How Daily Calorie Needs Are Calculated
The Mifflin-St Jeor equation — the formula used by registered dietitians — and how activity level multipliers work.
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The Mifflin-St Jeor Equation
The Mifflin-St Jeor equation, published in 1990 in the American Journal of Clinical Nutrition, is the formula most commonly recommended by registered dietitians and used in clinical practice for estimating Basal Metabolic Rate (BMR) — the number of calories your body burns at complete rest.
For men
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
For women
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
A 2005 study published in the Journal of the American Dietetic Association compared five predictive equations and found the Mifflin-St Jeor equation to be the most accurate for estimating measured resting metabolic rate in both obese and non-obese individuals.
From BMR to TDEE: Activity Multipliers
BMR is the calories burned at rest. Total Daily Energy Expenditure (TDEE) accounts for physical activity. The Harris-Benedict activity multipliers, widely used in nutrition practice, are:
| Activity Level | Multiplier | Description |
|---|---|---|
| Sedentary | × 1.2 | Little or no exercise, desk job |
| 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 |
| Extra active | × 1.9 | Very hard exercise, physical job |
TDEE = BMR × Activity Multiplier. This is the number of calories needed to maintain current weight.
Calorie Deficit and Surplus
One pound of body fat contains approximately 3,500 calories. This figure, derived from research by Max Wishnofsky published in 1958, is widely used as a planning benchmark, though individual variation means actual results differ.
- To lose 1 lb/week: Create a daily deficit of 500 calories below TDEE (500 × 7 = 3,500).
- To lose 0.5 lb/week: Create a daily deficit of 250 calories.
- To gain 1 lb/week: Consume 500 calories above TDEE daily.
Most clinical guidelines recommend a maximum deficit of 500–1,000 calories per day, targeting 1–2 lbs of weight loss per week. Larger deficits increase the risk of muscle loss and nutritional deficiencies.
Limitations of Calorie Calculations
Predictive equations estimate average calorie needs. Individual metabolic rates vary by up to 15% from predicted values due to genetics, hormonal factors, gut microbiome, and other variables. Calorie counts on food labels in the US are permitted to be up to 20% inaccurate under FDA regulations.
These calculations are starting points for planning, not precise measurements. Adjust based on real-world results over 2–4 weeks.
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