Harris-Benedict BMR Calculator
Enter your sex, age, height, and weight to calculate your Basal Metabolic Rate (BMR) using the Harris-Benedict equation. Choose between the original 1919 formula and the more accurate 1984 Roza-Shizgal revision, then pick your activity level to get your Total Daily Energy Expenditure (TDEE) and calorie targets for maintenance, weight loss, or weight gain. Switch between metric and imperial units instantly.
Formula
Worked example
A 30-year-old male weighing 80 kg at 180 cm (revised formula): BMR = 88.362 + (13.397 × 80) + (4.799 × 180) - (5.677 × 30) = 88.362 + 1071.76 + 863.82 - 170.31 = 1853.6 kcal/day. At a moderate activity level (PAL 1.55): TDEE = 1853.6 × 1.55 = 2873 kcal/day. A 500 kcal/day deficit targets 0.5 kg/week of loss: 2873 - 500 = 2373 kcal/day.
What is Basal Metabolic Rate?
Basal Metabolic Rate (BMR) is the number of calories your body burns in 24 hours of complete rest - no digestion, no movement, just the minimum energy required to keep your heart beating, your lungs breathing, and your cells alive. It accounts for roughly 60-70 percent of total daily calorie burn for most people. BMR is determined mainly by your weight, height, sex, and age, with sex and body composition having the largest influence: men tend to have higher BMR than women of the same weight because they carry proportionally more muscle, and BMR declines gradually with age as lean mass decreases.
The Harris-Benedict equation: original vs. revised
James Arthur Harris and Francis Gano Benedict published the original BMR equation in 1919 after measuring oxygen consumption in 239 subjects. Their formulas were groundbreaking but based on a small and relatively homogeneous sample. In 1984, Roza and Shizgal re-derived the coefficients using a larger dataset and corrected for systematic overestimation in the original, particularly for older and heavier individuals. The revised equation now appears in most clinical nutrition software. Both versions use the same four variables - weight, height, age, and sex - but with different regression coefficients. For most people the two formulas differ by 50-150 kcal/day; for very heavy or very light individuals the gap can be wider, and the revised version is the better choice.
From BMR to Total Daily Energy Expenditure
BMR is the floor, not the ceiling. To estimate how many calories you actually need each day, multiply your BMR by a Physical Activity Level (PAL) factor that reflects how much you move. The sedentary multiplier (1.2) adds only the energy of sitting, digesting food, and light daily movement. The moderately active multiplier (1.55) is appropriate for someone who exercises at moderate intensity three to five days per week. The extra-active multiplier (1.9) suits endurance athletes or people whose jobs involve sustained physical labor. The resulting number - Total Daily Energy Expenditure (TDEE) - is your maintenance calorie level: the intake that holds your weight steady over time. To lose weight, eat below TDEE; to gain, eat above it. A common rule of thumb is that a 500 kcal/day deficit produces roughly 0.5 kg of weight loss per week, though individual results vary with water retention, hormones, and metabolic adaptation.
Accuracy and limitations
The Harris-Benedict equation is a population-level regression, so it gives an estimate, not a guarantee. Studies report a standard error of around 7-10 percent compared with measured resting metabolic rate. That means your true BMR could reasonably be 100-200 kcal higher or lower than the calculator shows. The equation tends to overestimate for people with a high percentage of body fat, because fat tissue is metabolically less active than muscle, and it can underestimate for very muscular individuals. The PAL multipliers add further uncertainty: most people overestimate their activity level, which is the single biggest source of error when using calculated TDEE for weight management. For the most accurate result, track your actual food intake and body weight for two to three weeks, then adjust your calorie target up or down based on the observed trend.
Activity level multipliers (Physical Activity Level)
| Activity level | Description | PAL multiplier | TDEE example (1700 kcal BMR) |
|---|---|---|---|
| Sedentary | Desk work, little or no exercise | 1.20 | 2,040 kcal |
| Lightly active | 1-3 days/week light exercise | 1.375 | 2,338 kcal |
| Moderately active | 3-5 days/week moderate exercise | 1.55 | 2,635 kcal |
| Very active | 6-7 days/week hard exercise | 1.725 | 2,933 kcal |
| Extra active | Hard daily training + physical job | 1.90 | 3,230 kcal |
Standard PAL factors used to multiply BMR into a total daily calorie estimate. Values from Harris-Benedict convention as updated by Roza and Shizgal (1984) and subsequent dietetic practice.
Frequently asked questions
What is the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the calories your body needs at complete rest for 24 hours - no movement, no digestion. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor that accounts for exercise and daily movement. TDEE is the number you use to plan your diet: eating at TDEE maintains weight, eating below it loses weight, eating above it gains weight.
Which formula version should I use - original or revised?
The revised Roza-Shizgal (1984) version is recommended for most people. It was derived from a larger dataset and corrects for the original equation's tendency to overestimate BMR, particularly in older adults and heavier individuals. The original Harris-Benedict (1919) formula is included for historical comparison and for situations where a protocol specifically calls for it.
How accurate is the Harris-Benedict equation?
It is a reasonable estimate, typically within 10 percent of a measured resting metabolic rate for most adults. However, body composition is not captured: two people of the same weight, height, sex, and age can have quite different BMRs if one has substantially more muscle. For clinical precision, a measured indirect calorimetry test is more accurate. For practical weight management, treat the calculated TDEE as a starting point and adjust by 100-200 kcal based on two to four weeks of real-world results.
Why does the formula use different coefficients for men and women?
On average, men carry more lean muscle mass relative to total body weight than women of the same size. Muscle tissue is metabolically more active than fat tissue, so it burns more calories at rest. The separate male and female equations capture this average difference. The equations do not account for individual variation in body composition - a very muscular woman and a sedentary man of the same statistics will both get the same-sex estimate even if their actual BMRs differ significantly.
How do I use this to lose weight?
Start by calculating your TDEE using your accurate weight, height, age, sex, and an honest assessment of your activity level. A deficit of 500 kcal/day below TDEE is the standard clinical starting point and targets roughly 0.5 kg of weight loss per week. A deficit of 250 kcal/day is gentler and more sustainable for people who are close to their goal weight. Avoid cutting below your BMR for extended periods, as very low intakes impair metabolic adaptation and make it harder to meet protein and micronutrient needs.
Does BMR change over time?
Yes, in two main ways. First, BMR declines gradually with age because lean muscle mass tends to decrease - roughly 1-2 percent per decade after age 30. Second, significant changes in body weight shift BMR because a heavier body has more cells to maintain. Strength training to preserve or build muscle is one of the most effective strategies for keeping BMR higher as you age. Re-calculate whenever your weight changes by more than 3-5 kg or your activity level shifts substantially.
What activity level should I choose?
Be honest and pick the lower option when you are unsure. Most people overestimate their activity level, which causes TDEE to be overstated and undermines weight-loss plans. 'Sedentary' fits desk workers who do minimal structured exercise. 'Lightly active' fits 1-3 days per week of genuinely elevated heart rate. 'Moderately active' fits 3-5 days of real effort - not a gentle walk, but a workout where you break a sweat. 'Very active' is for people training hard 6-7 days per week. 'Extra active' is for professional athletes or people with physically demanding jobs on top of daily training.