The Harris-Benedict equation is one of the oldest and most widely used formulas for estimating how many calories your body burns at rest. Plug in your age, sex, height, weight, and activity level, and the calculator returns two numbers that drive almost every weight-management decision you will ever make: your basal metabolic rate (BMR) and your total daily energy expenditure (TDEE).
BMR is the energy you would burn if you stayed in bed all day — breathing, pumping blood, maintaining body temperature, and running your brain. TDEE multiplies that resting number by an activity factor to estimate the calories you actually burn on a normal day. Whether you want to lose fat, gain muscle, or simply maintain your weight, TDEE is the anchor: eat below it and you lose weight, eat above it and you gain, eat at it and you hold steady.
This calculator uses the revised Harris-Benedict equation published by Roza and Shizgal in 1984, which is the version most modern calorie tools adopt.
How to Use
- Select your Sex — male or female. The equation uses different constants for each sex because, on average, men carry more lean mass per kilogram of body weight.
- Enter your Age in completed years. BMR declines roughly 1–2% per decade after early adulthood, so an accurate age matters.
- Type your Weight in kilograms. If you live in the US, multiply pounds by 0.4536 — for example, 180 lb becomes 81.65 kg.
- Enter your Height in centimeters. Multiply inches by 2.54; a height of 5 feet 10 inches is 70 inches, or 177.8 cm.
- Pick your Activity Level honestly. "Sedentary" means a desk job with little intentional exercise; "light" is 1–3 days of walking or light movement per week; "moderate" is 3–5 structured workouts; "active" is 6–7 days of exercise; "very active" is athletic training or a physically demanding job.
- Read the result card. The highlighted BMR is your resting burn; TDEE is your estimated daily maintenance.
To lose about 0.5 kg (1 lb) per week, subtract roughly 500 kcal from your TDEE. To gain mass, add 250–500 kcal. The calculator also shows both values in kilojoules (multiply by 4.184) and your hourly resting burn.
The Revised Harris-Benedict Formula
The original equation was published by James Arthur Harris and Francis Gano Benedict in 1918, based on measurements of about 230 normal-weight young adults. In 1984, Roza and Shizgal re-estimated the coefficients against a larger and more diverse sample, producing the revised version most calculators use today:
- Men: BMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) − (5.677 × age in years)
- Women: BMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) − (4.330 × age in years)
TDEE is then BMR multiplied by one of five activity factors:
| Activity level | Multiplier |
|---|---|
| Sedentary (little or no exercise) | 1.2 |
| Lightly active (1–3 days/week) | 1.375 |
| Moderately active (3–5 days/week) | 1.55 |
| Very active (6–7 days/week) | 1.725 |
| Extra active (physical job or 2× training) | 1.9 |
Worked example: a 30-year-old man weighing 81.65 kg and standing 177.8 cm tall has a BMR of 88.362 + (13.397 × 81.65) + (4.799 × 177.8) − (5.677 × 30) ≈ 1,865 kcal/day. At a moderate activity level (×1.55), his TDEE is about 2,891 kcal/day. To lose fat, he would target roughly 2,400 kcal/day; to gain, roughly 3,200 kcal/day.
Harris-Benedict vs Mifflin-St Jeor
You may see two equations floating around fitness apps. The Mifflin-St Jeor equation (1990) uses simpler coefficients — men: 10W + 6.25H − 5A + 5; women: 10W + 6.25H − 5A − 161 — and is often cited as slightly more accurate in modern populations. The revised Harris-Benedict tends to run about 2–5% higher than Mifflin-St Jeor in most adults. Both are estimates built on population averages; individual metabolic rate can differ by 10% or more due to genetics, body composition, thyroid function, and recent weight changes. Use whichever your coach or app recommends, and re-check your intake against your actual weight trend after 3–4 weeks.
Examples
Example 1 — A moderately active 30-year-old man. Weight 180 lb (81.65 kg), height 5'10" (177.8 cm). BMR ≈ 1,865 kcal/day; with moderate activity (×1.55), TDEE ≈ 2,891 kcal/day. A 20% deficit targets about 2,310 kcal/day for steady fat loss.
Example 2 — A sedentary 25-year-old woman. Weight 60 kg, height 165 cm. BMR = 447.593 + (9.247 × 60) + (3.098 × 165) − (4.330 × 25) ≈ 1,405 kcal/day; sedentary multiplier ×1.2 gives a TDEE of about 1,686 kcal/day. This is why many women on a sedentary 1,500 kcal diet lose weight predictably.
Example 3 — A very active 40-year-old man. Weight 90 kg, height 180 cm, construction worker. BMR ≈ 88.362 + (13.397 × 90) + (4.799 × 180) − (5.677 × 40) ≈ 1,931 kcal/day; ×1.9 very-active multiplier yields a TDEE near 3,669 kcal/day. People with physically demanding jobs often under-eat and feel exhausted; this example shows why their maintenance number is so much higher.
Example 4 — A beginner lifter aiming to bulk. A 22-year-old woman, 65 kg, 168 cm, training 4 days per week. BMR ≈ 447.593 + (9.247 × 65) + (3.098 × 168) − (4.330 × 22) ≈ 1,474 kcal/day; ×1.55 moderate activity gives TDEE ≈ 2,284 kcal/day. A clean bulk adds 250 kcal, targeting about 2,500 kcal/day.
FAQ
What is the Harris-Benedict equation?
It is a mathematical formula, first published in 1918 and revised in 1984, that estimates your basal metabolic rate — the number of calories your body burns at complete rest. It takes into account your weight, height, age, and sex, and is the foundation of most online BMR and TDEE calculators.
How is BMR different from TDEE?
BMR (basal metabolic rate) is the energy you burn lying motionless all day. TDEE (total daily energy expenditure) multiplies BMR by an activity factor to estimate the calories you actually burn on a normal day, including walking, working, exercising, and digesting food. TDEE is usually 20–90% higher than BMR.
Is the revised Harris-Benedict formula the same as the 1918 original?
No. The 1918 original coefficients (men: 66.5 + 13.75W + 5.003H − 6.755A) were derived from a small sample of young, normal-weight subjects. The 1984 Roza-Shizgal revision re-estimated the coefficients and is considered more accurate for modern adults. This calculator uses the 1984 revised version.
What activity level should I choose?
Be honest. Most people overestimate their exercise and underestimate their sitting time. If you work at a desk and walk 5,000 steps a day, pick "sedentary" (×1.2) or "light" (×1.375). If you lift weights or run 3–5 times per week, "moderate" (×1.55) is right. Only choose "very active" (×1.725 or ×1.9) if you train hard six or seven days a week or do heavy physical labor.
How do I turn BMR/TDEE into a weight-loss target?
A 500 kcal-per-day deficit roughly predicts 0.5 kg (1 lb) of fat loss per week, because 1 kg of body fat stores about 7,700 kcal. Subtract 500 from your TDEE to lose, or add 250–500 to gain lean mass. Never drop below 1,500 kcal/day for men or 1,200 kcal/day for women without medical supervision.
Why does my BMR drop as I lose weight?
Two reasons. First, you weigh less, so the weight term in the equation shrinks. Second, dieting itself suppresses metabolic rate beyond what the formula predicts — a phenomenon called adaptive thermogenesis. This is why weight loss plateaus and why you should re-run this calculator every 5–10 kg lost.
How accurate is the Harris-Benedict equation?
It is a population estimate, not a measurement. Indirect calorimetry (a metabolic cart) is the gold standard and can differ from the formula by 10–15% in either direction. Treat the result as a starting point, then adjust based on your actual weight trend over 3–4 weeks.
Disclaimer
This Harris-Benedict calculator is provided for informational purposes only and is not medical advice. It estimates resting and daily calorie needs from population-average formulas and does not account for medical conditions, medications, pregnancy, eating disorders, thyroid disorders, or individual body composition. Consult a registered dietitian, physician, or qualified health professional before making significant changes to your diet, especially if you have a history of disordered eating, diabetes, cardiovascular disease, or any chronic condition.