How to use the calculator
- Choose your sex and the units you prefer.
- Enter your age, height and weight. The results update as you type.
- Read your basal metabolic rate (BMR): the energy your body would use in a day of complete rest.
- Find the lifestyle that matches yours in the table. The last column is the range of daily energy needs for that level of activity. Most people with office jobs and no regular exercise belong in the first row.
How the estimates are made
Basal metabolic rate
The calculator uses the equation published by Mifflin, St Jeor and colleagues in 1990, derived from 498 healthy adults aged 19 to 78 whose resting energy expenditure was measured by indirect calorimetry. In its simplified form it is 10 × weight in kg + 6.25 × height in cm − 5 × age in years, plus 5 for men or minus 161 for women. The same study found that the older Harris-Benedict equations from 1919 overestimated measured resting energy by 5%. A 2005 systematic review of the four most commonly used equations found Mifflin-St Jeor the most reliable, predicting resting rate within 10% of the measured value in more people, both non-obese and obese, than any other.
From BMR to daily needs
Daily energy expenditure is basal metabolism multiplied by a physical activity level (PAL). Many websites use multipliers of 1.2, 1.375, 1.55 and so on, without saying where they come from. This calculator instead uses the three lifestyle categories in Table 5.3 of the FAO/WHO/UNU report on human energy requirements: sedentary or light activity, PAL 1.40–1.69; active or moderately active, 1.70–1.99; vigorous, 2.00–2.40. Because each category is a range, the result is a range too — which is more honest than a single number that looks precise but depends on a guess about your activity.
The report's examples help place yourself: urban office workers who only occasionally do something physically demanding are in the first category; construction workers, or people who do about an hour of jogging, cycling or sport every day, in the second; people who swim or dance for two hours a day, or do hours of heavy manual labour, in the third. It notes that levels above 2.40 are hard to maintain for long.
Examples
| Person | BMR | Light activity | Moderately active | Vigorous |
|---|---|---|---|---|
| Woman, 30, 165 cm, 60 kg | 1,320 kcal | 1,848–2,231 | 2,244–2,627 | 2,641–3,169 |
| Man, 30, 175 cm, 70 kg | 1,649 kcal | 2,308–2,786 | 2,803–3,281 | 3,298–3,957 |
| Man, 35, 5 ft 9 in, 160 lb | 1,651 kcal | — | — | — |
For the woman in the first row: 10 × 60 + 6.25 × 165 − 5 × 30 − 161 = 1,320.25 kcal. A man of the same height, weight and age would have a BMR exactly 166 kcal higher, and every ten years of age lowers the estimate by 50 kcal.
Limits
- An estimate for groups, applied to one person. Individual metabolism can differ from the prediction by more than 10%, especially at the extremes of body size.
- Not validated for everyone. The systematic review notes that older adults and some ethnic groups were underrepresented in the studies behind these equations. The calculator does not apply to children, or during pregnancy or breastfeeding.
- The activity levels were defined for a different equation. The FAO/WHO/UNU report expresses PAL relative to basal metabolism in general; applying it to the Mifflin-St Jeor estimate is standard practice but adds some uncertainty.
- Not a diet plan. Weight change depends on more than an energy estimate. For weight management with a medical condition, talk to a doctor or registered dietitian.
Frequently asked questions
What is BMR?
Basal metabolic rate is the energy your body uses at complete rest to keep breathing, circulating blood and maintaining temperature. It is usually the largest part of daily energy use.
Which BMR equation is most accurate?
A systematic review of the four most common equations found Mifflin-St Jeor the most reliable for healthy non-obese and obese adults.
Why is the result a range?
Because activity levels are defined as ranges. A range reflects the real uncertainty better than a single number.
How many calories do I need a day?
Roughly your BMR multiplied by 1.4–1.7 if you are mostly sedentary, more if you are active. The table shows the range for each level.
Is my data stored?
No. The calculation runs in your browser and nothing is saved.
Sources and further reading
- Mifflin MD, St Jeor ST et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 1990;51:241–7
- Frankenfield D et al. Comparison of predictive equations for resting metabolic rate: a systematic review. J Am Diet Assoc 2005;105:775–89
- FAO/WHO/UNU: Human energy requirements, section 5 (physical activity level)