About

Basal Energy Expenditure (BEE) quantifies the minimum caloric demand of a human body at complete rest over 24 hours. It accounts for roughly 60 - 75% of Total Daily Energy Expenditure (TDEE). Errors in BEE estimation cascade directly into dietary planning failures: underestimation promotes muscle catabolism, overestimation drives unwanted fat gain. Clinical nutrition protocols (ESPEN, ASPEN) require accurate BEE to set caloric targets for patients in ICU, post-surgical recovery, and metabolic rehabilitation. This calculator implements four peer-reviewed equations - Harris-Benedict Revised (1984), Mifflin-St Jeor (1990), Katch-McArdle (1996), and Schofield/WHO (1985) - so you can cross-reference results and identify which model fits your population profile.

Mifflin-St Jeor is generally preferred for healthy adults within normal BMI ranges. Katch-McArdle requires known body fat percentage but yields superior accuracy for athletes and obese individuals whose lean mass diverges from population averages. The Schofield equations are WHO-endorsed and age-banded, making them suitable for pediatric and geriatric assessment. This tool approximates BEE assuming thermoneutral environment, fasted state, and absence of disease-induced hypermetabolism. Real-world expenditure will be higher due to the thermic effect of food (8 - 15%) and non-exercise activity thermogenesis.

Formulas

Harris-Benedict Revised (1984) for males:

BEE = 88.362 + 13.397 × W + 4.799 × H − 5.677 × A

Harris-Benedict Revised (1984) for females:

BEE = 447.593 + 9.247 × W + 3.098 × H − 4.330 × A

Mifflin-St Jeor (1990):

BEE = 10 × W + 6.25 × H − 5 × A + s

Where s = +5 for males, −161 for females.

Katch-McArdle (1996):

BEE = 370 + 21.6 × LBM

Where LBM = W × (1 − BF100). BF is body fat percentage.

Total Daily Energy Expenditure:

TDEE = BEE × AF

Where W = body weight in kg, H = height in cm, A = age in years, AF = activity factor (1.2 - 1.9), and LBM = lean body mass in kg.

Reference Data

Equation	Year	Best For	Accuracy (SEE)	Requires Body Fat %	WHO Endorsed
Harris-Benedict Original	1919	Historical reference	±14%	No	No
Harris-Benedict Revised	1984	General population	±10%	No	No
Mifflin-St Jeor	1990	Healthy adults, normal BMI	±10%	No	No
Katch-McArdle	1996	Athletes, known body composition	±5 - 8%	Yes	No
Schofield (WHO)	1985	Global populations, age-banded	±10 - 12%	No	Yes

Activity Level	Factor	Description	Example
Sedentary	1.200	Little or no exercise	Desk job, no workouts
Lightly Active	1.375	Light exercise 1 - 3 days/week	Casual walking, yoga
Moderately Active	1.550	Moderate exercise 3 - 5 days/week	Jogging, swimming
Very Active	1.725	Hard exercise 6 - 7 days/week	Competitive training
Extra Active	1.900	Very hard exercise + physical job	Professional athlete, laborer

Schofield Age Band	Male Equation (kcal/day)	Female Equation (kcal/day)
10 - 17 years	17.686 × W + 658.2	13.384 × W + 692.6
18 - 29 years	15.057 × W + 692.2	14.818 × W + 486.6
30 - 59 years	11.472 × W + 873.1	8.126 × W + 845.6
60+ years	11.711 × W + 587.7	9.082 × W + 658.5

Frequently Asked Questions

Use Mifflin-St Jeor for the best validated accuracy in healthy adults with BMI between 18.5 and 40. Harris-Benedict Revised is a reasonable alternative but tends to overestimate by 5-15% in obese individuals. Katch-McArdle requires body fat percentage and should only be used when that value is measured (DEXA, hydrostatic weighing) rather than estimated.

BEE declines approximately 1-2% per decade after age 20 due to sarcopenia (muscle loss). The Harris-Benedict and Mifflin-St Jeor equations include an age coefficient to model this decline. However, they were validated primarily on adults aged 18-65. For individuals over 70 or under 18, the Schofield (WHO) age-banded equations are more appropriate because they were derived from datasets that included those populations.

Each equation was derived from a different study population using indirect calorimetry. Harris-Benedict (1919/1984) used predominantly white American adults. Mifflin-St Jeor (1990) used a more diverse sample including obese subjects. Katch-McArdle isolates lean body mass, removing the confound of fat tissue. Schofield used a global WHO dataset. Discrepancies of 100-300 kcal/day between equations are normal and reflect population variance, not calculation error.

No. BEE measures energy expenditure in a post-absorptive state (10-12 hours fasted). The thermic effect of food adds approximately 8-15% of caloric intake on top of BEE. A mixed diet typically produces ~10% TEF. High-protein diets push TEF toward 15%. TDEE calculations in this tool use activity factors that partially incorporate TEF, but for clinical precision, TEF should be calculated separately.

The equations natively use metric units: weight in kg and height in cm. When you select imperial, this tool converts internally using 1 lb = 0.453592 kg and 1 inch = 2.54 cm before applying any equation. Rounding errors are negligible (less than 0.1 kcal). Always enter your measurements as precisely as possible - a 1 kg error in weight shifts BEE by approximately 10-14 kcal/day.

This tool provides predictive BEE estimates suitable for initial caloric target setting. Clinical protocols (ASPEN 2016) recommend indirect calorimetry as the gold standard for critically ill patients because predictive equations can deviate ±20% in ICU settings due to hypermetabolism, medications, and thermal stress. Use these results as a starting point, then adjust based on nitrogen balance, prealbumin levels, and metabolic cart readings.

Select Lightly Active (1.375) if you exercise 1-3 sessions per week for 30-60 minutes each. The activity factor describes total daily movement, not just exercise. A person who runs for 45 minutes but sits for 10 hours still falls in the Lightly Active to Moderately Active range. Overestimating activity level is the most common source of TDEE error and directly causes unintended caloric surplus.