Introduction
Effective weight management comes down to understanding calories in vs. calories out. To plan for weight loss, one must first estimate how many calories the body requires to maintain its weight (daily energy needs) and then determine an appropriate calorie deficit to lose weight at a safe rate.
This guide outlines the standard evidence-based methodology for:
Estimating Basal Metabolic Rate (BMR) using the Mifflin-St Jeor equation
Calculating Total Daily Energy Expenditure (TDEE) with physical activity multipliers
Setting calorie deficits for weight loss (~3,500 kcal ≈ 1 pound of fat), with examples in both pounds and kilograms
It also highlights the minimum safe calorie intakes (about 1,200 kcal for women and 1,500 kcal for men) recommended by health authorities to ensure nutritional needs are met. All formulas and targets are supported by scientific and clinical guidelines and can also be used for estimating maintenance or weight gain plans.
Estimating BMR with the Mifflin-St Jeor Equation
Basal Metabolic Rate (BMR)—also called Resting Energy Expenditure (REE)—is the number of calories your body burns at rest to support basic functions like breathing, circulation, and cell repair.
The Mifflin-St Jeor equation is the preferred formula for estimating BMR in healthy adults and is widely used in clinical nutrition due to its accuracy, especially in individuals with higher body weights.
Mifflin-St Jeor BMR Equation
Estimated BMR (kcal/day):
Men:
10 × weight (kg) + 6.25 × height (cm) – 5 × age (yr) + 5
(e.g., 80 kg, 180 cm, 30 years old → ~1,759 kcal/day)Women:
10 × weight (kg) + 6.25 × height (cm) – 5 × age (yr) – 161
(e.g., 65 kg, 165 cm, 30 years old → ~1,417 kcal/day)
These values represent resting calorie burn and serve as the foundation for calculating daily energy needs.
Total Daily Energy Expenditure (TDEE) and Activity Multipliers
TDEE is the total number of calories burned per day, including both BMR and physical activity. It’s calculated by multiplying BMR by a Physical Activity Level (PAL) factor:
Activity Level | Description | Multiplier |
Sedentary | Little or no exercise (desk job) | 1.2 |
Lightly active | Light exercise 1–3 days/week | 1.375 |
Moderately active | Moderate exercise 3–5 days/week | 1.55 |
Active | Hard exercise 6–7 days/week | 1.725 |
Very active (extra) | Intense exercise daily or physical job | 1.9 |
Example:
If BMR = 1,600 kcal/day and activity level is moderately active (×1.55):
TDEE = 1,600 × 1.55 = 2,480 kcal/day
TDEE represents your maintenance calorie level—the number of calories needed to maintain your current weight.
Calorie Deficits for Weight Loss (The 3,500 kcal Rule)
To lose weight, you need to consume fewer calories than your TDEE. A common rule is that 3,500 kcal ≈ 1 pound of fat.
Examples of standard daily calorie deficits:
~1 lb/week (≈0.45 kg/week): 500 kcal/day deficit = 3,500 kcal/week
~2 lbs/week (≈0.9 kg/week): 1,000 kcal/day deficit = 7,000 kcal/week
~0.5 kg/week (≈1.1 lbs/week): 550 kcal/day deficit = ~3,850 kcal/week
~1 kg/week (≈2.2 lbs/week): 1,100 kcal/day deficit = ~7,700 kcal/week
To calculate your own target:
Daily deficit = Total weekly calorie deficit ÷ 7
While this rule is a helpful planning guideline, actual weight loss may vary due to factors like metabolism, water retention, and adaptive thermogenesis.
The same methodology can be used for weight maintenance (TDEE) or weight gain (TDEE + surplus).
Safe Minimum Calorie Intake Levels
When reducing calories, it's important not to go too low. Extreme calorie restriction can lead to nutrient deficiencies, fatigue, and hormonal issues.
Health authorities recommend minimum daily intakes of:
~1,200 kcal/day for women
~1,500 kcal/day for men
These thresholds ensure adequate nutrition, even while in a deficit. Diets below these levels should only be followed under medical supervision.
Note: Some individuals—especially smaller or less active women—should aim for smaller deficits (e.g., 250–500 kcal/day) to remain above the minimum safe intake.
Summary
The Mifflin-St Jeor → TDEE → Calorie Deficit approach is a science-backed, practical framework used by dietitians and clinicians worldwide. It helps:
Estimate daily calorie needs accurately
Set appropriate and safe weight loss targets
Ensure nutritional adequacy during a calorie deficit
By following this structured approach—and not going below recommended minimums—you can achieve weight loss safely and effectively.