEE) = BMR × Activity Multiplier
| Activity Level | Multiplier | Description |
|---|---|---|
| Sedentary | 1.2 | Desk job, little/no exercise |
| Lightly active | 1.375 | Light exercise 1–3 days/week |
| Moderately active | 1.55 | Moderate exercise 3–5 days/week |
| Very active | 1.725 | Hard exercise 6–7 days/week |
| Extremely active | 1.9 | Very hard exercise + physical job |
Using the example above (BMR = 1,330): moderately active TDEE = 1,330 × 1.55 = 2,062 calories/day
Why Calculators Are Estimates
TDEE formulas are population averages. Individual metabolic variation means any given person's actual TDEE may be ±200 calories (roughly 10%) from what the formula predicts. Factors that affect actual metabolism:
- Muscle mass (more muscle = higher BMR)
- Non-exercise activity thermogenesis (NEAT) — fidgeting, walking around, standing vs. sitting
- Thermic effect of food (digesting protein burns more calories than digesting fat)
- Hormonal factors (thyroid function, cortisol, insulin sensitivity)
How to Calibrate Your Actual TDEE
The most reliable method isn't a formula — it's observation:
- Track everything you eat for 2 weeks while keeping your weight and diet consistent
- Average your daily calorie intake over those 14 days
- If your weight stayed stable, your average intake = your TDEE
- If you gained, your TDEE is slightly lower; if you lost, slightly higher
This calibrated TDEE is more accurate than any formula because it's derived from your actual body's response.
Deficits, Surpluses, and Adaptive Thermogenesis
- Fat loss: −500 calories/day from TDEE ≈ 1 lb/week (theoretical; varies individually)
- Muscle gain: +250–500 calories/day (lean bulk) — enough to support muscle growth without excess fat gain
Important caveat: adaptive thermogenesis. When you eat significantly less than your TDEE for weeks, your body reduces BMR by 10–20% in response (a survival mechanism). This is why "eating less stops working" — your TDEE has dropped. Taking periodic diet breaks at maintenance calories can partially counteract this adaptation.
Using the TDEE Calculator
Use our CalcPeek calorie calculator to calculate your BMR and TDEE based on your measurements and activity level. Then use the calibration method above to fine-tune it for your actual metabolism. Remember that these are starting estimates — observe your actual results over 2–4 weeks and adjust accordingly.