Methodology: How Our Calorie Deficit Calculator Works
This page explains every formula, multiplier, and assumption used by our calculator. We believe in full transparency.
Mifflin-St Jeor Equation
Our calculator uses the Mifflin-St Jeor equation, published in 1990, to estimate Basal Metabolic Rate (BMR). This equation is widely considered one of the most accurate predictive equations for healthy adults.
For men:
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
For women:
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
BMR represents the number of calories your body burns at complete rest to maintain basic life functions such as breathing, circulation, and cell production.
Total Daily Energy Expenditure (TDEE)
TDEE estimates your total daily calorie burn including physical activity. It is calculated by multiplying BMR by an activity factor.
TDEE = BMR × Activity Factor
| Activity Level | Description | Multiplier |
|---|---|---|
| Sedentary | Little or no exercise, desk job | 1.20 |
| 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 |
| Extra active | Very hard exercise + physical job | 1.90 |
Unit Conversions
All inputs are converted to metric units (kg, cm) before formulas are applied. We use precise conversion constants:
- 1 pound = 0.45359237 kilograms
- 1 inch = 2.54 centimeters
- 1 foot = 30.48 centimeters
BMI Calculation
Body Mass Index is calculated using the standard formula:
BMI = weight in kg / (height in meters)²
BMI categories: Underweight (<18.5), Normal (18.5–24.9), Overweight (25–29.9), Obesity (≥30). BMI is a screening measure and does not directly measure body fat.
Calorie Deficit
A calorie deficit occurs when you consume fewer calories than your TDEE. Our calculator offers three deficit levels:
- Small deficit: 250 kcal/day — gradual, sustainable weight loss
- Moderate deficit: 500 kcal/day — approximately 0.5 kg/week estimated
- Larger deficit: 750 kcal/day — faster, but requires medical supervision
Weight-Loss Projections
Projections are estimates based on the assumption that a daily deficit of approximately 500 kcal leads to roughly 0.5 kg of weight change per week. We explicitly state that actual weight change varies because energy expenditure adapts over time, water weight fluctuates, and individual physiology differs.
Why Results Vary
Predictive formulas estimate population-level energy requirements. Individual energy needs can differ by 10–20% or more due to genetics, body composition, metabolic adaptation, hormonal factors, and measurement error. Always use these estimates as a starting point and adjust based on actual results.
Safety Warnings
Never consume fewer than 1,200 kcal/day for women or 1,500 kcal/day for men without medical supervision. Very low-calorie diets can cause nutrient deficiencies, muscle loss, and other health complications.